Usually there is a history of recent sun exposure, outdoor activity or use of indoor tanning equipment. Skin redness develops after two to six hours and peaks at 12-24 hours. The reddened areas are usually painful and may blister.
In severe cases there is fever with nausea or vomiting. In most cases symptoms settle within seven to 10 days. In rare cases, sunburn may be so severe and diffuse that it results in second-degree burns, dehydration, secondary infection, shock or even death.
Lighter-skinned patients are affected more frequently and severely.
Morbidity and mortality associated with long-term sun exposure is related primarily to the development of cutaneous neoplasms: basal cell carcinoma, squamous cell carcinoma and malignant melanoma.
Factors increasing the risk
UV radiation penetrates moist skin more effectively than dry skin. Water is not a good filter: UVA and UVB light can penetrate a foot of clear water.
Clouds and fog are also not good filters of UV light. A person can become sunburnt on a cloudy or foggy day.
Snow and sand reflect sunlight, magnifying the amount of UV light that reaches the skin.
Radiation is 80 per cent reflected by snow and ice, compared with 20 per cent by sand.
People also burn more quickly at high altitudes, where the thin air allows more burning UV light to reach the skin. UV radiation increases 4 per cent for every 300m (1,000ft) increase in elevation.
There is more risk of sunburn on the limbs than on the face, neck and trunk.
The time of day is important because 65 per cent of UV radiation reaches the earth between 10am and 2pm.
The best way to prevent sun damage is to stay out of strong, direct sunlight.
Hats with brims, sunglasses with 99-100 per cent UV protection and protective clothing are essential if it is necessary to go out in direct strong sunlight.
Before exposure to strong direct sunlight, it is advisable to apply a sunscreen.
Most sunscreens tend to filter only UVB light, although some newer sunscreens are somewhat effective at filtering UVA light as well.
Sunscreens contain substances, such as para-aminobenzoic acid (PABA) and benzophenone, that absorb UV light.
Because PABA does not immediately bind strongly to the skin, sunscreens containing PABA must be applied 30 to 45 minutes before going out in the sun or into the water.
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 also contain zinc oxide or titanium dioxide. Sunscreens with SPF15 or higher are advised.
Patients should be advised to stay in a shaded, cool environment with bed rest as necessary and to drink plenty of water. Cool baths or cool tap water (depending on the affected surface area) or normal saline compresses for 20 minutes, repeated three to four times daily, may offer some relief from pain and pruritus. Applying calamine lotion three times daily to affected areas may help.
Moisturisers, applied liberally and frequently, help reduce dryness and peeling in mild sunburns. Bath preparations (for example colloidal oatmeal) are helpful, but direct patients to use soaps sparingly.
Most cases of sunburn are self-limiting. NSAIDs can help relieve pain and inflammation.
Specific antibiotic burn creams are required only for severe blistering.
Most sunburn blisters break on their own: they do not need to be drained since this increases the risk of infection.
Severe sunburn requires admission to a burns unit for parenteral fluid replacement, pain control, and prophylaxis against infection. Referral to an eye specialist is needed if corneal injury is suspected.
In a few patients there is a severe reaction to sunlight where there has been minimal exposure. In these cases it is wise to consider whether medication or an underlying medical condition may be causing the problem.
In some cases patients may not have been warned that their medication will make them unduly sun-sensitive.
Dr Merriman is a GP in Oxford
- http://dermnetnz.org. Covers all aspects of dermatology.
- NHS Direct. 'Sunburn': www.nhsdirect.nhs.uk
- Health Protection Agency. 'Solar index and skin type': www.hpa.org.uk
- SunSmart: http://info.cancerresearchuk.org/healthyliving/sunsmart/