Some people embrace their underarm hair, others go to great lengths to get rid of it. But why do we grow it in the first place?
Beaut's science expert Dr Regina Kelly is a Science Educator and a Dean’s Postdoctoral Fellow in STEM Education at EPI*STEM, the National Centre of STEM Education, School of Education, Faculty of Education and Health Sciences, University of Limerick.
People go to great efforts to remove it, but have you ever actually thought about why we have underarm hair? What is the purpose of the hair? Scientists have put forward different theories to answer this question. The word theory in science is different from the use of the word theory in everyday language. In everyday conversations, when people use the word theory they are referring to a feeling or a guess. In science, the word theory is used to describe a justified explanation that has been formed through a range of scientific practices and has been repeatedly tested.
Samantha Prior, Associate Teacher in the Department of Biological Sciences at the University of Limerick explains some of the theories that have been put forward to explain the purpose of armpit hair. Puberty induces the growth of armpit hair. There are many proposed functions for the presence of armpit hair, these include:
To reduce friction
Armpit hair is theorised to help reduce friction under our arms. The constant rubbing of skin on skin can cause discomfort and the armpit hair acts as a barrier to reduce skin rashes and irritation.
To produce pheromones
Another theory is that armpit hair exists for the purpose of being soaked in pheromones (mate-attracting hormones).
To keep our body temperature in check
Armpit hair can regulate body temperature. It keeps our body temperature warm when we get cold by creating an insulating layer over the skin and repels sweat when we get too hot. It also soaks up the sweat and moisture that develops in the underarm area aiding in ventilation.
On the microbial level, a person's underarms has lots of different microbes which are good for our skin. These microbes are collectively known as the skin flora or skin microbiota. Recent studies show that for every human cell in the body there is at least one microbial cell and the skin is no different. Your skin is home to thousands of non-disease causing microbes that feed off your body's dead skin cells and nutrients present in your bodily excretions (yuck!). However, it seems that these microbes are not just tagging along for the ride, they provide some beneficial effects, which is why they are considered mutualistic. We feed them and provide them with a home and they prevent the growth of nasty microbes either by competing for nutrients, secreting chemicals against them, or stimulating the skin's immune system.
Fun facts about hair
- There are different types of body hair. Thick hair like armpit hair and beard hair is called terminal hair. Arm hair is finer and called vellus hair.
- You may not like to admit it but in general, hair can grow anywhere on the body except on the palms of your hands, the soles of your feet, mucous membranes, eyelids and lips. This is because there are no hair follicles on these parts of the body.
- Men typically have slightly higher numbers of hair follicles on their bodies. Men usually have more terminal hair and women have more vellus hair.
- There is also a difference between hair colours. Redheads have fewer hair follicles than brunettes and blondes. But, before you start celebrating, this refers to your NATURAL hair colour. Even though redheads have fewer follicles, on average natural red hair has a greater cross-sectional diameter so each strand is thicker.
- Why grey? As you age, the pigment cells in the hair follicles stop producing melanin. Melanin gives our hair its colour.
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