Sunburn results from a brief (acute) overexposure to ultraviolet (UV) light. The amount of sun exposure required to produce a burn varies with the amount of melanin in the skin (usually visible as the amount of pigmentation), the ability to produce more melanin, and the amount of UV light in the sunlight on the day of overexposure.
Sunburn results in painful reddened skin. Severe sunburn may cause swelling and blisters. Symptoms may begin as soon as 1 hour after exposure and typically reach their peak within 3 days (usually between 12 hours and 24 hours). Some severely sunburned people develop a fever, chills, and weakness and on rare occasions even may go into shock (characterized by very low blood pressure, fainting, and profound weakness). Several days after a sunburn, people with naturally fair skin may have peeling in the burned area, usually accompanied by itching. These peeled areas are even more sensitive to sunburn for several weeks. Sunburned skin, particularly peeled sunburned skin, can become infected. The skin may become permanently blotchy. People who have had severe sunburns when young are at greater risk of skin cancer in later years, even if they have not been exposed to too much sun since that time.
The best—and most obvious—way to prevent sun damage is to stay out of strong, direct sunlight. Exposure to bright midday sun should be minimized (30 minutes or less), even for people with dark skin. UV rays are not as strong before 10 am and after 3 pm. If sun exposure is unavoidable, the person should seek shade as soon as possible, cover up in UV-protective clothing, and wear sunscreen, a hat, and UV-protective sunglasses. Many materials are capable of filtering or blocking UV radiation, but many are not. Clothing, ordinary window glass, smoke, and smog filter out most of the damaging rays. However, water is not a good filter. UVA and UVB light can penetrate a foot (about 30 centimeters) of clear water. Clouds and fog are also not good filters of UV light—a person can get sunburned on a cloudy or foggy day. Snow, water, and sand reflect sunlight, magnifying the amount of UV light that reaches the skin. People also burn more quickly at high altitudes, where the thin air allows more burning UV light to reach the skin, and low latitudes (such as at the equator).
The sun's damaging effects can be further minimized by wearing protective coverings such as hats, shirts, pants, and sunglasses. Fabrics with a tight weave block the sun better than fabrics with a loose weave. Special clothing that provides high sun protection is commercially available. This type of clothing is labeled with ultraviolet protection factor (UPF) followed by a number that indicates the level of protection (similar to sunscreen labeling). Broad-brimmed hats help protect the face, ears, and neck, but people still need to apply sunscreen to these areas. People should regularly wear UV-protective, wrap-around sunglasses to help shield the eyes and eyelids.
Before exposure to strong direct sunlight, a person should apply a sunscreen, which is an ointment or cream containing chemicals that protect the skin by filtering out UV light. Older sunscreens tended to filter only UVB light, but many newer sunscreens effectively filter UVA light as well.
Sunscreens are available in a wide variety of formulations, including creams, gels, foams, sprays, and sticks. Self-tanning products do not provide significant protection from UV exposure.
Sunscreens contain substances, such as para-aminobenzoic acid (PABA) and benzophenones (such as avobenzone), which absorb UV light. Because PABA does not immediately bind strongly to the skin, sunscreens containing PABA must be applied 30 minutes before going out in the sun or into the water. PABA may irritate the skin or cause an allergic reaction in some people. PABA and some other sunscreens block mostly UVB light, but benzophenones block UVA and UVB light. Many sunscreens contain both PABA and benzophenone or other chemicals and provide protection against UVA and UVB light.
Other sunscreens, called sunblocks, contain physical barriers such as zinc oxide or titanium dioxide. These thick, white ointments block almost all sunlight from the skin and can be used on small, sensitive areas, such as the nose and lips. Some cosmetics contain zinc oxide or titanium dioxide. Newer-formulated sunblocks have a more pleasing thickness and color, which allow them to be combined with other traditional chemical blockers thereby providing even more sun protection to a given formulation.
In the United States, the Food and Drug Administration (FDA) rates sunscreens by their sun protection factor (SPF) number—the higher the SPF number, the greater the protection. Sunscreens rated between 2 and 12 provide some protection; those rated between 13 and 29 provide good protection; those rated 30 and above provide maximum protection. The FDA is changing the way sunscreen manufacturers are required to label their products. Products that protect against all sun-induced skin damage will be labeled broad spectrum and have an SPF of 15 (or higher). The SPF, however, only quantifies the protection against UVB light exposure; there is no scale for UVA light protection. For the best protection, people should usually use sunscreen with an SPF rating of 50 or higher.
Sunscreens can fail if not enough of the product is applied, if the product is applied too late (sunscreens should optimally be applied 30 minutes before exposure to the sun), and if the product is not reapplied after swimming or sweating (even sunscreens labeled as waterproof or water-resistant), or after every 2 hours during sun exposure.
Sometimes sunscreens cause allergic reactions. People may react to the sunscreen after applying it or after applying it and then going in the sun (called a photoallergic reaction). Some dermatologists can do tests to diagnose such reactions if the reason for the reaction is unclear (see Sunlight and Skin Damage: Photosensitivity Reactions).
Cold-water compresses can soothe raw, hot areas, as can aloe vera, petrolatum-based products such as petroleum jelly, and skin moisturizers without anesthetics or perfumes that might irritate or sensitize the skin. Nonsteroidal anti-inflammatory drugs (NSAIDs—see Pain: Nonsteroidal Anti-Inflammatory Drugs) help relieve pain and inflammation. Ointments or lotions containing anesthetics (such as benzocaine and diphenhydramine) temporarily relieve pain but should be avoided because they occasionally trigger an allergic reaction. Corticosteroid tablets also may help relieve the inflammation but are used only for the most serious burns. Specific antibiotic burn creams are required only for severe blistering. Most sunburn blisters break on their own and do not need to be popped and drained. Sunburned skin rarely becomes infected, but if an infection develops, healing may be delayed. A doctor can determine the severity of an infection and prescribe antibiotics if necessary.
Sunburned skin begins healing by itself within several days, but complete healing may take weeks. After burned skin peels, the newly exposed layers are thin and initially very sensitive to sunlight and must be protected for several weeks.
Last full review/revision December 2012 by Robert J. MacNeal, MD