Involutional Alopecia: a natural condition where the hair thins gradually with age. In this type of alopecia, an increased number of hair follicles go into the resting phase. The remaining hairs become shorter and fewer in number.

Androgenic Alopecia: a genetic condition that affects both men and women.
In men, this condition, often called male-pattern baldness, can begin as early as their teens or twenties. A receding hairline and a gradual loss of hair from the crown and frontal scalp characterize it.

In women, this condition, often called female-pattern baldness, causes noticeable hair thinning until their 40s or later. Typically, women experience a general thinning over their entire scalp, usually the most extensive hair loss is at the crown.