1 Examples of trigger events include sudden or excessive weight loss, a high fever, surgery, or a death in the family.  Certain hairstyles and treatments. Excessive hairstyling or hairstyles that pull your hair tight, such as pigtails or cornrows, can cause traction alopecia.
http://www.mayoclinic.org/diseases-conditions/hair-loss/basics/causes/CON-20027666
1 Alopecia areata is a hair-loss condition which usually affects the scalp. 2  Alopecia areata causes one or more patches of hair loss. 3  Alopecia areata affects both genders.  It is an autoimmune disorder, in which the immune system attacks hair follicles, is believed to cause alopecia areata.
http://www.medicinenet.com/alopecia_areata/article.htm
Alopecia areata facts. 1  Alopecia areata is a hair-loss condition which usually affects the scalp. 2  Alopecia areata causes one or more patches of hair loss. 3  Alopecia areata affects both genders.  It is an autoimmune disorder, in which the immune system attacks hair follicles, is believed to cause alopecia areata.
http://www.medicinenet.com/alopecia_areata/article.htm
1 It is an autoimmune disorder, in which the immune system attacks hair follicles, is believed to cause alopecia areata. 2  For most patients, the condition resolves without treatment within a year, but hair loss is sometimes permanent.  A number of treatments are known to aid in hair regrowth.
http://www.medicinenet.com/alopecia_areata/article.htm
1 This type of hair loss is temporary. Examples of trigger events include sudden or excessive weight loss, a high fever, surgery, or a death in the family.  Certain hairstyles and treatments. Excessive hairstyling or hairstyles that pull your hair tight, such as pigtails or cornrows, can cause traction alopecia.
http://www.mayoclinic.org/diseases-conditions/hair-loss/basics/causes/CON-20027666
Alopecia is hair loss that can be caused by heredity, aging, disease, medications or lifestyle. The timing and course of hair loss can provide clues to its cause. For example, hair loss that comes on suddenly may be attributed to illness, diet, or medical treatments, such as chemotherapy or radiation.
http://www.healthgrades.com/conditions/alopecia
Sudden, drastic hair loss that occurs over a short period of time should be evaluated by your health care provider, as it can signal underlying disease. Alopecia areata is an autoimmune disease that causes the hair to fall out in patches. Another cause of hair loss is a condition called cicatricial alopecia, in which the hair follicles that produce hair are destroyed. Hair loss can be experienced by people with certain types of anemia, anorexia, and thyroid disease.
http://www.healthgrades.com/conditions/alopecia
1 Infections, such as ringworm, can invade the hair and skin of your scalp, leading to scaly patches and hair loss. Once infections are treated, hair generally grows back.  Other skin disorders. Diseases that cause scarring alopecia may result in permanent loss at the scarred areas.
http://www.mayoclinic.org/diseases-conditions/hair-loss/basics/causes/CON-20027666
1 Alopecia areata causes one or more patches of hair loss. 2  Alopecia areata affects both genders.  It is an autoimmune disorder, in which the immune system attacks hair follicles, is believed to cause alopecia areata.
http://www.medicinenet.com/alopecia_areata/article.htm
Family history (heredity) The most common cause of hair loss is a hereditary condition called male-pattern baldness or female-pattern baldness. It usually occurs gradually and in predictable patterns — a receding hairline and bald spots in men and thinning hair in women.
http://www.mayoclinic.org/diseases-conditions/hair-loss/basics/causes/CON-20027666
what causes alopecia in women
Heredity, aging, disease, medications or lifestyle causes alopecia in women. The causes of alopecia in women are heredity, aging, disease, medications, or lifestyle.