A tan is your skin’s reaction to the damage done by ultraviolet radiation.

Infrared radiation from the sun also can be harmful to the skin, increasing the risk of skin cancer and causing premature aging.

In North America, the peak hours of exposure to ultraviolet radiation are between 10:00 A.M. and 3:00 P.M.

The exposure to ultraviolet rays increases at higher altitudes and in regions where the ozone layer is thinner.

Many medicines, including certain antibiotics, can increase a person’s sensitivity to sunlight.

The chemicals in some perfumes also can heighten sensitivity to sunlight.

Symptoms of sunburn—such as reddened skin—can take up to 24 hours to appear.