Sunburn is a form of radiation burn that affects living tissue, such as skin, that results from an overexposure to ultraviolet (UV) radiation, usually from the Sun. Common symptoms in humans and other animals include red or reddish skin that is hot to the touch or painful, general fatigue, and mild dizziness. Other symptoms include blistering, peeling skin, swelling, itching, and nausea. Excessive UV radiation is the leading cause of (primarily) non-malignant skin tumors,World Health Organization, International Agency for Research on Cancer "Do sunscreens prevent skin cancer" Press release No. 132, 5 June 2000World Health Organization, International Agency for Research on Cancer "Solar and ultraviolet radiation" IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 55, November 1997 which in extreme cases can be life-threatening. Sunburn is an inflammatory response in the tissue triggered by the nucleic acid damage caused by UV radiation.
Sun protective measures like sunscreen and sun protective clothing are widely accepted to prevent sunburn and some types of skin cancer. Special populations, including children, are especially susceptible to sunburn and protective measures should be used to prevent damage.
Signs and symptoms
Sunburn will show as varying degrees of skin redness (erythema) and swelling, depending on the extent and severity of sun exposure. Severe sunburn can cause blistering, itching, peeling skin, rash, and even nausea, fever, chills, and fainting, and so is sometimes informally termed sun poisoning. Capillaries close to the sunburned skin surface produce heat, making the affected area warm to the touch. Sunburns may be classified as superficial or partial-thickness burns. Blistering is a sign of second-degree sunburn.
Variations Minor sunburns typically cause nothing more than slight redness and tenderness to the affected areas. In more serious cases, blistering can occur. Extreme sunburns can be painful to the point of debilitation and may require hospital care.
Duration Sunburn can occur in less than 15 minutes in response to sun exposure. However, the first signs of damage may not appear for a few hours. Sunburn can occur in seconds when exposed to non-shielded welding arcs or other sources of intense ultraviolet light.
Sunburn symptoms are typically at their worst 24 to 36 hours after sun exposure and usually begin to improve after 3 to 5 days. After a few days, the skin may start to flake and peel, with full healing typically occurring within 7 days. Small amounts of skin may continue to peel for days or even weeks after.
Skin cancer Ultraviolet radiation causes sunburns and increases the risk of three types of skin cancer: melanoma, basal-cell carcinoma and squamous-cell carcinoma."Facts About Sunburn and Skin Cancer" , Skin Cancer Foundation Of greatest concern is that the melanoma risk increases dose-dependently proportional to the number of a person's lifetime cumulative episodes of sunburn. An estimated 1/3 of melanomas in the United States and Australia could be prevented with regular sunscreen use.
Mechanism Sunburn is caused by prolonged exposure to ultraviolet radiation from the Sun or artificial sources such as tanning lamps, welding arcs, or ultraviolet germicidal irradiation. Two types of ultraviolet radiation from the Sun reach the Earth’s surface, UVA and UVB. UVA is 1,000–2,000 times less effective at causing sunburn than UVB, as it has less energy.
UVB damages mRNA. This triggers a fast pathway that leads to inflammation of the skin, and sunburn. mRNA damage initially triggers a response in ribosomes through a protein known as ZAK-alpha in a stress response. This response acts as a cell surveillance system. Following this, detection of RNA damage leads to inflammatory signaling and recruitment of immune cells. RNA damage, but not DNA damage, results in UVB induced skin inflammation and acute sunburn.
The stress also triggers several defense mechanisms, including DNA repair to revert the damage, apoptosis and peeling to remove irreparably damaged skin cells, and increased melanin production to prevent future damage.
Melanin readily absorbs UV wavelength light. By preventing UV photons from disrupting chemical bonds, melanin inhibits both the direct alteration of DNA, as well as the generation of free radicals, to prevent them from indirectly damaging DNA. However, human melanocytes contain over 2,000 genomic sites that are highly sensitive to UV, and such sites can be up to 170-fold more sensitive to UV induction of cyclobutane pyrimidine dimers than the average site.
Sunburn causes an inflammation process that includes the production of prostanoids and bradykinin. These chemical compounds increase sensitivity to heat by reducing the threshold of heat receptor (TRPV1) activation from to . The pain may be caused by the overproduction of a protein called CXCL5, which activates nerve fibers.
Risk factors The most significant risk factor for sunburn is the duration and intensity of UV exposure to the skin. The face, neck and trunk are two to four times more sensitive than the extremities. Additionally, individuals with lighter skin tones or those on specific medications are more susceptible to experiencing sunburn.
UV intensity The UV Index indicates the risk of sunburn at a given time and location. Contributing factors include: The time of day. In most locations, the sun's rays are strongest between approximately 10 am and 4 pm daylight saving time. Cloud cover. Clouds partially block UV, but even on an overcast day, a significant percentage of the sun's damaging UV radiation can pass through clouds. Proximity to reflective surfaces, such as water, sand, concrete, snow, and ice. All of these reflect the sun's rays and can cause sunburns. The season of the year. The Sun's position in late spring and early summer can cause a more-severe sunburn. Altitude. At a higher altitude, it is easier to become burnt, because there is less of the Earth's atmosphere to block the sunlight. UV exposure increases about 4% for every 1000 ft (305 m) gain in elevation. Proximity to the equator (latitude). Between the polar and tropical regions, the closer to the equator, the more direct sunlight passes through the atmosphere over a year. For example, the southern United States gets fifty percent more sunlight than the northern United States.
Because of variations in the intensity of UV radiation passing through the atmosphere, the risk of sunburn increases with proximity to the tropic latitudes, located between 23.5° north and south latitude. All else being equal (e.g., cloud cover, ozone layer, terrain, etc.), each location within the tropic or polar regions receives approximately the same amount of UV radiation over a year. In the temperate zones between 23.5° and 66.5°, UV radiation varies substantially by latitude and season. The higher the latitude, the lower the intensity of the UV rays. Sun intensity in the northern hemisphere is greatest during May, June and Julyand in the southern hemisphere, November, December and January. On a minute-by-minute basis, the amount of UV radiation depends on the Sun's angle. Ultraviolet radiation is easily determined by the height ratio of any object to the size of its shadow. Height is measured parallel to the Earth's gravitational field and the projected shadow is measured on a flat, level surface. For objects wider than skulls or poles, the height and length are best measured relative to the same occluding edge. The most significant risk is at solar noon when shadows are at their minimum, and the Sun's radiation passes most directly through the atmosphere. Regardless of one's latitude (assuming no other variables), equal shadow lengths mean equal amounts of UV radiation.
The skin and eyes are most sensitive to damage by UV at 265–275 nm wavelength, which is in the lower UVC band that is rarely encountered except from artificial sources like welding arcs. Longer wavelengths of UV radiation cause most sunburn because those wavelengths are more prevalent in ground-level sunlight.
Skin type Skin type determines the ease of sunburn. People with lighter skin tones and limited capacity to develop a tan after UV radiation exposure have a greater risk of sunburn. Fitzpatrick's skin phototype system describes the normal variations of human skin responses to doses of UVB radiation. Persons with type I skin have the greatest capacity to sunburn, and type VI have the least capacity to burn. However, all skin types can develop sunburn or skin cancer.
Fitzpatrick's skin phototypes are as follows: Type 0: Albino. Type I: Pale light skin, burns easily, does not tan. Type II: Light skin, burns easily, tans with difficulty. Type III: Light beige skin, may burn, but eventually tans easily. Type IV: Light brown skin, hardly burns, tans easily. Type V: Brown skin, usually does not burn, tans easily. Type VI: Dark brown skin, very unlikely to burn, becomes darker with UV radiation exposure.
Tanning Suntans, which naturally develop in some individuals as a protective mechanism against the sun, are viewed by most in the Western world as desirable. Tanning has led to an increased exposure to UV radiation from both the natural sun and tanning lamps. Suntans can provide a modest sun protection factor (SPF) of 3, meaning that tanned skin would tolerate up to three times the UV exposure as pale skin.
Sunburns associated with indoor tanning can be severe. The World Health Organization, American Academy of Dermatology, and the Skin Cancer Foundation have recommended avoiding artificial UV sources such as tanning beds. Suntans are not recommended as a form of sun protection.
Ozone depletion In recent decades, the incidence and severity of sunburn have increased worldwide, partly because of chemical damage to the atmosphere's ozone layer. Between the 1970s and the 2000s, average stratospheric ozone decreased by approximately 4%, contributing an approximate 4% increase to the average UV intensity at the Earth's surface. Ozone depletion and the seasonal "ozone hole" have led to much larger changes in some locations, especially in the southern hemisphere.
Medication The risk of sunburn can be increased by pharmaceutical products that sensitize users to UV radiation. Certain antibiotics, oral contraceptives, antidepressants, acne medications, Anticonvulsants, Antipsychotics and Mood stabilizers have this effect."Avoiding Sun-Related Skin Damage". Fact-Sheets.com. 2004. Retrieved 3 January 2015.
Other factors Age also affects how skin reacts to the sun. Children younger than six and adults older than sixty are more sensitive to sunlight.
Certain genetic conditions, for example, xeroderma pigmentosum, increase a person's susceptibility to sunburn and subsequent skin cancers. These conditions involve defects in DNA repair mechanisms which decrease the ability to repair DNA damaged by UV radiation.
Diagnosis The differential diagnosis of sunburn includes other skin pathology induced by UV radiation, including photoallergic reactions, phototoxic reactions to topical or systemic medications, and other dermatologic disorders that are aggravated by exposure to sunlight. Considerations for diagnosis include duration and intensity of UV exposure, topical or systemic medication use, history of dermatologic disease, and nutritional status. Phototoxic reactions: Non-immunological response to sunlight interacting with certain drugs and chemicals in the skin which resembles an exaggerated sunburn. Common medications that may cause a phototoxic reaction include amiodarone, dacarbazine, fluoroquinolones, 5-fluorouracil, furosemide, nalidixic acid, phenothiazines, psoralens, retinoids, sulfonamides, sulfonylureas, tetracyclines, thiazides, and vinblastine.