<unk>  effect (as measured by the UV Index) is the product of the sunlight spectrum at the earth's surface (radiation intensity) and the erythemal action spectrum (skin sensitivity). Long-wavelength UV is more prevalent, but each milliwatt at 295 nm produces almost 100 times more<unk>  than at 315 nm. Skin peeling on the arm as a result of<unk>  – the destruction of lower layers of the epidermis causes rapid loss of the top layers Tanning of the forearm (visible darkening of the skin) after extended sun exposure The most effective way to prevent<unk>  is to reduce the amount of UV radiation reaching the skin. The World Health Organization, American Academy of Dermatology, and Skin Cancer Foundation recommend the following measures to prevent excessive UV exposure and skin cancer: * Limiting sun exposure between the hours of 10am and 4pm, when UV rays are the strongest * Seeking shade when UV rays are most intense * Wearing sun-protective clothing including a wide brim hat, sunglasses, and tightly-woven, loose-fitting clothing * Using sunscreen * Avoiding tanning beds and artificial UV exposure UV intensity The strength of sunlight is published in many locations as a UV Index. 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 noon, but often one to two hours later. Seeking shade including using umbrellas and canopies can reduce the amount of UV exposure, but does not block all UV rays. The WHO recommends following the shadow rule: "Watch your shadow – Short shadow, seek shade!" Sunscreen Commercial preparations are available that block UV light, known as sunscreens or sunblocks. They have a sun protection factor (SPF) rating, based on the sunblock's ability to suppress<unk> : The higher the SPF rating, the lower the amount of direct DNA damage. The stated protection factors are correct only if 2 mg 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. Sunscreens function as chemicals such as oxybenzone and dioxybenzone that absorb UV radiation (chemical sunscreens) or opaque materials such as zinc oxide or titanium oxide to physically block UV radiation (physical sunscreens). Chemical and mineral 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<unk> , it does contribute to skin aging and an increased risk of skin cancer. Sunscreen is effective and thus recommended for preventing melanoma and squamous cell carcinoma. There is little evidence that it is effective in preventing basal cell carcinoma. Typical use of sunscreen does not usually result in vitamin D deficiency, but extensive usage may. Recommendations Research has shown that 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 only after activities such as swimming, sweating, and rubbing. 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. 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 Eyes The eyes are also sensitive to sun exposure at about the same UV wavelengths as skin; snow blindness is essentially<unk>  of the cornea. Wrap-around sunglasses or the use by spectacle-wearers of glasses that block UV light reduce the harmful radiation. UV light has been implicated in the development of age-related macular degeneration, pterygium and cataract. Concentrated clusters of melanin, commonly known as freckles, are often found within the iris. The tender skin of the eyelids can also become<unk> ed, and can be especially irritating. Lips The lips can become chapped (cheilitis) by sun exposure. Sunscreen on the lips does not have a pleasant taste and might be removed by saliva. Some lip balms (ChapSticks) have SPF ratings and contain sunscreens. Feet 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, and swimwear or swimgear that covers the foot. Diet Dietary factors influence susceptibility to<unk> , recovery from<unk> , and risk of secondary complications from<unk> . Several dietary antioxidants, including essential vitamins, have been shown to have some effectiveness for protecting against<unk>  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<unk>  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<unk> , 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. There is also evidence that common foods may have some protective ability against<unk>  if taken for a period before the exposure. Protecting children 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<unk>  at any age and protective measures can ensure their future risk of skin cancer is reduced. * 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 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 as well as 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 10am-4pm and seek shade. Sun protective clothing with a 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. When one is exposed to any artificial source of occupational UV, special protective clothing (for example, welding helmets/shields) should be worn. 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.
Sunburn
Windburn
Grocer's itch
Gangrene
Swimmer's itch
Photokeratitis
Pachyderma
Melasma