Hair loss can occur for a variety of reasons, including genetics, hormones, stress, and medical conditions. Alopecia is an umbrella term for any type of hair loss, whereas male pattern baldness is a specific type of hair loss that occurs in men and can be exacerbated by the use of male hormone replacement therapy. 

Male pattern baldness can begin as early as the late teens or early twenties, but most men start noticing signs in their 30s, with the most common onset age range being between the late 20s and early 30s. However, the exact timing can vary greatly between individuals, depending on genetics and other factors. 

Early signs often begin with a receding hairline or thinning hair on the crown of the head. Male pattern baldness is largely influenced by inherited genes. omit Hair loss can progress gradually over time, but some men experience more rapid hair loss than others.