In the past, sun exposure was thought to be a healthy benefit of outdoor activity. Modern scientific information, however, has shown many unhealthy effects of sun exposure, such as early aging of the skin and skin cancer.
Sunburn is a visible type of damage, which appears just a few hours after sun exposure.
In many people, this type of damage also causes tanning. Freckles, which occur in people with fair skin, are usually due to sun exposure. Freckles are nearly always a sign that sun damage has occurred, and therefore show the need for sun protection. Ultraviolet light rays also cause invisible damage to skin cells. Some of the injury is repaired, but some of the cell damage adds up year after year.