Hair loss is a common condition, but there are different forms of hair loss and a variety of possible causes. Common types of hair loss include male-pattern hair loss, female-pattern hair loss, androgenic baldness, telogen effluvium, and alopecia aerate. By the age of 50, pattern hair loss affects half of all men and around a quarter of women. 

Male-pattern baldness is caused by genetics and male hormones; alopecia aerate is an autoimmune condition; telogen effluvium is typically caused by physical or psychological stress. The cause of female-pattern baldness remains unclear. 

Hair loss may be a symptom of underlying medical conditions, such as thyroid disease, malnutrition, HIV, or lupus. It can also be a side effect of certain medical treatments, procedures, notably chemotherapy and radiation therapy; or medication, including certain anticoagulants.

Treatment options for hair loss are hair transplant surgery or medication. Drugs commonly used to treat hair loss are 5-alpha reductase inhibitors, such as finasteride. In the case of alopecia, steroid injections to the affected area may also be an option.