Losing up to 100-150 hairs per day is normal. In general, most hair loss is not associated with systemic or internal disease, nor is poor diet a frequent factor. Frequently, hair may simply thin as a result of predetermined genetic factors, family history, and the overall aging process. Many men and women may notice a mild and often normal physiologic thinning of hair starting in their thirties and forties. 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.