The facts of sunburns

The Facts
Sunburn is a kind of radiation damage done by the sun. It's by far the most common form of radiation damage. While most people know radiation is dangerous, they voluntarily expose themselves to the harmful ultraviolet (UV) light of the sun on a regular basis.
Radiation can provoke cancer, and the popularity of sunbathing has brought a steady climb in new cases of skin cancer and actinic keratosis, a precursor to skin cancer. Actinic keratosis and all types of skin cancer, particularly nonmelanoma types (basal and squamous cell cancer), are directly linked to sun exposure. Exposure in early life is especially relevant. Many people get the bulk of their sun exposure during childhood, and it's been shown that even one childhood sunburn increases the risk of developing skin cancer later in life. However, sunburn is not required to damage skin. A tan is also clear evidence of UV skin damage.
In Canada, skin cancer is still fairly rare in people under 40. The amount of UV radiation is more variable in northern than southern latitudes, so the total dose received accumulates more slowly. In Australia, where people are exposed to far more UV light from an early age, skin cancer is a disease that more often strikes people in their 20s and 30s.
The depletion of the ozone layer has raised the degree of exposure, but not by as much as sun-worshipping habits. Regardless, the extra cancer cases from the ozone effect mostly haven't had time to develop yet.
If it weren't for skin cancer, sunburn would be a minor health problem, with only the most extreme cases requiring hospital treatment. As it is, any sun or other UV exposure, including a gentle tan, increases the risk of skin cancer.