Why is wool itchy?

A knitted wool sweater may be one of the warmest pieces of clothing to grab when temperatures turn chilly, but this insulating material can often be downright itchy when wearing it.

So, what is it about wool that triggers us to itch uncontrollably?

One of the main reasons an otherwise cozy piece of clothing can go from being comfortable to unbearable is the thickness of the wool fibers used to make the item.

"The thicker the fiber, the itchier the wool will be," Ingun Grimstad Klepp, an ethnologist and professor of clothing and sustainability at Oslo Metropolitan University in Norway, told Live Science. "That's one factor. Another is the softness of the fibers used to make the yarn."

In other words, a thicker fiber spun by humans will likely be more abrasive and less flexible, which can lead to itching and irritation on the skin, while thinner, softer fibers, such as merino wool and downy-like alpaca fleece, can help "ditch the itch."

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While it's easy to assume that all wool is derived from one source — sheep — the word "wool" actually applies to shorn animal fibers that are woven into yarn to make clothing. So goats, alpacas, camels and rabbits can also provide wool, according to Science Norway, an online science news magazine. The underhair that makes up wool, which is soft, thin, curly and flexible, never stops growing, which is why these wooly animals need to be periodically shorn.

Another less common cause of itchiness is the presence of lanolin, a waxy substance secreted by the sebaceous glands of wool-bearing animals. Also called wool wax or wool grease, lanolin is great for repairing dry, chapped skin, but it can also cause an allergic response in some people, according to Healthline. 

"Wool isn't an allergen in and of itself, but it is possible to be allergic to lanolin," Grimstad Klepp said. "However, most wool today doesn't contain much lanolin because the majority of it has been washed and dyed out during production, so there's not much lanolin left in the yarn."

Despite the occasional discomfort, wool is one of the best materials to wear when it's cold and wet outside. That's because it has natural capabilities that can wick away sweat and moisture from the surface of our skin, according to Science Norway. 

"The difference between cotton and wool is that when cotton fibers get wet, they tend to get damp and collapse," Grimstadd Klepp said. "You can see this happening with people at the gym who are wearing cotton T-shirts that cling to their bodies as they sweat. Wool T-shirts have more breathability and are able to absorb quite a bit of sweat and pull it away from your body."