Healthy adults normally shed 50 -100 hairs each day. Temporary hair loss can occur due to stress, illness, thyroid disorder, kidney deficiency, hormonal imbalance and as a reaction to general anaesthetics and other medications. In these circumstances, a large number of hair follicles suddenly go into a resting phase, causing hair to thin noticeably, although the hair may not fall out until 2-3 months after the event. Hair loss can also be caused by exposure of the hair or scalp to burns, genetics, x-rays, scalp injury, infection, long term illnesses, side effects of medications, poor nutrition and certain chemicals (including those used to purify swimming pools, and to bleach, dye, and perm hair). Normal hair growth usually returns once the cause is eliminated. Dietary mineral deficiencies have also been implicated in hair loss, particularly deficiency of zinc, selenium, silica and copper and iron deficiency.