Answer:
There are multiple things that can cause Alopecia. Most common are:
-A diet lacking esencial nutrients.
-Thyroid Problems.
-Infections.
-Stress.
-Cosmetic Excesses or side effects of some treatments.
-Genetics (Androgenic Alopecia)
The most common in men is Androgenic Alopecia.
9 of 10 men older than 21 years present some type of recession on the hairline.
5 of 10 men older than 40 have the the crown affected.