Illness, Emotional trauma, Protein deprivation (During strict dieting), and Hormonal changes like those in Pregnancy, Puberty, and Menopause may cause Hair loss. Several health conditions, including thyroid disease, iron deficiency anemia, and secondary syphilis, dandruff etc.
The most common cause of hair loss is a hereditary condition called male-pattern baldness or female-pattern baldness. It usually occurs gradually with aging and in predictable patterns a receding hairline and bald spots in men and thinning hair in women.
Hormonal imbalance Androgens (male hormones) are not very hair friendly, and can shorten the hair growth cycle. An excess of androgens (which could be caused by an endocrine disorder, such as Polycystic Ovarian Syndrome) can cause hair loss.