This is the same condition that causes male pattern baldness. In women, the hair thinning is spread all over the scalp, while in men there is usually a more distinct thinning in one area of the scalp. Androgenetic alopecia occurs when testosterone is exposed to certain enzymes in hair cells and it is changed into one of the other androgens, dihydrotestosterone (DHT). If too much of this DHT builds up, the hair follicles shrink and the growth cycle of the hair is altered. In women, many of the follicles actually die and others become unable to produce new hair.
This type of hair loss in women can be caused by hairstyles like braids and ponytails that pull the hair too tightly across the scalp. This traumatizes the hair follicles enough to impede hair growth. This condition can be corrected by changing the hairstyle to something less restricting.
The hair has three phases in what is known as the growth cycle: the growth phase,the resting phase, and the shedding phase. After the resting phase, the body sheds some hair so that new hair growth can occur. Telogen effluvium is a condition that occurs when the body has experienced something so physically traumatic like giving birth, malnutrition, or a bad infection that most of the hair temporarily goes into the shedding phase. This can last several months to several years as long as the stress factors that caused in the first place are present.
This type of hair loss occurs when the hair follicles go through something that impedes its normal growth activity. A common example of this is chemotherapy, which can cause 90 percent of the hair to fall out.
The most common reason that women lose hair is due to change in the function of the thyroid brought on by menopause. Other things that can cause hair loss are changes in the levels of hormones, stress, certain medications, and heredity.