Most men—and some women—experience some degree of hair loss as they grow older. In the normal cycle of hair growth, it is natural to lose up to 100 hairs per day. If you are losing more than that, or if your hairline becomes more prominent, it could be a sign of excessive hair loss.
The medical term for hair loss is alopecia. The most common type of hair loss in men is male pattern baldness, or androgenic alopecia. This is an inherited tendency to stop producing new hairs. Each hair follicle produces a single hair that normally grows about a half inch per month for about 4 to 6 years. It then goes into a resting phase and loses the hair before growing a new one. The number of hair follicles entering the resting phase is equal to the number of hair follicles starting the growth phase, so the number of hairs on the head remains the same. With androgenic alopecia, an increasing number of hair follicles never recover from the resting phase, resulting in a scalp with less hair. This loss of active hair follicles may take place over months or years before it is noticeable. The hair follicles that usually stop producing new hairs are located along the frontal part of the scalp and along the crown of the head. This results in a receding hairline and/or balding at the top of the head.
Other causes of hair loss include:
Alopecia areata, an autoimmune disorder that attacks the hair follicles, shrinking them and inhibiting hair growth (can also lead to bald spots of facial hair)
Stressful events, such as major surgery
Medications that can damage hair follicles, such as chemotherapy or blood thinners