Male-pattern baldness is due in large part to an androgen (a so-called “male hormone") called dihydrotestosterone (DHT), which can sometimes contribute to female-pattern baldness as well. Other factors – like aging and genetics – can also increase the risk of male- and female-pattern baldness.
Alopecia areata is the result of the body's immune cells attacking hair follicles, resulting in inflammation and eventual hair loss.
Hair loss can also be the result of medical conditions, medications, and infection.