ABSTRACT
This paper reviews published and unpublished literature on the role of wool in human health and well-being. Human-based investigations, or those involving human simulations
(manikins) were the focus. The principal parameters in the review were skin health, physical contact between textiles/garments and human skin (tactile acceptability - prickle, friction, allergies), thermal and moisture properties, human body odour, and sleep (bed
clothes/sleepwear, bedding).
INTRODUCTION
The objective of the review was to identify and critically review published and unpublished
literature on the role of wool in human health and well-being, where possible, accounting for inconsistencies in evidence in that literature. Several exclusions were applied i.e. wool in very specialised applications such as high-level human performance, and medical interventions; burning behaviour/flammability; wool in the built environment; and wool in animal health.
Findings from investigations on most of these topics have been well published.
METHOD
Evidence of the role of wool in human health and well-being was obtained by reviewing
published peer-reviewed literature, unpublished reports, and personal communications. More than 240 documents were examined. The focus was evidence based on human studies (or those from human manikins), rather than laboratory reports of fabric properties, although the latter were sometimes also considered. The principal parameters identified for the review were 1 skin health, 2 physical contact between textiles/garments and human skin (tactile acceptability - prickle, friction, allergies), 3 thermal and moisture properties, 4 human body odour, and 5 sleep - bed clothes, sleepwear, bedding. Some methodological and data issues also warranted comment with regard to interpretation of findings.
RESULTS AND DISCUSSION
1 Skin health
Skin is the human body barrier to the external environment, attributable to its physical
structure and properties. Indicators of skin health include pH, water content of the stratum
corneum, transepidermal water loss, skin elasticity.
Skin pH is typically acid, ranging from 4.0-7.0 pH: skin with <5.0pH is considered more
desirable than that with >5.0 pH (Lambers, Piessens et al. 2006); superficial layers of skin are typically 4.0-4.5 pH) (Schmid-Wendtner and Korting 2006; Darlenski, Sassning et al. 2009)).
Water content of the stratum corneum (SC) SC hydration reflects the skin response to
changing environmental conditions, and when not functioning correctly, the stratum corneum is typically 'dry' (Rawlings and Harding 2004). Transepidermal water loss (TEWL) also reflects the skin response to changing conditions and is another effective indicator of skin barrier function (Elkeeb, Hui et al. 2010), with small changes detectable (Fluhr, Feingold et al. 2006). Water content of the skin is related to elasticity and linked to age (Potts, Buras et al. 1984).
Because the skin may be in direct contact with wool/wool products, evidence of skin health and changes in this after such contact is of interest. There is a dearth of publications on skin health and its relationship with fabrics manufactured from either wool, or indeed, other named fibres. Effects of dry and wet fabric samples (n=16 different fibres and structures, including wool) on the forearm of females (n=35) for 75 minutes showed little effect on SC hydration when dry, but an increase when wet with both wool and cotton fabrics (Cameron, Brown et al.
1997). Effects of fibre content of socks on the skin health of the human foot was investigated during 2013-2014 (Laing, Wilson et al. 2014). Dress socks in four different fibre/yarn types (100% acrylic, 100% wool 24.5µm, 100% wool 20.5µm, 100% cotton) were worn in a longitudinal controlled parallel trial for a minimum of 8 hours per day over an 8-week period. Boots were standardised. Each participant (n=16 males) was taken as his own control with % change in indicators analysed. Differences were observed in the effect of sock types wool and cotton at the heel (the heel drier and in closer contact with the fabric compared to the dorsal and plantar surfaces). Although effects of the socks on the skin in terms of SC were non significant, the order of mean values was wool 20.5µm, wool 24.5µm, both positive; cotton,acrylic, both negative. Improved barrier function, indicated by a decrease in TEWL and an elevated SC, was evident at the heel.
No other completed investigation of skin health related to fibre content of skin coverings
made from wool has been identified. Preliminary findings of a study on effects of wool
fabrics against the skin of those predisposed to atopic dermatitis do seem promising (Swan,2014, personal communication).
2 Physical contact between textiles/garments and human skin (tactile acceptability -
prickle, friction, allergies)
An aversion to next-to-skin wool garments has been attributed to discomfort or a sensation of prickle, and beliefs and experiences with wool in childhood can influence future use(Sneddon, Lee et al. 2012; Sneddon, Lee et al. 2012). Prickle is understood to be mechanical irritation to the skin by coarse fibre ends indenting the skin and activating nerve endings (Garnsworthy, Gully et al. 1988; Naylor 1992; Naylor, Phillips et al. 1997). Fibre, top, yarn,and fabric factors can influence the tendency of a fabric to exhibit prickle (Naylor 1997; Naylor, Phillips et al. 1997) e.g. length of fibre protruding from the fabric surface, presence of coarse fibre ends (Naebe, McGregor et al. 2014). Methods for overcoming prickle effects include enzyme treatments (of fibers, yarns, fabrics e.g.(Bishop, Shen et al. 1998; Das and Ramaswamy 2006), and modifying yarn structure (modified wrap yarn giving a reduction of 1µm, 3µm, and 3µm for a 25µm, a 29µm, and a 31µm diameter wool fibre respectively (Miao, Collie et al. 2005).
Perceptions of wearers have been linked to prickle (McGregor, Naebe et al. 2013; Stanton,Speijers et al. 2014). Skin temperature and relative humidity can influence the perception of prickle as when sweating begins, wool garments may become less comfortable (Wang, Zhang et al. 2003). A UK-based wear trial on next-to-skin/thermal underwear in which 21µm diameter wool was used, reported approximately 30% of the male participants indicated garments were ‘scratchy’ and that same percentage of the participants also indicated the garments were thermally unacceptable (Harnett 1984). In a subsequent wear trial using 19µm diameter wool, no participant perceived the garments as itchy or scratchy (Harnett 1984).Fabric ‘pleasantness’ has been reported to decrease as temperature and relative humidity increase (Gwosdow, Stevens et al. 1986), so it is likely participants who perceived the garments too warm were those who perceived the garments as scratchy. Two Australian studies are pertinent. In one, wool fabrics manufactured from 19µm fibres were reported to have no greater prickle value than cotton fabrics when assessed in a controlled, non-standard atmosphere (22±1°C, 65±5%RH) (n=60 volunteers) (Naylor, Veitch et al. 1992). In a second, fabrics manufactured in a next-to-skin long-sleeved, fitted garment composed of fine wool (16.5µm) were ranked as most preferred by adult females (n=39 Australian, n=47 USA) over comparable garments manufactured from 18.5µm and 20.5µm wool. Garments were handled as if purchasing, so both tactile and visual cues were present (Sneddon, Lee et al. 2012). What
is not always clear in these studies is whether all other manufacturing parameters (yarn, fabric structure, fabric mass per unit area) were identical (i.e. varying fibre diameter alone), and whether test conditions were identical. When worn/directly against the skin, humidity is known to affect the sensation of prickle (Gwosdow, Stevens et al. 1986), and the perception of skin wetness in turn is influenced by interactions between thermal and mechanical stimuli (Filingeri, Redortier et al. 2014), with warm temperatures suppressing the perception of skin wetness and coldness seeming to dominate (Filingeri, Redortier et al. 2014).
Claims about rough surfaces of wool and the consequential irritation continue (Fujimura, Takagi et al. 2011). Prickle or itch is sometimes misconstrued as a ‘wool allergy’. For example, 35-40% of interviewees who would not consider buying wool garments nominated prickle as the reason, and 7-10% nominated allergy (Starick 2013).
How the human skin responds to movement of fabric across its surface (friction between
fabrics and skin) is of interest in applications such as next-to-skin garments (e.g. underwear,socks). A first response may be redness of the skin, an indicator of irritation. Several studies on fabric type and skin temperature and/or blood flow have been undertaken (Hatch, Markee et al. 1990; Gan, Cheng et al. 2010), although most do not include wool fabrics. The study by Gan, et al. (Gan, Cheng et al. 2010) measured fabrics for just five minutes on the forearm of one participant. Hatch, et al. (Hatch, Markee et al. 1990) observed skin redness in some participants, suggesting increased blood flow to that area was caused by contact between fabric and skin. Blood flow at the site was not measured, although an increase does seem probable.
Formation of friction blisters is relevant to the sock and glove manufacturing sectors. These blisters form in two main stages: surface forces produce a shearing effect between the stratum corneum and granulosum which causes an intra-epidermal cleft; then fluid flows into this cleft to form the blister (Sulzberger, Cortese et al. 1966), typically within one or two hours (Akers and Sulzberger 1972). Issues in blister formation include the magnitude of the frictional force and the number of cycles a material passes over the skin (Knapik, Reynolds et al. 1995), and the presence of moisture on the skin (Sulzberger, Cortese et al. 1966; Highley, Coomey et al. 1977; Nacht, Close et al. 1981; Knapik, Reynolds et al. 1995). The lower coefficient of friction of very wet skin may be due to a sufficient volume of water present to act as a lubricant between the skin and another material (Knapik, Reynolds et al. 1995).
Thus, in relation to foot coverings, the three important parameters are how textiles respond in the presence of moisture; friction between the skin surface and the sock fabric; compression and compressional resistance/recovery of the sock fabric. Reports of the superiority in sock performance of one fibre type over another, particularly through the 1980s and 1990s,included comparisons of acrylic with cotton or wool socks (Morris, Prato et al. 1984; Euler 1985; Brooks, Capablanca et al. 1990; Herring and Richie 1990; Herring and Richie 1993).More recently, sock fabrics manufactured from mid-micron and fine wool were reported to have a lower coefficient of static friction than fabrics composed of acrylic in both dry and damp conditions when measured against a synthetic skin (van Amber, Lowe et al. 2014).Given that fibre type, yarn structure, and fabric structure are all manufacturing variables and thus controllable, their relative effects on frictional properties are of interest. Fabrics in this study were prepared for a factorial experiment (100% wool mid-micron (26µm), 100% wool fine (19µm), 100% acrylic (19µm); yarn high twist, low twist, single; single jersey, full terry, half terry). The lowest coefficient of static and dynamic friction was evident with the single jersey: with respect to damp fabrics, that made from fine wool exhibited the lowest coefficient of static friction and acrylic the highest.
Compression/compressional resiliency of socks, including wool socks has been reported.
Wool cushioned socks have been shown to have a greater shock-attenuating effect than
walking barefoot (Howarth and Rome 1996), and wool socks were also associated with an
increased time to peak force, and decreased propulsive force than when the participant(s) was walking bare footed (Blackmore, Ball et al. 2011), unsurprising in both cases. Differences detected were attributed to differences in thickness of the socks (i.e. fabric structure and sock construction had a more important shock-attenuating effect than the type of fibre (Blackmore,Ball et al. 2011). Similarly, fibre type was not a significant factor in the percentage of thickness retained under compression (van Amber, Lowe et al. 2014), but was relevant in compression:recovery ratios, the acrylic fabrics being superior to the two wool fabrics when fabrics were damp. The authors did caution against potential misinterpretation, as the fabrics held different amounts of moisture (van Amber, Lowe et al. 2014).
Claims of allergic reactions to wool arise from three potential sources: chemical (e.g. lanolin,residues of chemical substances used in processing), physical (irritation from prickle, largely now resolved), and allergens (e.g. insects/mites typically associated with carpets/furnishings).
One possible chemical explanation for wool allergy is in relation to lanolin on wool, not the
fibre itself. A review of 24,449 patients in Britain from 1982-1996 reported a 1.7% annual
rate of sensitivity to lanolin or wool alcohol, highlighting the relatively low sensitivity in this
British sample (Wakelin, Smith et al. 2001). During the 1980s Hatch and others sought to
identify dermatological problems related to fibre content and dyes (Hatch 1984), with little
published since that time. Whether a causal link exists between chemical substances in textile products (allergens) and allergic reactions was investigated in a cooperative study in Italy involving The Textile and Fashion Federation, The National Federation of the Chemical Industry, and the Italian Association of Allergological, Professional and Environmental Dermatology (Associazione Tessile e Salute-Health and Textile Association 2013). This report identified contact dermatitis mostly caused by fabric dyes, but also finishing resins and adhesive resins, particularly when these release formaldehyde. Prevalence and sensitisation to formaldehyde was reportedly decreasing. 'Emerging allergens' were noted, attributable to non-European manufacturers particularly those from Asia (Associazione Tessile e Salute-Health and Textile Association 2013).
An epidemiological study (n=401 patients, aged 5-84 years) showed fabrics were the cause of contact dermatitis in approximately 70% of cases, metallic and garment accessories in approximately 17% of cases, and shoes in approximately 14% of cases (Associazione Tessilee Salute-Health and Textile Association 2013). Dyes and intermediary agents accounted for 44% of cases: garments most commonly involved were nylon stockings (8.9%), underwear (13.4%), shirts (13.0%), trousers and skirts (13.8%), and sportswear (8.1%) (Associazione Tessile e Salute-Health and Textile Association 2013). Other than nylon (stockings) no mention was made of fibre content. That sweat on the skin under fabric is likely to affect permeability of those fabrics to chemical transfer has been long recognised (Raheel 1991), although no wool-related evidence has been identified.
With respect to chemical risk in pure new wool textiles, manufacturing companies are
required to ensure the safety of their products through declaring compliance with Restricted Substance Lists. These restrictions appear specific to members of the EU.
The physical properties of wool fibres (e.g. stiffness, micron) have been identified as causing an unpleasant sensation and the desire to scratch, and a possible trigger of atopic dermatitis (Ständer and Steinhoff 2002). In the 1980s, wool fibres were reported as causing acute and cumulative irritant dermatitis as well as aggravating atopic dermatitis (Hatch and Maibach 1985). However, by the 1990s, wool as a skin irritant caused by prickle, was better understood (Hatch and Maibach 1995), and although some residual misunderstanding remains (Fujimura, Takagi et al. 2011), atopic dermatitis is not wool allergy.
3 Thermal and moisture properties
Many advantages of including wool fibres in textiles for human health and well-being derive from the chemical composition and structure of the fibre, particularly those related to thermal and moisture properties. Molecules in the fibre are able to create hydrogen bonds with water, immobilising the water and incorporating it into the fibre, with a small amount of heat released (Leeder 1984; Leeder 1984). This is detectable in fabric form (Laing, Niven et al. 2007), in garments in use (Laing, Sims et al. 2008), and in bedding (Naylor, 2014, personal communication). Physical structure of the wool fibre (e.g. crimp, scaled surface) is a major determinant of yarn properties irrespective of whether processed by the woolen or worsted system, and largely irrespective of yarn twist. That wool (i.e. wool products) is considered by end-users to be 'warm' is due primarily to fibre bulk and crimp, which lead to bulkier yarns and yield thicker, more thermally resistant fabrics/end products (Harnett 1984; Leeder 1984), and many papers published during the 20th century show this.
Thermal properties of a fabric are derived from one or more of four parameters: thickness,
thermal conductivity, absorptivity, and heat of absorption. Wool fabrics are regarded as
providing superior thermal properties under both damp and wet conditions. The small amount of heat released with absorption of water, and wool fibres/fabrics reported as having a lower thermal conductivity than cotton, polypropylene or acrylic, underscore these advantages (Schneider, Hoschke et al. 1992). Fabrics composed of wool have been reported as absorbing more moisture than matched fabrics composed of synthetic fibres such as nylon, polyester,and acrylic (Collie 2002; Laing, Niven et al. 2007; van Amber 2013). Absorption of liquid from the skin results in perception of drier and therefore warmer skin (Laing 2009). Recent evidence confirms perception of warmth is affected by perception of wetness (Filingeri, Redortier et al. 2014) with warm temperatures suppressing the perception of wetness(Filingeri, Redortier et al. 2014). Further, surface wetness of fabrics in contact with the skin influences more general perceptions of comfort (Scheurell, Spivak et al. 1985).
Garments composed of wool when worn have been reported to have lowered the relative
humidity at the skin surface compared to garments composed of acrylic fibres (Li 2005).
Wearing wool garments has also been reported to delay the on-set of sweating and result in smaller changes in core temperature than when wearing matched polyester and wool/polyester plated garments (Laing, Sims et al. 2008). Buffering is the probable explanation for these long-sleeved wool upper body garments resulting in smaller changes in core temperature and smaller increases in heat content in both cold and hot conditions than identical polyester garments (Laing, Sims et al. 2008). Participants wearing the wool garment also had a lower heart rate during all test conditions (Laing, Sims et al. 2008). Buffering effects of wool fabrics/garments compared to polyester (long-sleeved tops) have also been reported by Li et al Holcombe and Apcar (Li, Holcombe et al. 1992), and wool blankets compared to an acrylic/cotton blend reported by Umbach (Umbach 1986).
Smooth, lightweight wool fabrics have been shown to be perceived as cooler to the touch
(forearm test, n=20 participants) than comparable woven fabrics of cotton, polyester and a
wool/polyester blend, with an immediate drop of 0.4-0.8°C observed in skin temperature on the forearm (Schneider, Holcombe et al. 1996). These and other similar findings on
lightweight fabrics of the latter part of the 20th century led to new commercial markets for
apparel.
The thermal resistance of wool fabrics has also been attributed to improvement in specific
aspects of user health. Use of wool undergarments (and bedding) over a six-week period was reported to reduce symptoms and drug use of patients suffering from fibromyalgia (Kiyak 2009). Details on construction, mass per unit area, thickness, and laundering practices were not reported for either the undergarments or the bedding.
4 Human body odour - textiles, clothing, footwear
Basic understanding of body odour and several links to clothing have been known since the 1950s (Shelley, Hurley et al. 1953): human apocrine sweat, a sterile fluid, is acted on by bacteria and other organisms residing on the skin (e.g. Staphylococcus, Micrococcus,
Bacillus, Acinetobacter, Klebsiella, Enterobacter and Streptomyces (Kloos and Musselwhite 1975)), releasing volatile acids and indoles (e.g. isovaleric, butyric, carbonic). Major sources of body sweat odour are those emitted by the apocrine glands (i.e. fatty acids, steroids,amines). Axillary hair collects sweat and other debris, and in relation to foot odour, similar patterns occur with some different organisms (Marshall, Leeming et al. 1987; Marshall, Holland et al. 1988; Ara, Hama et al. 2006). Strong foot odour has been linked with greater total population densities of microflora, staphylococci and aerobic coryneforms, rather than an increase in any single type of bacterium (Marshall, Holland et al. 1988).
In the 1970s, isovaleric acid (the ‘sweat-like’ odour) was identified as one of six main
primary odours (Amoore 1977), and one to which 3% of the general population is anosmic. A study of ten males (25-30 years old) (n=5 strong foot odour, n=5 low or no odour) showed isovaleric acid identifiable in all participants with foot odour, but not in those without (Kanda, Yagi et al. 1990). All odour assessors in this study could detect isovaleric acid at a concentration of 100ppm (Kanda, Yagi et al. 1990). While isovaleric acid is responsible for foot odour (Kanda, Yagi et al. 1990), propionic acid, isobutyric acid and butyric acid are also contributors (Ara, Hama et al. 2006).
Clothing adjacent to the axilla or textiles covering the foot (socks, shoes) are implicated in
human body odour, as organisms are able to reside in various fabrics (Shelley, Hurley et al. 1953) and in footwear. Minimising this odour is another measure of ensuring well-being. Understanding the interactions among axillary odours, bacterial count and fibre type improved during the early part of the 21st century (McQueen, Laing et al. 2007; McQueen, Laing et al. 2007; McQueen, Laing et al. 2008). Using a sensory panel (n=13) McQueen et al, assessed the odour of fabric samples (wool, polyester, cotton; interlock, single jersey, 1x1 rib,matched constructions) which had been worn by five males. Polyester fabrics exhibited the strongest and wool fabrics the least intense odour. No inherent antibacterial properties were evident, with bacterial counts at day 1 similar on all fabrics. Bacterial populations were present on all fabrics for up to 28 days, with numbers remaining relatively stable in wool fabrics, and declining in polyester fabrics (McQueen, Laing et al. 2007). Whether the bacterial count was related to the method of extraction is unknown but is considered unlikely to explain the observed differences in odour intensity.
Intermittent claims are made about wool being naturally antibacterial, but no evidence to
support these claims has been identified. As noted results from the study by McQueen, et al. (2007) did not show a link between the number of bacteria and odour. Nor has any evidence of anti-fungal properties related to wool been identified: investigations of skin-based fungi and odour seem not to have been undertaken. The notion of natural antibacterial/ antimicrobial properties may arise from the fact that wool products such as garments do not retain/ release odour volatiles during and following wear as do comparable products in other fibre types. Exposure of a matrix of known odour volatiles to wool, cotton, polyester fibres/yarns under controlled conditions is in progress and will provide further explanation of the mechanisms involved (Yao, Laing et al. 2014).
Treatments to confer antimicrobial properties on textiles have been developed and many
reviewed (Gao and Cranston 2008). One method applied to selected wool and wool products has been inclusion of silver (Li, Xie et al. 2010; Tang, Wang et al. 2011) although concerns have been expressed about development of bacterial resistance to silver (Percival, Bowler et al. 2005). Effectiveness of other wool-metal complexes/salts has also been examined (Freddi, Arai et al. 2001; Zhu and Sun 2004; Zhao and Sun 2006), as has chitosan as an antimicrobial treatment for woolen fabrics (Hseih, Huang et al. 2004).
The effect of footwear on temperature and humidity, and therefore microbial populations on skin of feet was investigated in the 1960s, but with little information on footwear, including socks. A study of the socks and shoes of hospital patients with symptoms of tinea pedis but not undergoing treatment (n=30) focussed on these items of clothing as carriers of fungal spores (Brown and McLarnon 2007). Although non-significant, there was a trend for participants with tinea pedis infections to also have infected footwear (Brown and McLarnon 2007). That fungal spores remain in socks, shoes, and on various surfaces has been assumed given high levels of transmittance and re-infection (Ajello and Getz 1954). The relationship between the adhesion of dermatophytes and footwear has also been explored. In none of these studies have wool socks/shoes been included.
5 Sleep - bed clothes, sleepwear, bedding
Clothing worn during sleep (e.g. pyjamas, nightdresses, 'stretch-and-grows'/ 'onesies') has the potential to influence sleep quality, and several variables indicate sleep quality (e.g. time to the on-set of sleep, duration of sleep, duration of wakefulness).
There is some evidence that the quality of sleep can be affected by the type of fabrics in both bedding and clothing worn in bed. Most investigations have not included wool (e.g. pyjamas of cotton/elastane compared with those of polyester/elastane (Yao, Tokura et al. 2007).Patterns of sleep among pre-school children (n=101, aged 2-5 years) was the focus of an Australian study on effects of bedding, bedroom environment, sleep hygiene, and sleep patterns. Sleepwear was typically cotton in winter and summer, with cotton/ synthetic sleepwear reportedly worn by about half the children. Few children wore sleep clothing made from wool fabrics, just 7% of children in winter (Richdale 2013).
Effects of sleeping apparel (wool, cotton) and bedding (wool, synthetic) on sleep of 17
participants (adults, aged 24.6±6.9 years; n=10 males, n=7 females) over nine nights of sleep have been examined (Shin, Swan et al. 2014 ). Participants were randomly allocated to one of two ambient conditions (17°C, 22°C), to the sleeping apparel, and to the bedding types. Wool bed apparel was shown to promote sleep through a shorter time to the on-set of sleep, and the total sleep time was suggested as being longer, although not significantly so. Effects of bedding were less clear. Differences were attributed to the general hygroscopicity, high moisture absorption rate, and thermal resistance of the wool textiles. Full detail on fabric structures and properties and on garment design is available in a paper shortly to be published by Shin et al. Detail of human physiological thermal indicators will be provided to assist understanding.
Sleep in adult humans becomes disrupted once thermoregulatory mechanisms are elicited
(Bach, Telliez et al. 2002), and information on many aspects of temperature and sleep has
been published (REM, (Muzet, Ehrhart et al. 1983; Okamoto-Mizuno, Mizuno et al. 1999);
room temperature, bed temperature, and various body temperature indicators (Muzet, Ehrhart et al. 1983; Okamoto-Mizuno, Mizuno et al. 1999); effects of elevated skin wettedness (Okamoto-Mizuno, Mizuno et al. 1999). Temperature of the sleep environment is even more important for infants, as temperature has been suggested one cause of Sudden Infant Death Syndrome (SIDS) (Muzet, Ehrhart et al. 1983; Stanton 1984). A pilot study in the UK in the early 1980s reported low birthweight babies gained more weight when nursed on lambswool (either lambswool in an artificial fibre backing or natural lambskins) rather than cotton sheets (Scott, Cole et al. 1983). The authors hypothesised that the wool provided a more thermally neutral, ‘less stressful’ environment. although these findings were later challenged on the grounds that reported significance was based on absolute weight gain rather than a percentage of initial body weight (Roberts, Savage et al. 1986). The study was repeated with monitored energy intake, and no significance detected (Roberts, Savage et al. 1986). During the latter part of the 20th century and early 21st century Wilson and colleagues examined infant sleep arrangements and the links with SIDS (Wilson, Taylor et al. 1994), particularly thermal parameters (Wilson, Laing et al. 2000; Wilson, Laing et al. 2002). Use of a wool underblanket with a ‘waterproof’ covering has previously been reported as contributing to a lower likelihood of the incidence of SIDS (Wilson, Taylor et al. 1994). These investigations demonstrate the complexity of bedding and its effects.
Since the classic 1980s investigation by Umbach (Umbach 1986), understanding the role of bedding is slowly being enhanced. Umbach compared performance of a wool blanket with another from acrylic, matched as well as possible for thickness, mass per unit area, a
comparison based on skin model, instrumented human manikin (Charlie) dressed in pyjamas, and also with humans (n=4 males in a climate chamber). The wool blanket performed better with respect to thermal insulation, moisture absorption, and moisture buffering. With respect to underlays, investigations during the latter part of the 20th century focussed largely on sheepskins or pile-type constructions. Participants (n=10) sleeping on a wool ‘fleecy’ underblanket were observed to have 20% more periods of immobile sleep and more participants self reported feeling better in the morning and having improved sleep quality (p≤0.05) (Dickson 1984). Better understanding of potential effects of fibre/ fabric/ structure would be possible had full details been provided on both mattress pads (e.g. fibre content, construction, mass, thickness).
Bed covers used on Australian pre-school children (n=101) (Richdale 2013) in winter were
either duvets (doonas) or blankets (approximately equal numbers of each), and wool featured as fill in 26% of duvets (doonas) and 28% of blankets. In summer, the most common cover was a cotton blanket (44%) and wool just 12%. Sheets were common in summer and winter.In terms of underlays, these were cotton for approximately one third of the sample irrespective of season: wool underlays were much less common, with 12% in winter and 10% in summer (Richdale 2013). A sleep problem was associated with synthetic bed wear in winter and in summer, and feeling 'too cold' during sleep (Richdale 2013). This study involved multiple factors: differences in fabrics/ structures, fibre types self reported, and some categories of variables not mutually exclusive (e.g. the underlay mattress protector (waterproof) may have been used with either a cotton or a wool underlay). However, children who slept in any synthetic bed wear in summer or winter were significantly (weak) more likely to be reported as having a sleep problem.
CONCLUSIONS
This review provides evidence of the contribution of wool to human health and well-being.
What is known includes
1. Indicators of skin health are measurable, and textiles in close contact with the skin can
affect these. For example, wool fabrics in close contact with the skin can maintain and/or
enhance normal moisture levels of the skin.
2. The mechanisms underlying prickle resulting from skin contact with wool fabrics are well
understood, and can be ameliorated by manufacturing processes at fibre, yarn, and fabric
stages. For some consumers however, perception of it remains a barrier to use.
3. Effects of fabric structure dominate many performance properties when all variables other than fibre type are controlled. This relates particularly to thermal and moisture relationships.
4. There is no evidence to support claims that wool fibre causes allergic reactions. Allergic
reactions may occur as sweat from the human body reacts to finishes on wool fabrics, or
fabrics of any other fibre type, which are in contact with the skin surface.
5. Wool in garment form provides benefits during exercise by slowing thermophysiological
responses, thereby allowing adaptation to the changed environment.
6. There is physical and perceptual evidence of smooth, lightweight, woven wool fabrics being cooler to the touch than comparable fabrics in several other fibres/blends.
7. Thermal and moisture transmission through a layered garment assembly is not the sum of properties of the individual layers and air spaces. Effective cooling of the human body through evaporative heat loss is decrementally affected by layers, up to 80% reduction in
effectiveness.
8. There is no evidence to show wool is intrinsically antibacterial or antimicrobial. Wool
yarns/fabrics are treated to confer antimicrobial properties, and while of some benefit,
consumer concerns have been raised.
9. Wool fabrics (garments) after wear, have less intense odour than matched cotton or
polyester fabrics (garments): intensity of odour seems not to correspond with the number of bacteria extracted, and adsorption/ release of odour volatiles from wool differs to that from other fibres.
10. There is some evidence that wool blankets perform better than equivalent acrylic/blend blankets from a human thermophysiological perspective. Other than for babies and infants, little is known about effects of underlays on sleep.
Understanding the role of wool in human health and well-being is not straight forward as both investigative approaches and level of detail provided in reports/papers differ widely. Although standard test methods may be followed (e.g. ISO, ASTM, BS), different standard methods purportedly measuring the same parameter may not do so. Description of methods followed and materials used are not always complete. Fibre-based comparisons are often confounded with other manufacturing variables by insufficient control of yarns/ fabrics/ finishes. Caution in interpretation is therefore required. A challenge for the wool sector continues to be identification and demonstration of clear advantages to human health and well-being
attributable to wool, notwithstanding the good progress being made. This requires clarity in planning and executing all stages in the research - full explanation of materials, methods, corroboration with other findings, possible explanations for differences, publication in peerreviewed journals. Alignment of test procedures with those accepted internationally is one way to facilitate acceptance of the merits of wool by international consumers.
ACKNOWLEDGMENTS
This paper is based on a review prepared for and funded by the International Wool Textile
Organisation, Belgium, and Australian Wool Innovation, Sydney, Australia. Contributions to
sections of that review are acknowledged and included: Mr David Crowe, AWTA,
Melbourne, Australia; Mr Mauro Rossetti, General manager, Associazione Tessile e Salute, Biella, Italy; Mr Pier Giorgio Minazio, European technical service manager, Woolmark Italy,
Biella, Italy.
