A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet (UV) radiation, commonly from the sun's rays. Usually, normal symptoms in humans and other animals consist of red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV radiation can be life-threatening in extreme cases. Exposure of the skin to lesser amounts of UV radiation will often produce a suntan.
Excessive UV radiation is the leading cause of primarily non-malignant skin tumors.[1][2] Sunscreen is widely agreed to prevent sunburn, although some scientists argue that it may not effectively protect against malignant melanoma, which either is caused by a different part of the ultraviolet spectrum or is not caused by sun exposure at all.[3][4] Clothing, including hats, is considered the preferred skin protection method. Moderate sun tanning without burning can also prevent subsequent sunburn, as it increases the amount of melanin, a skin photoprotectant pigment that is the skin's natural defense against overexposure. Importantly, both sunburn and the increase in melanin production are triggered by direct DNA damage. When the skin cells' DNA is damaged by UV radiation, type I cell-death is triggered and the skin is replaced.[5] Malignant melanoma may occur as a result of indirect DNA damage if the damage is not properly repaired. Proper repair occurs in the majority of DNA damage. The only cure for sunburn is slow healing, although some skin creams can help with the symptoms.
Sunburn is caused by UV radiation, either from the sun or from artificial sources, such as welding arcs, the lamps used in sunbeds, and ultraviolet germicidal irradiation. It is a reaction of the body to the direct DNA damage, which can result from the excitation of DNA by UV-B light. This damage is mainly the formation of a thymine dimer. The damage is recognized by the body, which then triggers several defense mechanisms, including DNA repair to revert the damage and increased melanin production to prevent future damage. Melanin transforms UV-photons quickly into harmless amounts of heat without generating free radicals, and is therefore an excellent photoprotectant against direct and indirect DNA damage.
The pain may be caused by overproduction of a protein called CXCL5, which activates nerve fibres[6].
Experiments with mice found that protection against sunburn by chemical sunscreens does not necessarily provide protection against other damaging effects of UV radiation such as enhanced melanoma growth.[7]
Ultraviolet B (UVB) radiation causes dangerous sunburns and increases the risk of two types of skin cancer: basal-cell carcinomaand squamous cell carcinoma.[1][2]
Some exposure to sunlight is not only harmless but positively necessary to health. Humans need vitamin D; most is synthesised in the body by exposure of the skin to sunlight, with some from the diet. People with darker skins need more sunlight to maintain vitamin D levels. The widespread concern about over-exposure to the sun causing cancer has led some people to go too far in avoiding exposure and using sunscreen; this can lead to vitamin D deficiency and the condition of rickets due to this deficiency, particularly in children, and particularly in climates with less sunshine. Cases of rickets are, indeed, on the increase. Twenty to thirty minutes of unimpeded exposure to the sun two to three times a week are recommended. [8]
[edit]Controversy over sunscreen
The statement sunburn causes skin cancer is considered accurate when it refers to either basal-cell carcinoma, the mildest form of cancer, or squamous cell carcinoma. However, this may be misleading when it comes to malignant melanoma (see picture: UVR sunburn melanoma)[citation needed]. The statistical correlation between sunburn and melanoma is assumed to be due to a common cause — UV radiation. Instead, this correlation may be generated via different mechanisms. Direct DNA damage is ascribed by many medical doctors to a change in behaviour of the sunscreen user due to a false sense of security afforded by the sunscreen. While some researchers believe that these confounding factors can be controlled for effectively, [9] others believe there to be insufficient correction for light-skinned individuals and indirect DNA damage.[clarification needed]
Topically applied sunscreen blocks UV rays as long as it does not penetrate into the skin. This prevents sunburn, suntanning, and skin cancer. If the sunscreen filter is absorbed into the skin, it prevents sunburn, but increases the amount of free radicals, which in turn increases the risk for malignant melanoma. The harmful effect of photo-excited sunscreen filters on living tissue has been shown in many photo-biological studies.[10][11][12][13] Whether sunscreen prevents or promotes the development of melanoma depends on the relative importance of the protective effect from the topical sunscreen versus the harmful effects of the absorbed sunscreen.
The use of sunscreen is known to prevent the direct DNA damage that causes sunburn and the two most common forms of skin cancer, basal-cell carcinoma and squamous cell carcinoma.[14] However, if sunscreen penetrates into the skin, it promotes indirect DNA damage, which causes the most lethal form of skin cancer, malignant melanoma.[15] This form of skin cancer is rare, but it causes 75% of all skin cancer-related deaths. Increased risk of malignant melanoma in sunscreen users has been the subject of many epidemiological studies
Symptoms
Typically there is initial redness (erythema), followed by varying degrees of pain, proportional in severity to both the duration and intensity of exposure.
Other symptoms are edema, itching, peeling skin, rash, nausea, fever, and syncope. Also, a small amount of heat is given off from the burn, caused by the concentration of blood in the healing process, giving a warm feeling to the affected area. Sunburns may befirst- or second-degree burns.
One should immediately speak to a dermatologist if one develops a skin lesion that has an asymmetrical form, has darker edges than center, changes color, or becomes larger than 1/4 inch (6 mm). (see Melanoma)
Duration
Sunburn can occur in less than 15 minutes, and in seconds when exposed to non-shielded welding arcs or other sources of intense ultraviolet light. Nevertheless, the inflicted harm is often not immediately obvious.
After the exposure, skin may turn red in as little as 30 minutes but most often takes 2 to 6 hours. Pain is usually most extreme 6 to 48 hours after exposure. The burn continues to develop for 24 to 72 hours, occasionally followed by peeling skin in 3 to 8 days. Some peeling and itching may continue for several weeks.
Long-term low-intensity exposure to sunlight is known to cause significant ageing of the skin; other health effects are not accurately known. A particular example with very noticeable ageing is that of a 69-year-old truck driver in Chicago, USA who drove in the city for 28 years. A photograph of his face[27][28] shows a great deal of ageing on the left side, where he was exposed to sunlight all day, while the right side has the "taut, unblemished face of an apparently much younger man".[28][27] Window glass does not absorb UVA, which can penetrate the epidermis and upper layers of dermis. Chronic UVA exposure can cause photoageing: thickening of the epidermis and stratum corneum and destruction of elastic fibers; it can cause DNA mutations and toxicity which can lead to cancer, although less carcinogenic than UVB.
One of the most effective ways to prevent sunburn is to reduce the amount of UV radiation reaching the skin. The strength of sunlight is published in many locations as a UV index. The World Health Organization recommends to limit time in the midday sun (between 10 a.m. and 4 p.m.), to watch the UV index, to seek shade, to wear protective clothing and a wide-brim hat, and to use sunscreen.[29]Sunlight is generally strongest when the sun is close to the highest point in the sky. Due to time zones and daylight saving time, this is not necessarily at 12 p.m., but often one to two hours later.
Commercial preparations are available that block UV light, known as sunscreens or sunblocks. They have a sunburn protection factor (SPF) rating, based on the sunblock's ability to suppress sunburn: The higher the SPF rating the lower the amount of direct DNA damage.
A sunscreen rated as SPF 10 blocks 90% of the sunburn-causing UVB radiation; an SPF20-rated sunscreen blocks 95%[citation needed]. Modern sunscreens contain filters for UVA radiation as well as UVB. The stated protection factors are correct only if 2 μl of sunscreen is applied per square cm of exposed skin. This translates into about 28 ml (1 oz) to cover the whole body of an adult male, which is much more than many people use in practice. Although UVA radiation does not cause sunburn, it does contribute to skin aging and an increased risk of skin cancer. Many sunscreens provide broad-spectrum protection, meaning that they protect against both UVA and UVB radiation.
Research has shown that the best protection is achieved by application 15 to 30 minutes before exposure, followed by one reapplication 15 to 30 minutes after exposure begins. Further reapplication is necessary only after activities such as swimming, sweating, and rubbing.[30] This varies based on the indications and protection shown on the label — from as little as 80 minutes in water to a few hours, depending on the product selected.
When one is exposed to any artificial source of occupational UV, special protective clothing (for example, welding helmets/shields) should be worn.
There is also evidence that common foods may have some protective ability against sunburn if taken for a period before the exposure.[31] Beta-carotene and lycopene, chemicals found in tomatoes and other fruit, have been found to increase the skin's ability to resist the effects of UV light. In a 2007 study, after about 10–12 weeks of eating tomato-derived products, a decrease in sensitivity toward UV was observed in volunteers. Ketchup and tomato puree are both high in lycopene.[32] Dark chocolate rich inflavonoids has also been found to have a similar effect if eaten for long periods before exposure.
Eyes
The eyes are also sensitive to sun exposure. Wrap-around sunglasses or the use by spectacle-wearers of glasses that block UV light reduce harmful UV radiation. UV light has been implicated in the development of age-related macular degeneration[33], pterygium[34] and cataract.[35] Concentrated clusters of melanin, commonly known asfreckles, are often found within the iris.
[edit]Diet
Dietary factors influence susceptibility to sunburn, recovery from sunburn, and risk of secondary complications from sunburn. Several dietary antioxidants, including essential vitamins, have been shown to have some effectiveness for protecting against sunburn and skin damage associated with ultraviolet radiation, both in human and animal studies. Supplementation with Vitamin C and Vitamin E was shown in one study to reduce the amount of sunburn after a controlled amount of UV exposure.[36] A review of scientific literature through 2007 found that beta carotene (Vitamin A) supplementation had a protective effect against sunburn, but that the effects were only evident in the long-term, with studies of supplementation for periods less than 10 weeks in duration failing to show any effects.[37] Lutein, a carotenoid, was also found in a study on mice to protect against ultraviolet-induced inflammation and immunosuppression.[38]
Sunburn increases the metabolic demands on the body, increasing the needs for water and other nutrients to prevent skin breakdown and secondary infections.[39]
[edit]Treatment
The most important aspects of sunburn care are to avoid exposure to the sun while healing and to take precautions to prevent future burns. The best treatment for most sunburns is time. Most sunburns heal completely within a few weeks. Home treatments that help manage the discomfort or facilitate the healing process include using cool and wet cloths on the sunburned areas, taking frequent cold showers or baths, and applying soothing lotions that contain aloe vera[dubious ] to the sunburn areas. Topical steroids (such as 1% hydrocortisone cream) may also help with sunburn pain and swelling. The peeling that comes after some sunburn is inevitable. However, there are lotions that may relieve the itching. Acetaminophen (such as Tylenol), Nonsteroidal anti-inflammatory drugs (such as Ibuprofen or Naproxen), and Aspirin have all shown to reduce the pain of sunburns.[40]
Sunburn
General Considerations
Most sunburns are first-degree (erythema) or superficial partial-thickness (blisters) burns. Skin changes from sunburn are maximal about 12–24 hours after exposure. Patients usually present to the emergency department for pain relief. Occasionally a patient with extensive superficial partial-thickness burns will require fluid resuscitation and parenteral analgesics for pain control.
Clinical Findings
Diagnosis is based on a history of exposure to the sun (or to ultraviolet light in tanning beds) and physical findings of erythema and blistering.
Treatment
Sunburn can be difficult to treat. Saline-soaked dressings or calamine lotion may provide some relief from pain and itching. Ibuprofen and other nonsteroidal anti-inflammatory agents work by blocking the production of prostaglandins that are thought to be important mediators of pain in sunburned skin. Oral and topical corticosteroids have not been shown to significantly improve symptoms or decrease healing time. Patients with extensive partial-thickness sunburn should receive treatment according to the guidelines described for other thermal burns.
Disposition
Almost all patients with sunburn may receive treatment on an outpatient basis. If there are large blisters, the patient should be seen again in 2–3 days to make sure that secondary infection has not developed. Patients should be advised to avoid prolonged ultraviolet light exposure to the sun in the future and to use a sunscreen (eg, over-the-counter preparations containing PABA [p-aminobenzoic acid] or dioxybenzone) before exposure. Patients requiring fluid resuscitation or parenteral analgesics should be hospitalized.
Electrical Burns
See Chapter 46.
Ocular Burns
See also Chapter 31.
Essentials of Diagnosis
- High level of suspicion in patients with facial burns
- Evaluate for foreign bodies
- Examine eyes with fluorescein
General Considerations
Patients with thermal facial burns may also have burns to the eyelid and the eye itself. Chemical burns constitute one of the most common work-related injuries seen in U.S. emergency departments. Both types of burns may be associated with the development of massive periorbital edema that makes delayed examination difficult. Injury of the cornea or anterior chamber may occur and lead to permanent vision loss. It is therefore important that patients with suspected ocular burns be examined promptly, preferably in the emergency department.
Clinical Findings
Instill tetracaine, 0.5%, or proparacaine, 0.5%, in the conjunctival sac to decrease pain during examination. Systemic analgesia should also be provided when needed. Retract and evert the eyelids to look for foreign bodies. Remove particulates and contact lenses to prevent injury to the cornea due to pressure from edematous lids. Assess visual acuity. Corneal abrasions and thermal injury may be detected by instillingfluorescein in the conjunctival sac and examining the eye using the blue light on an ophthalmoscope or, if the patient's condition permits, a slit lamp. Most ocular burns cause uveitis, and cell and flare in the anterior chamber are apparent. Cycloplegics are indicated to prevent synechiae. Phenylephrine is contraindicated.
Treatment
Irrigate any suspected chemical burn of the eye with large amounts (at least 2 L) of sterile normal saline using a Morgan lens. Tap water and Ringers Lactate are sufficient alternatives. Restoration of physiologic pH is paramount, and irrigation should continue to this end. Treat corneal abrasions and thermal injuries by instilling an ophthalmic antibiotic in the conjunctival sac. Alkali burns cause liquefaction necrosis rapidly, may require larger amounts of irrigating fluid, and require emergency ophthalmologic consultation. 1% calcium gluconate drops should be considered for hydrofluoric acid exposure, but only used after discussion with an ophthalmologist.
Disposition
Burns of the eyes are major injuries. Obtain urgent ophthalmologic consultation.
Circumferential Burns of Neck, Chest, and Extremities
General Considerations
Circumferential deep burns of the neck may cause lymphatic and venous obstruction leading to laryngeal edema and airway obstruction. Circumferential chest wall injuries may impede chest wall movement and lead to respiratory failure. Circumferential burns of the extremities may restrict blood flow, causing increased tissue pressure with resultant ischemia. Scarring can also restrict range of motion and affect fine motor function.
Clinical Findings
Patients with deep circumferential neck wounds should undergo direct visualization of the larynx by laryngoscopy. Because laryngeal edema may develop hours after initial examination, frequent reevaluation may be necessary.
Monitor patients with circumferential chest wounds for signs of respiratory compromise (tachypnea, dyspnea, deteriorating arterial blood gas levels); measurement of forced vital capacity or peak airway pressure may be useful.
Carefully examine the extremity distal to the wound in patients with circumferential burns of the extremities. Look for evidence of ischemia (diminished pulses, poor capillary refill, anesthesia); loss of vibratory sense is an early sign. If available, a Doppler ultrasound device is useful to assess distal blood flow. Because edema continues to develop during the first 6–8 hours after burn injury of the extremities, frequent reevaluation is important.
Treatment
Patients with deep circumferential burns of the neck are candidates for early endotracheal intubation. Elevate the injured limb(s) of patients with circumferential wounds of the extremities in order to minimize development of edema. Remove rings or other jewelry that could act as a tourniquet when edema develops. If evidence of distal ischemia develops, escharotomy is indicated. Ideally this should be performed in a burn center by a surgeon experienced in this procedure. Occasionally escharotomy must be performed in the emergency department before the patient is transported to a burn center for definitive care. Sterilize the overlying skin and make medial and lateral incisions through the eschar using a No. 20 scalpel or electrocautery. Incise deeply enough to cut entirely through the burned skin and release the constricting eschar, being careful to avoid neurovascular structures (typically this occurs at the level of the subcutaneous fat). No anesthesia should be required as full-thickness burns are insensate. Blood loss is seldom significant but can be controlled by cautery or suture if necessary.
Patients with a circumferential chest wall burn may require escharotomy in the emergency department. Using sterile technique, incise the eschar along the anterior axillary line bilaterally to the costal margins, and then join these incisions with incisions along the costal margins and just below the clavicles. This releases a segment of chest wall eschar that can move with respiratory excursion.
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