Hair loss or baldness (technically known as alopecia) is a loss of hair from the head or body. Baldness can refer to general hair loss or androgenic alopecia (male/female pattern baldness). There ae different causes of alopecia and ae usually classified into cicatricial (scarring) alopecia and non-cicatricial alopecia (non-scarring). Causes of Hair loss include:

Androgenetic Alopecia (heredity)  

The most common cause of hair loss is a hereditary condition called male-pattern baldness or female-pattern baldness. It usually occurs gradually and in predictable patterns — a receding hairline and bald spots in men and thinning hair in women.

Heredity also affects the age at which you begin to lose hair, the rate of hair loss and the extent of baldness. Pattern baldness is most common in men and can begin as early as puberty. This type of hair loss may involve both hair thinning and miniaturization (hair becomes soft, fine and short).

Hormonal changes Hormonal changes and imbalances can cause temporary hair loss. This could be due to pregnancy, childbirth or the onset of menopause. Hormone levels are also affected by the thyroid gland, so thyroid problems may cause hair loss.

Patchy hair loss. This type of nonscarring hair loss is called alopecia areata  It occurs when the body's immune system attacks hair follicles — causing sudden hair loss that leaves smooth, roundish bald patches on the skin.

Scalp infections. Infections, such as ringworm, can invade the hair and skin of your scalp, leading to scaly patches and hair loss. Once infections are treated, hair generally grows back.

Other skin disorders. Diseases that cause scarring alopecia may result in permanent loss at the scarred areas. These conditions include lichen planus, some types of lupus and sarcoidosis.

Hair-pulling disorder. This condition, also called trichotillomania causes people to have an irresistible urge to pull out their hair, whether it's from the scalp, the eyebrows or other areas of the body.