Our hair is part of what we call the integumentary system of the human body, which also includes the skin and nails. Hair is, in fact, a type of modified skin. It is made up of keratin, a form of protein, and is produced in tunnel-like structures in the skin called follicles. Inside the hair follicle is the hair bulb that is comprised of cells that deposit keratin and melanin, which is responsible for giving your hair its color. The hair that breaks through your skin from the follicle is the hair shaft. The shaft is basically composed of dead cells comprised of keratin fibres. In fact, the totality of hair on our head is a huge lump of dead cells, which explains why we don't experience any pain when we go for a haircut.
Dupilumab is FDA approved for treating eczema aka atopic dermatitis and sold under the brand name Dupixent. As the story goes, a patient with alopecia totalis (a form of areata which leaves a person’s head completely bald) was being treated for eczema by the drug Dupixent. After 6 weeks the patient first began to notice progress in terms of hair growth and at 7 months she had noticeable pigmented hair growth on her scalp. Notably, the patient stopped taking the dupilumab for a period of time and noticed her growth subsided; when she began taking the drug again the hair improved once more. This provides another useful therapy option for patients seeking treatment for AA. One would imagine a topical version would be worthwhile to investigate.