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Both emotional and physical stress (such as a serious illness or recovery from surgery) have been associated with hair loss. It is possible that stress induces hormonal changes that are responsible for the hair loss, since hair loss is a known consequence of other hormonal changes due to pregnancy, thyroid disturbances, or even from taking oral contraceptives.
Nervous habits, such as scalp rubbing or hair twisting or pulling may also be responsible for hair loss. These habits may be responses to psychological stress in some people and may be another cause of stress-related hair loss. Excessive hair-pulling is a form of impulse-control disorder medically referred to as trichotillomania.
The hair loss from hormonal changes often disappears after a period of months to two years. As with other stress-related symptoms, learning and practicing effective stress-management techniques can help reduce the severity of the symptoms.
"Evaluation and diagnosis of hair loss"