1.Definition of sunburn
Sunburn is a form of radiation burn that affects living tissue, such as skin, that results from an overexposure to ultraviolet (UV) radiation.
Common symptoms in humans include ：
(1) red or reddish skin (2) hot to the touch (3) painful (4) general fatigue (5) mild dizziness (6) blistering (7) peeling skin (8) swelling (9) itching
Sunburn is an inflammatory. response in the tissue triggered by direct DNA damage by UV radiation. When the cells' DNA is overly damaged by UV radiation, type I cell-death is triggered and the tissue is replaced. Excessive UV radiation is the leading cause of non-malignant skin tumors, which in extreme cases can be life-threatening.
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
There is initial redness, followed by varying degrees of pain and damage, proportional in severity to the duration and intensity of sun exposure.
Heat is produced from capillaries close to the skin surface, therefore the affected area feels hot to touch.
· Duration for sunburn
A Few Seconds —Sunburn occur while exposed to non-shielded welding arcs or other sources of intense ultraviolet light.
15 Minutes — Sunburn occur while exposed in response to sun, the inflicted harm is often not immediately obvious.
30 Minutes — The skin may turn red and can see the red spots.
2 To 6 Hours — Sunburn begins to occur with mild itching, pain, and inflammation of the skin.
· After sunburn
6 To 48 Hours — Pain is usually strongest, inflammation continues and the skin becomes red and darker.
1 To 3 Days — The burn continues to develop, blisters may occur and ulceration occurs in inflamed areas.
3 To 8 Days — Occasionally followed by peeling skin after inflammation subsides.
Several Weeks — Some peeling and itching may continue.
· Sunburn in different areas
The eyes are also sensitive to sun exposure at about the same UV wavelengths as skin; snow blindness is sunburn of the cornea. Wrap-around sunglasses or the use by spectacle-wearers of glasses that block UV light reduce harmful radiation. UV light has been implicated in the development of age-related macular degeneration, pterygium and cataracts.
The tender skin of the eyelids can also become sunburned and can be especially irritating.
The lips can become chapped (cheilitis) by sun exposure. Some lip balms (ChapSticks) have SPF ratings and contain sunscreens.
The skin of the feet is often tender and protected, so sudden prolonged exposure to UV radiation can be particularly painful and damaging to the top of the foot. Protective measures include sunscreen, socks, or swimwear that covers the foot.
· Skin cancer
Ultraviolet radiation causes sunburns and increases the risk of three types of skin cancer:
(2) basal-cell carcinoma
(3) squamous-cell carcinoma.
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 sunscreen product use.
· Differential diagnosis
(1) Phototoxic reactions: Non-immunological response to sunlight interacting with certain drugs and chemicals in the skin which resembles an exaggerated sunburn.
(2) Photoallergic reactions: Uncommon immunological response to sunlight interacting with certain drugs and chemicals in the skin. Photoallergic reactions can cause intense itching and can lead to thickening of the skin.
(3) Phytophotodermatitis: UV radiation induces skin inflammation after contact with certain plants (including limes, celery, and meadow grass). Causes pain, redness, and blistering of the skin in the distribution of plant exposure.
(4) Polymorphic light eruption: Recurrent abnormal reactions to UVR present in various ways, including pink-to-red bumps, blisters, plaques and urticaria.
(5) Solar urticaria: A rare allergic reaction to the sun that occurs within minutes of exposure and fades within hours.
(6) Other skin diseases exacerbated by sunlight: Several dermatologic conditions can increase in severity with exposure to UVR. These include systemic lupus erythematosus (SLE), dermatomyositis, acne, atopic dermatitis, and rosacea.
2.Cause — effects of the sun for skin
Sunburn is the body's reaction to direct DNA damage from UVB、 light.
This damage is mAainly the formation of a thymine dimer. The damage is recognized by the body, which then triggers several defense mechanisms:
· DNA repair to revert the damage
· Apoptosis and peeling to remove irreparably damaged skin cells
· Increased melanin production to prevent future damage.
Sunburn causes an inflammation process. These chemical compounds increase sensitivity to heat by reducing the threshold of heat receptor (TRPV1) activation from 109 °F (43 °C) to 85 °F (29 °C).
The pain may be caused by the overproduction of a protein called CXCL5, which activates nerve fibers.
Dark spot —
Suntans, which naturally develop in some individuals as a protective mechanism against the sun,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.
UVB rays are a primary mutagen that can only penetrate through the epidermal (outermost) layer of the skin, resulting in DNA mutations. These mutations arise due to chemical changes, the formation of cyclobutene pyrimidine dimers and photoproducts formed between adjacent pyrimidine bases. These mutations may be clinically related to specific signs of photoaging such as wrinkling, increasing in elastin and collagen damage
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.
* Medications：the risk of sunburn can be increased by pharmaceutical products that sensitize users to UV radiation. Certain antibiotics, oral contraceptives, antidepressants, acne medications, and tranquillizers have this effect.
The UV Index indicates the risk of sunburn at a given time and location. Contributing factors include:
(1) Time: In most locations, the sun's rays are strongest between approximately 10 am and 4 pm daylight saving time.
(2) Cloud cover：Even on an overcast day, a significant percentage of the sun's damaging UV radiation can pass through clouds.
(3) Reflective surfaces：Such as water, sand, concrete, snow, and ice. All of these reflect the sun's rays and can cause sunburns.
(4) Season：The sun's position in late spring and early summer can cause a more-severe sunburn.
(5) 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.
(6) Latitude： Between the polar and tropical regions, the closer to the equator, the more direct sunlight passes through the atmosphere over a year.
(7) Wavelengths： Longer wavelengths of UV radiation cause most sunburn because those wavelengths are more prevalent in ground-level sunlight.
(8) 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.
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.
The World Health Organization, American Academy of Dermatology, and Skin Cancer Foundation recommend the following measures to prevent excessive UV exposure and skin cancer:
(1) Using sunscreen — themost important method for prevent sunburn
(2) Limiting sun exposure between the hours of 10 am and 4 pm, when UV rays are the strongest
(3) Seeking shade when UV rays are most intense
(4) Wearing sun-protective clothing, including a wide-brim hat, sunglasses, and tightly woven, loose-fitting clothing
(5) Avoiding tanning beds and artificial UV exposure
Sunscreens have a sun 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. The highest SPF rating js SPF50+,can prevent more than 98% UVB from sunshine.
The stated protection factors are correct only if 2 mg of sunscreen is applied per square cm of exposed skin translates into about 28 mL (1 oz) to cover the whole body of an adult male.
Sunscreens function as chemicals such as oxybenzone and dioxybenzone (organic sunscreens) or opaque materials such as zinc oxide or titanium oxide (inorganic sunscreens) that mainly absorb UV radiation.
Different sunscreens vary in the wavelengths of UV radiation blocked.
Broad-spectrum sunscreens contain filters that protect against UVA radiation as well as UVB. Although UVA radiation does not primarily cause sunburn, it contributes to skin aging and increases skin cancer risk.
Sunscreen is effective and thus recommended for preventing melanoma and squamous cell carcinoma.Typical use of sunscreen does not usually result in vitamin D deficiency.
[ Usage ]
Chemical sunscreens：The best sunscreen 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 after activities such as swimming, sweating, and rubbing. Recommendations are product dependent varying from 80 minutes in water to hours based on the indications and protection shown on the label.
Mineral sunscreens：Mineral sunscreens will take effect immediately after application, there is no need to apply in advance, it provides a layer of rebound protection shield for the skin, will not be broken down by the sun, so do not need to reapply often, if swimming, surfing, you need to pay attention to the waterproof index of the Mineral sunscreens, to determine whether you need to reapply.
The American Academy of Dermatology recommends the following criteria in selecting a sunscreen:
· Broad spectrum: protects against both UVA and UVB rays
· SPF 30 or higher
· Water resistant: sunscreens are classified as water resistant based on time, either 40 minutes, 80 minutes, or not water resistant
TreatmentThe primary measure of treatment is avoiding further exposure to the sun. The best treatment for most sunburns is time; most sunburns heal completely within a few weeks.
The American Academy of Dermatology.recommends the following for the treatment of sunburn:· For pain relief, take cool baths or showers frequently.
· Use soothing moisturizers that contain aloe vera or soy.
· Anti-inflammatory medications such as ibuprofenor aspirin can help with pain.
· Keep hydrated and drink extra water.
· Do not pop blisterson a sunburn; let them heal on their own instead.
· Protect sunburned skin (see: Sun protective clothingand Sunscreen) with loose clothing when going outside to prevent further damage while not irritating the sunburn.
A home treatment that may help the discomfort is using cool and wet cloths on the sunburned areas. Furthermore, sunburn draws fluid to the skin's surface and away from the rest of the body. Drinking extra water is recommended to help prevent dehydration.
Dietary factors influence susceptibility to sunburn, recovery from sunburn, and risk of secondary complications. Several dietary antioxidants, including essential vitamins, are effective in protecting against sunburn and skin damage associated with ultraviolet radiation, in both 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. A review of scientific literature through 2007 found that beta carotene (Vitamin A) supplementation had a protective effect against sunburn. The effects of beta carotene were only evident in the long-term, with studies of supplementation for periods less than ten weeks in duration failing to show any effects. There is also evidence that common foods may have some protective ability against sunburn if taken for a period before exposure.
[Foods to help reduce sunburn]
Green tea, cucumber, strawberries, lemon, watermelon, tomatoes, pomegranate, dark chocolate
Babies and children are particularly susceptible to UV damage which increases their risk of both melanoma and non-melanoma skin cancers later in life. Children should not sunburn at any age, and protective measures can reduce their future risk of skin cancer.
Infants 0–6 months: Children under 6mo generally have skin too sensitive for sunscreen and protective measures should focus on avoiding excessive UV exposure by using window mesh covers, wide-brim hats, loose clothing that covers the skin, and reducing UV exposure between the hours of 10am and 4pm.
Infants 6–12 months: Sunscreen can safely be used on infants this age. It is recommended to apply a broad-spectrum, water-resistant SPF 30+ sunscreen to exposed areas and avoid excessive UV exposure by using wide-brim hats and protective clothing.
Toddlers and Preschool-aged children: Apply a broad-spectrum, water-resistant SPF 30+ sunscreen to exposed areas, use wide-brim hats and sunglasses, avoid peak UV intensity hours of 10 am - 4 pm and seek shade. Sun-protective clothing with an SPF rating can also provide additional protection.
Artificial UV exposure
The WHO recommends that artificial UV exposure, including tanning beds, should be avoided as no safe dose has been established. Special protective clothing (for example, welding helmets/shields) should be worn when exposed to any artificial source of occupational UV. Such sources can produce UVC, an extremely carcinogenic wavelength of UV, which ordinarily is not present in normal sunlight, having been filtered out by the atmosphere.