SECURE SHOPPING

Wool and the “Itch” Factor

The uncomfortable sensation known as ‘itch’ or 'prickle' that is sometimes attributed to wool clothing and bedding is widely misunderstood. Common misconceptions are that it is due to an allergy to wool, or caused by the scales of the wool fibre. Both of these explanations are incorrect.

Academic research has shown that allergy to wool is quite rare, and a study has shown the lack of any correlation between a subject’s fabric prickle response and their response to wool allergen extracts via a standard scratch test. In other words, people who showed an allergic response to wool found the prickliness of a particular fabric sample no worse than those who did not show an allergic response.

Neither are the scales of the wool fibre likely to cause prickle as they are far too small, protruding less than one 1000th of a millimetre from the surface of the fibre. The degradation of wool fibre scales, routinely carried out on coarse grade wool as part of the process to make wool machine washable, does not remove prickle from a garment for which it is a problem. In spite of this, the misconception about scales causing prickle is often reported.

The actual cause of prickle in wool fabrics (and in fact in fabrics made from any fibre) is the presence of relatively coarse fibres, stiff enough to press into the surface the skin (like pinpricks). Finer fibres do not press into the skin because they buckle when pressed against it. The pain receptors in the skin only respond if sufficient force is applied to them, and for thick fibres this force is reached before the fibre bends over and buckles. For thinner fibres the pain receptor threshold is not reached before the fibre collapses. The stiffness and the length of the fibres are important too; a very flexible or long fibre has a greater tendency to collapse when its end presses against the skin. Prickle is therefore generally only a problem for wool fabrics because of the fact that thick fibres trigger the pain receptors.

Coarse synthetic fibre is just as potentially prickly as coarse wool. Research has found no difference in itch factor between garments made of wool, alpaca, mohair, cashmere, or man-made synthetics. The micron count of the fibre is the only determinant.

Wool fibres come in various grades of fineness and even the fleece from a single sheep will have fibres across a range of fineness. If these fibres are not sorted to a high enough standard, leaving too many thin weak fibres in at one end of the spectrum and too many thick coarse fibres at the other end, the resulting fabric may be passed off as “superfine” based on an average micron count, but the result with be a fabric that itches as well as being uneven and of poor quality.

Research has also established that once the average diameter of the fibre in a fabric or sweater exceeds 22 microns, or there is more than 5% of fibres exceeding 30 microns, the prickle factor begins to appear. In other words, the person wearing the garment begins to feel the itch.

Variability between humans also plays a role. Some people are less sensitive to prickle than others; they either have pain receptors that trigger only at higher forces or they are protected by a thicker layer of skin.

Some people even experience prickle simply because they think something will itch!  We have seen more than once instance where someone insists that one brand will itch and another doesn’t - even when both brands are made from exactly the same fabric!

Unfortunately for the consumer, when we looked at a number of merino fabrics all classed as “superfine”, we found a wide range of fibres being used.  Some of these were way beyond what we would call acceptable in a fabric classed as “superfine” - and these will cause itch.  There are  more here which will enlarge when clicked.

References

1.     Holcombe, B.V., "The thermal insulation performance of textile fabrics", CSIRO.
2.     Holcombe, B.V. "The sensational comfort of wool", CSIRO.
3.     Holcombe, B.V., Staying warm", Wild Magazine, Oct/Nov/Dec 1987.
4.     CSIRO, "Wool and Warmth" fact sheet,
5.     CSIRO, "Wool garments generate warmth in cool, damp conditions".
6.     Stuart, I.M., Schneider, A.M., and Turner, T.R., Textile Research Journal Vol.59, pp 324-329 (June 1989)
7.     CSIRO, "Wool for Active Sports: Comfort and Performance Advantages".>
8.     BMC Dermatology 2001, 1:6 doi:10.1186/1471-5945-1-6,
9.    Standard: ISO 139:2005 – Textiles – Standard atmospheres for conditioning and testing (2005).AgResearch Report CLR      10/17 11
10.     Test method: WNZ TM 260 – Thermal resistance of textiles (1995).
11.     Test method: BS 5636:1990 – Method for determination of permeability of fabrics to air.
12.    Comparative thermophysiological evaluations of wool and acrylic blankets, wool and polyester filled quilts. Technical Information Letter 13, International Wool Secretariat, January 1984.
13.     T H Benzinger, C Kitzinger and M W Pratt, The Human Thermostat. In: Physiological and behavioral temperature regulation, J D Hardy, A P Gagge and J A J Stolwijk (eds), Charles C Thomas, USA, 1970.
14.     L Benisek, Current flammability methods and specification, and the position of wool. Wool Science Review, 50, 1974, 40-54.
15.     N A G Johnson, E J Wood, P E Ingham, S J McNeil and I D McFarlane, Wool as a Technical Fibre. Journal of the Textile Institute, 2003, 94(3) 26-41.
16.     S M Causer, R C McMillan and W G Bryson, The role of wool carpets in controlling indoor air pollution. In: Proceedings of the 9th International Wool Textile Research Conference, Biella (Italy), 28th June to 5th July 1995.
17.     R K Garnsworthy, R L Gully, R P Kandiah, P Kenins, RJ Mayfield and RA Westerman, Understanding the Causes of Prickle and Itch from the Skin Contact of Fabrics. CSIRO Division of Wool Technology Report No. G64, 1988.
18.     P. Hadfield, Wool comes up to scratch. New Scientist, 25 October 1997, pg 7.
19.     G R S Naylor, C J Veitch and R J Mayfield, Fabric-Evoked Prickle. Textile Research Journal, 1992, 62(8), 487-493. AgResearch Report CLR 10/17 12
20.     R K Garnsworthy, R L Gully, P Kenins, R J Mayfield and R A Westerman. Identification of the Physical Stimulus and the Neural Basis of Fabric-Evoked Prickle. Journal of Neurophysiology, 1988, 59(4), 1083-1096.