“Sunblock” redirects here. For the electronic music group, see Sunblock (band). For the Ball Park Music song, see Sunscreen (song).
Not to be confused with indoor tanning lotion, the suntan lotion which intensifies sun exposure.Sunscreen
Sunscreen on back under normal and UV lightOther namesSun screen, sunblock, sunburn cream, sun cream, block out
Sunscreen, also known as sunblock or suntan lotion, is a photoprotective topical product for the skin that absorbs or reflects some of the sun’s ultraviolet (UV) radiation and thus helps protect against sunburn and most importantly prevent skin cancer. Sunscreens come as lotions, sprays, gels, foams (such as an expanded foam lotion or whipped lotion), sticks, powders and other topical products. Sunscreens are common supplements to clothing, particularly sunglasses, sunhats and special sun protective clothing, and other forms of photoprotection (e.g. umbrellas, etc.).
The first sunscreen in the world was invented in Australia, by chemist H.A. Milton Blake, in 1932[dua] formulating with the UV filter ‘salol (Phenyl salicylate)’ at a concentration of ‘10%'[tiga] Its protection was verified by the University of Adelaide and it was also produced commercially by Blake’s company, Hamilton Laboratories.[lima] Despite sunscreen being relatively new, sun protection practices have been observed since at least the ancient Egyptians “who used ingredients such as rice bran, jasmine, and lupine” to provide sun protection.
Often, sunscreens are classified into inorganic (mistakenly called ‘physical’) sunscreens (i.e., zinc oxide and titanium dioxide) and organic (also, mistakenly referred to as ‘chemical’) sunscreens.
Despite popular belief, both types of sunscreens work mainly by absorption of UV light. Newer studies have found that inorganic sunscreens may absorb up to 95% of UV light, while its deflecting ability might be up to only lima% (less than SPF dua).
Medical organizations such as the American Cancer Society recommend the use of sunscreen because it aids in the prevention of squamous cell carcinomas. The routine use of sunscreens may also reduce the risk of melanoma. However, many sunscreens do not block Ultraviolet A (UVA) radiation, yet protection from UVA is important for the prevention of skin cancer.
To provide a better indication of their ability to protect against skin cancer and other diseases associated with UVA radiation (such as phytophotodermatitis), the use of broad-spectrum (UVA/UVB) sunscreens has been recommended.
In the United States, sunscreens are required to remain effective at original strength for at least three years. Some sunscreens include an expiration date—a date indicating when they may become less effective.
Diligent use of sunscreen can also help to slow or temporarily prevent the development of wrinkles, dark spots and sagging skin.Health effectsBenefits
Sunscreen use can help prevent melanoma and squamous cell carcinoma, two types of skin cancer. There is little evidence that it is effective in preventing basal cell carcinoma.
A 2013 study concluded that the diligent, everyday application of sunscreen could slow or temporarily prevent the development of wrinkles and sagging skin. The study involved 900 white people in Australia and required some of them to apply a broad-spectrum sunscreen every day for four and a half years. It found that people who did so had noticeably more resilient and smoother skin than those assigned to continue their usual practices. A study on 32 subjects showed that daily use of sunscreen (SPF 30) reversed photoaging of the skin within 12 weeks and the amelioration continued until the end of the investigation period of one year.
A tube of SPF 30 sunblock on sale in the United States.
Minimizing UV damage is especially important for children and fair-skinned individuals and those who have sun sensitivity for medical reasons.Potential risks
In 2009, the Therapeutic Goods Administration of Australia updated a review of sunscreen paling aman studies and concluded: “The potential for titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles in sunscreens to cause adverse effects depend primarily upon the ability of the nanoparticles to reach viable skin cells. To date, the current weight of evidence suggests that TiO2 and ZnO nanoparticles do not reach viable skin cells.” Sunscreen ingredients typically undergo extensive review by government regulators in multiple countries, and ingredients that present significant safety concerns (such as PABA) tend to be withdrawn from the consumer market.
There is a risk of an allergic reaction to sunscreen for some individuals, as “Typical allergic contact dermatitis may occur in individuals allergic to any of the ingredients that are found in sunscreen products or cosmetic preparations that have a sunscreen component. The rash can occur anywhere on the body where the substance has been applied and sometimes may spread to unexpected sites.”Vitamin D production
There are some concerns about potential vitamin D deficiency arising from prolonged use of sunscreen. The typical use of sunscreen does not usually result in vitamin D deficiency; however, extensive usage may. Sunscreen prevents ultraviolet light from reaching the skin, and even moderate protection can substantially reduce vitamin D synthesis. However, adequate amounts of vitamin D can be produced with moderate sun exposure to the face, arms and legs, averaging 5–30 minutes twice per week without sunscreen. (The darker the complexion, or the weaker the sunlight, the more minutes of exposure are needed, approximating 25% of the time for minimal sunburn.) Vitamin D overdose is impossible from UV exposure due to an equilibrium the skin reaches in which vitamin D degrades as quickly as it is created.
Studies showed that sunscreen with a high UVA protection factor enabled significantly higher vitamin D synthesis than a low UVA protection factor sunscreen, likely because it allows more UVB transmission.Measurements of protection
Sunscreen helps prevent sunburn, such as this, which has blistered.Sun protection factor and labeling 
Two photographs showing the effect of applying sunscreens in visible light and in UVA. The photograph on the right was taken using ultraviolet photography shortly after application of sunscreen to half of the face.
The sun protection factor (SPF rating, introduced in 1974) is a measure of the fraction of sunburn-producing UV rays that reach the skin. For example, “SPF 15” means that 1⁄15 of the burning radiation will reach the skin, assuming sunscreen is applied evenly at a thick dosage of 2 milligrams per square centimeter (mg/cm2). It is important to note that sunscreens with higher SPF do not last or remain effective on the skin any longer than lower SPF and must be continually reapplied as directed, usually every two hours.
The SPF is an imperfect measure of skin damage because invisible damage and skin aging are also caused by ultraviolet type A (UVA, wavelengths 315–400 or 320–400 nm), which does not primarily cause reddening or pain. Conventional sunscreen blocks very little UVA radiation relative to the nominal SPF; broad-spectrum sunscreens are designed to protect against both UVB and UVA. According to a 2004 study, UVA also causes DNA damage to cells deep within the skin, increasing the risk of malignant melanomas. Even some products labeled “broad-spectrum UVA/UVB protection” have not always provided good protection against UVA rays. Titanium dioxide probably gives good protection, but does not completely cover the UVA spectrum, as early 2000s research suggests that zinc oxide is superior to titanium dioxide at wavelengths 340–380 nm.
Owing to consumer confusion over the real degree and duration of protection offered, labeling restrictions are enforced in several countries. In the EU, sunscreen labels can only go up to SPF 50+ (initially listed as 30 but soon revised to 50). Australia’s Therapeutic Goods Administration increased the upper limit to 50+ in 2012. In its 2007 and 2011 draft rules, the US Food and Drug Administration (FDA) proposed a maximum SPF label of 50, to limit unrealistic claims. (As of February 2017, the FDA has not adopted the SPF 50 limit.) Others have proposed restricting the active ingredients to an SPF of no more than 50, due to lack of evidence that higher dosages provide more meaningful protection. Different sunscreen ingredients have different effectiveness against UVA and UVB.
UV sunlight spectrum (on a summer day in the Netherlands), along with the CIE Erythemal action spectrum. The effective spectrum is the product of the former two.