Causes of Hair Loss There are many different causes of hair loss.  These causes include:  serious illness, very high stress, crashes dieting, damaging hair care practice and most commonly alopecia areata. Alopecia Areata: A common cause of hair loss is an autoimmune disease called alopecia areata.  This condition affects both men and women of all races and ages.  It typically begins with one or more small patches. There can also be a thinning of hair over the entire head.  When all hair is lost from the entire scalp, the condition is called alopecia totalis.   In alopecia areata, a person’s immune system actually attacks hair follicles.  These follicles then shrink, slow production, and stop growing any visible hair.  This condition is most commonly found on the scalp. However, any place that grows hair can be affected. Research suggests that some people have genetic markers that increase their chances of developing alopecia areata.  These genetic markers also affect the amount of hair lost.  In one out of five people with alopecia areata, someone else in the family has it also.  Alopecia areata is often found in families with other autoimmune diseases like rheumatoid arthritis, Addison’s disease, early-onset diabetes, or thyroid disease. Inadequate diet: Such as one low in protein or a crash diet can cause hair loss.  The body will save internal protein by switching hair to the resting phase.  This results in hair loss tow to three months later.  The hair will usually grow back if the person goes back to a healthy diet. Stress: Can also speed or cause hair loss in both men and women.  Severe stress caused by severe illness, major surgery or the loss of a loved one may lead to hair loss.  Also, stress can increase the speed of the hair loss process of people who have genetically inherited the trait.  Elimination of stress factors can slow or even reverse some hair loss.