Many people consider themselves to be allergic to wool because they have an adverse reaction every time it touches their skin. However, a true allergy to wool is actually rare. Most people who have a reaction to wool do so because they have sensitive skin, and they would likely have a similar reaction to any coarse fibre. An allergy would require a person to have had a prior contact with the wool that would cause a cell-mediated hypersensitivity against it. People with sensitive skin who would like to wear wool can put a layer of softer fabric between the wool and their skin.
Wool's scaling and crimp make it easier to spin the fleece. They help the individual fibres attach to each other so that they stay together. Because of the crimp, wool fabrics have a greater bulk than other textiles and retain air, which causes the product to retain heat. Insulation also works both ways; Bedouins and Tuaregs use wool clothes to keep the heat out.
The amount of crimp corresponds to the thickness of the wool fibres. A fine wool like Merino may have up to a hundred crimps per inch, while the coarser wools like karakul may have as few as one to two crimps per inch. Hair, by contrast, has little if any scale and no crimp and little ability to bind into yarn. On sheep, the hair part of the fleece is called kemp. The relative amounts of kemp to wool vary from breed to breed, and make some fleeces more desirable for spinning, felting or carding into batts for quilts or other insulating products.Wool is harder to ignite than most synthetic and cotton fibres used in equivalent products (higher ignition temperature); it has lower rate of flame spread; low heat release and low heat of combustion; doesn't melt or drip; forms a char which is insulating and self-extinguishes; and contributes less to toxic gases and smoke than other flooring products when used in carpets. Wool carpets are specified for high safety environments such as trains and aircraft. Wool is often specified for fire-fighter garments.Wool is static resistant as the retention of moisture within the fabric prevents a build-up of static electricity.
Wool straight off a sheep contains a high level of grease which contains valuable lanolin, as well as dirt, dead skin, sweat residue, and vegetable matter. This state is known as "grease wool" or "wool in the grease". Before the wool can be used for commercial purposes it must be scoured, or cleaned. Scouring may be as simple as a bath in warm water, or a complicated removed by the chemical process of chemical carbonization. In less processed wools, vegetable matter may be removed by hand, and some of the lanolin left intact through use of gentler detergents. This semi-grease wool can be worked into yarn and knitted into particularly water-resistant mittens or sweaters, such as those of the Aran Island fishermen. Lanolin removed from wool is widely used in the cosmetics industry, such as hand creams, industrial process using detergent and alkali. In commercial wool, vegetable matter is oftenAfter shearing, the wool is separated into five main categories: fleece (which makes up the vast bulk), broken, pieces, bellies and locks. The latter four are pressed into wool packs and sold separately. The quality of fleece is determined by a technique known as wool classing, whereby a qualified wool classer groups wools of similar gradings together to maximise the return for the farmer or sheep owner. Prior to Australian auctions all Merino fleece wool is objectively measured for micron, yield (including the amount of vegetable matter), staple length, staple strength and sometimes colour and comfort factor.