A 1. Normal variation. A hair's natural cycle is for it to grow for several years, then fall out and be replaced.
2. Hormonal abnormalities. A variety of hormonal problems are known to contribute to hair loss.
3. Scalp inflammation. Several inflammatory skin conditions, such as eczema, seborrhea, and psoriasis, cause patches of hair loss.
4. Excessive mental stress can also cause alopecia areata, telogen hair loss and other types of hair loss.
5. The side effect of drugs, such as chemotherapy drugs for malignant tumors can cause hair loss.