When human skin peels, it is because dead skin cells are shedding. Suntans come from exposure to ultraviolet rays, which most people get from the sun. In response to ultraviolet ray exposure, special cells in the skin produce more of the pigment melanin as a protection against the harmful effects of ultraviolet rays.
Melanin is what darkens the skin, producing a suntan.
The skin can only produce a certain amount of melanin each day, so there is a limited amount of tanning that can be acquired. Overexposure to the sun may cause a sunburn, premature aging of the skin, dryness, and skin cancer. Skin cells are destroyed and there can be damage to the blood vessels underneath the skin. Worry about skin cancer doesn't usually tend to begin until a person is middle age because that is when changes in the skin become more noticeable. Although it is never too late to begin protecting oneself from too much ultraviolet ray exposure, unfortunately by middle age most of the sun damage is already done.