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The Missing Link

The Missing Link #12: Hair

by Lin Abigail Tan

~A weekly column exploring the delightful, most arbitrary intricacies of our world through the lens of medicine~

Besides intermittent existential crises and Great-great-great-etc. Uncle Neanderthal, what do all humans have in common? 


We are mammals, after all. These days, we probably don’t think much about our hair beyond the morning groomings or occasional windy day, but it’s still an important part of us and has served quite well in the variegated patchwork of evolutionary history. Hair serves as a means for temperature regulation–both insulation and cooling (sweat evaporating from damp hair). It also protects against the sun’s deleterious UV rays. In animals, hair/fur coloration can even help with sexual attraction, as with the mane of a male lion (though, can the same be said about humans??) 

Hair comprises keratin, a type of fibrous structural protein. The average person has somewhere between 100,000 and 150,000 strands of hair, shedding 50-150 strands a day. Other than bone marrow, hair is the fastest growing tissue in the human body. And even though the strands of hair above the skin’s surface are technically not alive, there are a variety of conditions that can affect them.

Here are some common conditions/diseases that affect our luscious locks. 

  • Hirsutism: A condition in which women have excessive hair growth, especially on the face, chest, and back. Caused by overabundant androgens.
  • Alopecia areata: An autoimmune skin disease that causes hair loss on the scalp, face, and other areas of the body. It is a polygenic disease, meaning that both parents must contribute certain, specific genes in order for the child to display the condition (however, newer research shows there might be environmental factors at play as well). 
  • Head lice (sorry): The tiny insect that is the horror of parents and teachers everywhere is an ectoparasite–a parasite that lives outside its host. The head louse is grayish-tan and feeds on human blood from the scalp. The female excretes an adhesive substance that allows eggs to stick to the hair shaft. 
  • Dandruff: Considered a mild form of seborrheic dermatitis (a disorder that causes itchy, scaly skin), dandruff is a common condition that causes flaking skin on the scalp. It can be caused by dryness, oversensitivity, oils, or fungus. 

“Coconuts both produce milk and have hair. Ergo, a coconut is a mammal.” 

~another post I saw on Instagram

Works Cited

Alopecia Areata.” Alopecia Areata | National Alopecia Areata Foundation.

Dandruff.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 11 Sept. 2019.

Head Lice.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 1 Dec. 2018.

Hirsutism.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 14 Dec. 2019.

Ten Interesting Facts About Hair: The Original Mane ‘n Tail: Personal Care.” The Original Mane ‘n Tail | Personal Care, 5 Apr. 2019.

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