Hair keeps you warm, but can it also cool you down?

A furry coat keeps animals warm on cold days. This is known. But can it also provide cooling when it's hot? South Korean researchers think so. But another expert is skeptical.

For most people you will find the highest concentration of hair on the head. The hair cap protects your scalp from harmful UV rays and keeps your head nice and warm in winter. But in the summer your locks look less fit. Your head is on average 0.4 to 2.5°C warmer than the rest of your body. This is because it consumes only 2% of body weight, but uses 20% of the energy provided by metabolism.

So you might think that a bald head (with adequate sunscreen) would be more comfortable on hot days than a thick head. South Korean researchers question this idea. she Mention that Hair can also keep your head cool. This is the conclusion from research into how hair responds to infrared radiation (also called thermal radiation).

Hair from beauty salon

Scientists studied the extent to which hair absorbs, reflects, and transmits different types of light and heat rays. For this they used black hair they collected from a local beauty salon.

Hair roughly consists of three parts: the relatively thin outer layer, which consists of a kind of scales, then comes the cortex – which is the thickest layer – and in the middle is a thin core (the medulla). The bark is composed of long fibers composed mainly of keratin protein and air sacs, which makes it flexible and able to absorb water well. Black hair also contains a lot of pigment MelaninWhich strongly absorbs light and radiation.

The researchers tested how much infrared radiation was absorbed by black hair when wet or dry. They then bleached the hair, which greatly reduced the amount of melanin. They also tested bleached locks wet and dry.

Cool hairstyle

Dry black hair appeared to be the best at absorbing and emitting the thermal infrared rays emanating from the sun. The researchers then looked at the type of thermal radiation that could be emitted by our skin, which has a different and longer wavelength than the more common infrared rays from the sun. This radiation appears to be absorbed and emitted equally by all hair types – black and bleached, wet and dry. For example, they determined how black hair responds to different types of thermal radiation.

The researchers then placed two strips of artificial skin outside at a time, during cold days and during warm days. One patch of skin was covered in hair, the other was not. During a cold day, covered synthetic leather seems to stay warmer than bare synthetic leather. No one was surprised. But on the hot day it turned out to help her too. The hairy artificial skin remained cooler than the exposed skin.

According to the researchers, this suggests that our hair was also designed to cool down. They say this research could lead to the development of biologically inspired materials that could keep us cool in a warming world.

sunhat

But not all experts agree that your hair can have a cooling effect. “The researchers examined in detail the transmission of thermal radiation from a surface covered with black textile fibers,” the researchers say. Adrian Bejan from Duke University in the United States, and has several publications on heat transfer to his name. “This may be relevant to some developments in textiles, but it has nothing to do with natural hair and does not show that hair can have a cooling effect.”

Benjan points out, for example, that South Korean researchers placed hair on artificial skin in such a way as to form a parallel layer. This is similar to the way a shirt covers the skin. This is not how natural hair grows. It is not parallel to the skin, but it protrudes.

Bijan also did not encounter a hair-cooling effect in his own research. He says: “The function of hair is to keep its owner (human or animal) warm, not to cool him.” “Fabric fibres, for example in the form of sun hats, can help with cooling, but this works differently to natural hair.”