Parsi Teb Physical and Mental Health Journal 
What are causes of hair loss?
There are many causes of scalp hair loss, and they do differ in men and women. This article will cover the common ones. Studies show that losing up to 100-150 hairs per day is normal. Human hair naturally grows in three phases: anagen, catagen, and telogen. Anagen is the active or growing phase. Catagen is a fairly short phase of the natural hair cycle during which hairs begin to break down. Telogen is the resting phase. The hairs that are shed daily are often in the resting or late phase in the hair cycle. Normally, about 10% of the scalp hairs are in the resting or telogen phase at any time. These hairs are not growing and are getting prepared for cyclic shedding.
In general, most hair loss is not associated with systemic or internal disease, nor is poor diet a frequent factor. Frequently, hair may simply thin as a result of predetermined genetic factors, family history, and the overall aging process. Many men and women may notice a mild and often normal physiologic thinning of hair starting in their thirties and forties. Other times, normal life variations including temporary severe stress, nutritional changes, and hormonal changes like those in pregnancy, puberty, and menopause may cause a reversible hair loss.
Notably, several health conditions, including thyroid disease and iron deficiency anemia, can cause hair loss. While thyroid blood tests and other lab tests, including a complete blood count (CBC), on people who have ordinary hair loss are usually normal, it is important to exclude underlying causes in sudden or severe hair loss. If you are concerned about some other underlying health issues, you may start by seeing your family physician, internist, or gynecologist for basic health screening. Dermatologists are doctors who specialize in problems of skin, hair, and nails and may provide more advanced diagnosis and treatment of hair thinning and loss. Sometimes a scalp biopsy may be taken to help in diagnosis of severe or unexplained hair loss.
Although many medications list “hair loss” among their potential side effects, drugs are also not overall common causes of thinning or lost hair. On the other hand, with cancer treatments and immune suppression medications including chemotherapy, hair loss is a very common side effect. Complete hair loss often occurs after a course of major chemotherapy for cancer. Usually, hair regrows after six to 12 months.
