|photo credit: hair loss dot org|
Alopecia areata - This is also known as patchy hair loss. It occurs when the body's immune system attacks hair follicles causing sudden hair loss. On the other hand, other skin disorders like lichen planus, some types of lupus and sarcoidosis cause permanent hair loss.
Scalp infections - Infections such as ringworm can invade the hair and skin of your scalp. Generally, hair grows back as soon as the infections are treated.
Trichotillomania - This condition happens when a person has an overwhelming urge to pull out her hair. It can be the hair from her scalp, eyebrows or other areas of the body.
Medications - Drugs used for cancer, arthritis, depression, heart problems, high blood pressure and birth control can cause hair loss. Overdose of vitamin promotes hair loss too.
Other causes - radiation therapy, physical shock like surgery and excessive weight loss, emotional shock like death, hair treatments, excessive hairstyling, etc.
As for hair loss treatment, this video could give you a great idea about what you need to do.
(Note: I don't own this video. All credits to the owner/publisher.)