The most common cause of hair loss in men and women is genetic pattern hair loss, a hereditary condition that causes permanent hair loss. Aging also causes natural hair thinning. Medical conditions that can cause hair loss include thyroid disorders, lupus and scalp infections such as ringworm, according to the Mayo Clinic.
Sudden physical or emotional shock, such as extreme weight loss, childbirth, fever or the death of a loved one, can also cause general hair thinning. This thinning typically occurs several months after the traumatic event, explains the Mayo Clinic.
The use of certain medications can also cause hair loss. Prescription drugs used to treat high blood pressure, depression, heart problems, arthritis and cancer are known to cause hair thinning, states the Mayo Clinic.
The treatment for hair thinning depends on the cause. If an underlying disease is causing the hair loss, hair growth can be expected to resume when the disease is successfully treated. According to the Mayo Clinic, hereditary hair loss can be treated with minoxidil (Rogaine), a topical over-the-counter medication, and finasteride (Propecia), a prescription oral medication. Available in a 2- or 5-percent solution, minoxidil is applied to the scalp twice a day. Finasteride is for men only, and when taken once per day it can slow or stop the progression of male-pattern baldness.