Hair Stopped Growing But Has Not Fallen Out

i have a friend thats hair has stopped growing all together on one side. it hasnt fallen out an the scalp. it isnt red, sore, or look infected. i was wondering what could cause this?

It is not easy to make a diagnosis without the right information. I will assume that your friend is a young man and that he may be undergoing early male patterned genetic balding. Some men who are losing their hair from genetic causes will just stop growing their hair in the impacted area. Although this is not the common presentation, it does occur and it may last for months, even years before it falls out. The hair is often miniaturized (small, thinner hair shafts) and eventually a bald area will appear. Live hair follicles never stop growing and going in and out of their growth cycle.