Sunburn

Sunburn is an inflammatory response to ultraviolet injury in the epidermis, the skin’s outermost layer. UVB is the principal wavelength responsible for visible burning, while UVA penetrates more deeply and contributes to oxidative damage, photoaging and some aspects of cancer risk.¹ Damaged skin cells release chemical signals that widen nearby blood vessels and recruit immune cells, producing redness, heat, swelling and tenderness.

The injury begins before it becomes visible. Ultraviolet radiation can alter cellular DNA and trigger programmed cell death; peeling later removes some of these damaged cells but does not erase the underlying exposure. Skin pigmentation offers partial protection because melanin absorbs and scatters radiation, yet people of every skin tone can burn and can develop UV-related skin disease.²

Sunburn usually appears within a few hours and often becomes most painful and intensely red during the following day. Mild burns cause erythema, warmth, tightness and pain; more severe burns may produce fluid-filled blisters, marked swelling, headache, nausea, fever or chills.³

Blistering indicates a deeper partial-thickness injury and warrants more cautious care. Extensive burns, burns in infants, dehydration, confusion, fainting, persistent vomiting or signs of infection require medical assessment. Severe exposure can occur alongside heat illness, but sunburn itself is not heatstroke. Repeated burns, particularly during childhood and adolescence, are associated with increased lifetime risk of melanoma and other skin cancers.⁴

First aid centers on stopping further exposure, cooling the skin gently and replacing lost fluids. Cool, damp compresses, a lukewarm bath, loose clothing and fragrance-free moisturizer can reduce discomfort; oral pain relievers may help when they are safe for the individual. Blisters should not be deliberately opened, and peeling skin should not be pulled away.³

Prevention combines shade, protective clothing, a broad-spectrum sunscreen and avoidance of deliberate tanning. Sunscreen should be applied generously and reapplied after swimming, sweating or towel drying; it supplements rather than replaces clothing and shade. The UV Index communicates the expected intensity of ultraviolet radiation and helps guide protective decisions, including on cool or cloudy days.¹

Sunburn risk depends on more than temperature or visible brightness. Snow, sand and water can reflect ultraviolet radiation, altitude can increase exposure, and clouds may reduce but do not eliminate it. A person can therefore burn during winter sports, boating or overcast outdoor activities.¹

Some medicines and plant chemicals produce photosensitivity, making ordinary exposure unusually damaging; examples include certain antibiotics, diuretics and topical products, although the risk varies by substance. A separate reaction called phytophotodermatitis can follow contact with plant compounds such as furocoumarins and subsequent sunlight exposure, creating painful, burn-like streaks that are not ordinary sunburn. Darker skin reduces—but does not eliminate—the chance of burning, and redness may be harder to see, so pain, warmth, swelling and peeling remain useful warning signs.²⁵

Ultraviolet radiation

Invisible electromagnetic radiation from the Sun; UVB is the main cause of sunburn, while UVA contributes substantially to photoaging and cellular damage.

Erythema

Redness of the skin caused by increased blood flow, including the redness characteristic of sunburn.

Photosensitivity

An increased skin reaction to ultraviolet or visible light caused by a substance, medical condition or treatment.

UV Index

A standardized scale describing the intensity of sunburn-producing ultraviolet radiation at a particular place and time.