From Geoff Naylor, CSIRO Division of Wool Technology
Geelong, Australia
Unfortunately, your article’s explanantion of why some wool products “itch”
is incorrect
(This Week, 25 October, p 7).
The “itch” or skin comfort of wool garments has been the subject of an
extensive research programme at CSIRO, supported by Australian woolgrowers’ funds.
If samples of wool and acrylic—which are chemically quite
different—are matched in terms of the fibre diameter and fibre mechanical
properties, then the two fabrics give the same level of skin comfort. Acrylic
fibres have a smooth cylindrical surface, unlike the characteristic wool scale
structure claimed in the article to be central to the sensation. The underlying
mechanism is related to the mechanical properties of fibres and not the fibre
type, chemical composition or detailed surface morphology.
The diameter of the individual fibres in any wool sample is quite variable,
typically 10 to 40 micrometres for apparel wools. After manufacture into a
garment, some wool fibre ends always protrude above the fabric surface and can
press against the skin during wear. These fibre ends will bend or buckle if the
applied load exceeds a critical value. This maximum force is highly dependent on
the fibre diameter.
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The thin protruding wool fibre ends simply bend or buckle under the forces
applied by the clothing, whereas the thicker fibre ends, typically those thicker
than about 30 micrometres, are able to “push” hard enough against the skin to
trigger nerve endings lying just below the skin surface. Too many triggered
nerve endings in a local area of the skin are interpreted in the brain as the
unpleasant sensation referred to as “itch”. Thus the sensation has a purely
mechanical origin and is not in any way a chemical or allergenic response.
Different wool qualities contain different mixtures of coarse and fine
fibres. Discomfort only arises when coarser wool qualities are inappropriately
used in next-to-skin garments.
This CSIRO research has led to two new retail sub-brands “merino extrafine
wool” and “pure merino wool” for the familiar Woolmark symbol. These sub-brands,
based on wool fibre diameter criteria, identify consumer garments made from
appropriate wools for next-to-skin comfort.
