“Androgenic (aka Male or female pattern) alopecia is related to sensitivity of the hair follicles to DHT, a breakdown product of testosterone). This type of hair loss is related to heredity, but can also be linked with ovarian cysts, certain birth control pills, pregnancy, and menopause.
Telogen Effluvium (or Traumatic hair loss) can occur after surgery, childbirth, severe infection, or even with severe stress. When this happens, the hairs that are in the active growth phase (usually about 90% of the hairs on the head) all go into the shedding phase at once, usually about 6-12 weeks after the stressful event. Most of the time, this will return to normal once the stressful episode is over, but occasionally it can persist for months or years.
Anagen Effluvium (or growth phase hair loss) is commonly seen after chemotherapy and is related to impairment of cell division in the hair follicle. Eventually the shaft of the hair narrows so much that the hair breaks before it reaches a visible length.
Traction alopecia is trauma to hair follicles from trauma over time related to braiding, tight ponytails, and extensions. Trauma from burns or other wounds can also result in patchy hair loss on the scalp.
Allopecia Areata is a condition which causes patchy hair loss on the scalp and eyebrows.
There are also other causes that are related to hormonal or nutritional imbalances, like hypothyroidism, medication side effects, and autoimmune disease, which may be correctable when the underlying cause is treated. ” – Answer provided by Dr. Dana Goldberg of Florida Plastic Surgery