Sunburn is a kind of radiation damage done by the sun. While most people know that 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 non-melanoma 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 has 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.
Sun exposure and sunburn in particular also contribute to photoaging, or the appearance of aging and wrinkled skin. Most of the wrinkles and pigmentation problems seen in the elderly are a direct result of cumulative sun exposure.
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.