The various causes / factors leading to hair loss include:
1) Skin diseases affecting the scalp like fungal infection of scalp known as tinea capitis, seborrhoea (dandruff), eczema of scalp, or lichen planus.
2) Genetic factors.
3) Hormonal changes including those that occur after childbirth and during menopause.
4) Nutritional deficiencies due to a diet that lacks iron (leading to anemia), and also lack of protein intake.
5) Recovery from acute fever like typhoid and erysipelas leads to diffuse hair loss.
6) Drug use like the ones that are used in treating high blood pressure, joint pains, cancer, or depression. Anagen effluvium refers to the condition of hair loss due to chemotherapy in a cancer patient.
7) Physical trauma / injury to head.
8) Emotional trauma like constant stress or grief due to loss of a family member / close friend.
9) General diseases like diabetes mellitus, tuberculosis, Hypothyroidism, or AIDS.
10) Auto-immune related hair loss in which the hair cells are mistaken for a foreign body and are destroyed by the immune cells of the body.
11) Hairstyles like tight braids or ponytails where the hair is tightly pulled backwards leading to traction alopecia; indiscriminate use of hair colors and hair straighteners.
12) Trichotillomania, which is a mental disorder in which the affected person voluntarily pulls out his / her scalp hair.