Hair shedding can be caused by heat damage from blow-dryers, curling irons, flatirons, hair dyes and extensions, according to Cinya Burton for Beautylish. It can also be caused by vitamin and protein deficiencies or a thyroid imbalance. The American Academy of Dermatology lists additional causes as weight loss above 20 pounds, giving birth, experiencing high levels of stress, high fever, surgery and changes in birth control dosages.
It is normal to shed between 50 and 100 hairs a day, according to the AAD. Anything above that rate is considered excessive. Hair shedding is officially referred to in the medical field as telogen effluvium. Hair shedding may not occur until a few months after a stressful event has taken place and should only last temporarily. In cases where stress is prolonged, hair shedding continues. Otherwise, the AAD says that it should resolve itself within six to nine months as the body readjusts to normal levels.
Hair shedding is different from hair loss, which occurs when something in the body prevents the hair from growing altogether. Examples include people who undergo chemotherapy or radiation during cancer treatment. Hair loss can be hereditary. Dermatologists are able to differentiate between normal hair shedding and permanent hair loss, so the AAD recommends visiting a doctor to assess the symptoms related to thinning hair.