Trauma to hair bulb
The living part of the hair is the bulb, which is deep to the surface of the scalp.
Hair shaft is the non-living part. Hair dye, bleach, or perms do not cause permanent damage to the root of your hair, so the follicle
can still regenerate another shaft. However, treatments that cause scarring
such as hot combing or very tight braids or any process that cause scarring, resulting in permanent loss.