Sunburn is a form of radiation burn affecting living tissue, most commonly skin, caused by overexposure to ultraviolet radiation, primarily from the Sun. The most familiar symptoms include reddened skin that is hot to the touch and painful, general fatigue, and mild dizziness. More severe cases can involve blistering, peeling, swelling, itching, and nausea. Excessive UV exposure is the leading cause of skin tumors, which are most often non-malignant but can in extreme cases become life-threatening. At the cellular level, sunburn is an inflammatory response triggered by the damage UV radiation inflicts on nucleic acids.

Protective measures including sunscreen and UV-blocking clothing are broadly recognized as effective in preventing sunburn and reducing the risk of certain skin cancers. Children and other populations with heightened sensitivity require particular attention to sun protection.

Sunburn is remarkably common, especially among younger people. In the United States, close to seventy-five percent of adolescents and young adults have experienced sunburn, and in northern European countries the figure exceeds fifty percent.

The long history of sun exposure across different climates has left a mark on human biology. People living in regions with intense, prolonged sunlight fared better with higher melanin concentrations, which provide natural resistance to burning, and natural selection reinforced those traits over generations.

One counterintuitive fact about sunburn is that the immediate pain and inflammation are triggered by damage to RNA rather than DNA. DNA damage is what produces the long-term mutations associated with cancer risk, but the body’s acute inflammatory reaction is a response to disrupted RNA.

Overcast conditions offer much less protection than most people assume. Up to eighty percent of UV radiation can pass through cloud cover, meaning the risk of burning on a cloudy day is nearly as high as on a clear one. The absence of heat from direct sunlight often leads people to underestimate how long they have been exposed.

A tan and a sunburn are fundamentally different biological events. Tanning is the skin’s attempt to defend itself by producing more melanin. Burning is direct inflammatory damage. A sunburn does not convert into a tan, and whatever temporary protection a resulting tan provides is equivalent to roughly SPF 2.

Skiers and winter outdoor enthusiasts face a significant and often underappreciated UV risk. What is commonly attributed to windburn on slopes is frequently sunburn caused by UV radiation reflected off snow and ice, which can bounce back up to eighty percent of incoming rays. Cold temperatures mask the warmth associated with sun exposure, making it easier to stay out longer without realizing the damage being done.

The full extent of a sunburn is not visible immediately after exposure. It can take up to twenty-four hours for redness to reach its peak, and pain typically intensifies somewhere between six and forty-eight hours after the exposure occurred.

Several ancient civilizations incorporated the sun’s power into their religious practices, including its capacity to harm. The Aztecs believed their sun deity Tonatiuh required a constant supply of human blood to complete his journey across the sky each day, and human sacrifice was conducted to meet that need. The Inca similarly offered sacrifices to their sun god Inti during times of crisis to maintain cosmic order. Ancient Egypt, by contrast, developed sophisticated approaches to protecting the body from solar rays rather than treating the sun’s destructive force as something to be appeased through ritual.

Animals are not immune to sunburn, particularly those with thin skin, sparse hair, or light pigmentation. Pigs, elephants, rhinos, hairless cats, and light-colored pets with pink ears and noses are all vulnerable. Even whales can sustain UV damage when they spend extended time near the ocean’s surface. Some species have evolved effective natural defenses. Hippos secrete a reddish oily substance from their skin that functions as a natural sunscreen. Giraffes possess darkly pigmented tongues that resist UV damage. Many birds, reptiles, and fish produce a compound called gadusol that provides built-in UV protection. No animal is entirely immune, but these adaptations give certain species a meaningful advantage when it comes to tolerating solar exposure.