Sunscreen: Difference between revisions

Sunscreen
Sunscreen on back under normal and UV light
Other names	Sun screen, sunblock, suntan lotion, sunburn cream, sun cream, block out[1]
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Sunscreen, also known as sunblock and suntan lotion, is a

Benefits

Sunscreen use can help prevent

A 2013 study concluded that the diligent, everyday application of sunscreen can slow or temporarily prevent the development of wrinkles and sagging skin.[9] 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.^[9]

Minimizing UV damage is especially important for children and fair-skinned individuals and those who have sun sensitivity for medical reasons.^[10]

Potential risks

In 2009, the

Concerns have also been raised about potential vitamin D deficiency arising from prolonged use of sunscreen. Typical use of sunscreen does not usually result in vitamin D deficiency; however, extensive usage may.^[13] Sunscreen prevents ultraviolet light from reaching the skin, and even moderate protection can substantially reduce vitamin D synthesis.^[14][15] 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 thanks to an equilibrium the skin reaches in which vitamin D degrades as fast as it is created.^[16][17][18]

Measurements of protection

Sun protection factor and labeling

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 1/15th 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). A user can determine the effectiveness of a sunscreen "by multiplying the SPF factor by the length of time it takes for him or her to suffer a burn without sunscreen."^[19] Thus, if a person develops a sunburn in 10 minutes when not wearing a sunscreen, the same person in the same intensity of sunlight will avoid sunburn for 150 minutes if wearing a sunscreen with an SPF of 15.^[19] 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.^[20]

The SPF is an imperfect measure of skin damage because invisible damage and skin aging are also caused by

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).^[27] Australia's Therapeutic Goods Administration increased the upper limit to 50+ in 2012.^[28][29] 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.^[30][31][32] (As of February 2017, the FDA has not adopted the SPF 50 limit.^[33]) 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.^[34] Different sunscreen ingredients have different effectiveness against UVA and UVB.^[35]

The SPF can be measured by applying sunscreen to the skin of a volunteer and measuring how long it takes before sunburn occurs when exposed to an artificial sunlight source. In the US, such an in vivo test is required by the FDA. It can also be measured in vitro with the help of a specially designed spectrometer. In this case, the actual transmittance of the sunscreen is measured, along with the degradation of the product due to being exposed to sunlight. In this case, the transmittance of the sunscreen must be measured over all wavelengths in sunlight's UVB–UVA range (290–400 nm), along with a table of how effective various wavelengths are in causing sunburn (the erythemal action spectrum) and the standard intensity spectrum of sunlight (see the figure). Such in vitro measurements agree very well with in vivo measurements ^{[attribution needed]}.

Numerous methods have been devised for evaluation of UVA and UVB protection. The most-reliable spectrophotochemical methods eliminate the subjective nature of grading erythema.^[36]

The ultraviolet protection factor (UPF) is a similar scale developed for rating fabrics for sun protective clothing. According to recent testing by Consumer Reports, UPF ~30 is typical for protective fabrics, while UPF ~6 is typical for standard summer fabrics.^[37]

Mathematically, the SPF (or the UPF) is calculated from measured data as

${\displaystyle \mathrm {SPF} ={\frac {\int A(\lambda )E(\lambda )d\lambda }{\int A(\lambda )E(\lambda )/\mathrm {MPF} (\lambda )\,d\lambda }},}$

where ${\displaystyle E(\lambda )}$ is the solar irradiance spectrum, ${\displaystyle A(\lambda )}$ the erythemal action spectrum, and ${\displaystyle \mathrm {MPF} (\lambda )}$ the monochromatic protection factor, all functions of the wavelength ${\displaystyle \lambda }$. The MPF is roughly the inverse of the transmittance at a given wavelength.

The above means that the SPF is not simply the inverse of the transmittance in the UVB region. If that were true, then applying two layers of SPF 5 sunscreen would always be equivalent to SPF 25 (5 times 5). The actual combined SPF may be lower than the square of the single-layer SPF.^[38]

UVA protection

Persistent pigment darkening

The persistent pigment darkening (PPD) method is a method of measuring UVA protection, similar to the SPF method of measuring sunburn protection. Originally developed in Japan, it is the preferred method used by manufacturers such as L'Oréal.

Instead of measuring erythema or reddening of the skin, the PPD method uses UVA radiation to cause a persistent darkening or tanning of the skin. Theoretically, a sunscreen with a PPD rating of 10 should allow a person 10 times as much UVA exposure as would be without protection. The PPD method is an in vivo test like SPF. In addition, Colipa has introduced a method that, it is claimed, can measure this in vitro and provide parity with the PPD method.^[39]

SPF equivalence

As part of revised guidelines for sunscreens in the EU, there is a requirement to provide the consumer with a minimum level of UVA protection in relation to the SPF. This should be a "UVA PF" of at least 1/3 of the SPF to carry the UVA seal.^[40]

A set of final US FDA rules effective from summer 2012 defines the phrase "broad spectrum" as providing UVA protection proportional to the UVB protection, using a standardized testing method.^[31]

Star rating system

In the UK and Ireland, the

In August 2007, the FDA put out for consultation the proposal that a version of this protocol be used to inform users of American product of the protection that it gives against UVA;[30] but this was not adopted, for fear it would be too confusing.^[34]

PA system

Asian brands, particularly Japanese ones, tend to use The Protection Grade of UVA (PA) system to measure the UVA protection that a sunscreen provides. The PA system is based on the PPD reaction and is now widely adopted on the labels of sunscreens. According to the Japan Cosmetic Industry Association, PA+ corresponds to a UVA protection factor between two and four, PA++ between four and eight, and PA+++ more than eight. This system was revised in 2013 to include PA++++ which corresponds to a PPD rating of sixteen or above.

Sunblock

Sunblock typically refers to opaque sunscreen that is effective at blocking both UVA and UVB rays and uses a heavy carrier oil to resist being washed off. Titanium dioxide and zinc oxide are two minerals that are used in sunblock.^[41]

The use of the word "sunblock" in the marketing of sunscreens is controversial. Since 2013, the FDA has banned such use because it can lead consumers to overestimate the effectiveness of products so labeled.^[31] Nonetheless, many consumers use the words sunblock and sunscreen synonymously.

For total protection against damage from the sun, the skin needs to be protected from UVA, UVB, and also IRA (infrared-A light).^[42] Roughly 35% of solar energy is IRA.^{[citation needed]}. However, note that there is continuing debate within the dermatology community over the impact of sun-sourced IRA: Some sources indicate that early morning IRA exposure may be protective against further sun exposure by increasing cell proliferation and initiating anti-inflammatory cascades; these effects are not observed for artificial sources of intense IRA.^[43]

Active ingredients

In addition to moisturizers and other inactive ingredients, sunscreens contain one or more of the following active ingredients, which are either chemical or mineral in nature:

• Organic chemical compounds that absorb ultraviolet light.
• Inorganic particulates that reflect, scatter, and absorb UV light (such as titanium dioxide, zinc oxide, or a combination of both).^[41]
• Organic particulates that mostly absorb UV light like organic chemical compounds, but contain multiple
  chromophores that reflect and scatter a fraction of light like inorganic particulates. An example is Tinosorb M
  . The mode of action is about 90% by absorption and 10% by scattering.

Zinc oxide was approved as a UV filter by the EU in 2016.[58]

Other ingredients approved within the EU^[59] and other parts of the world,^[60] that have not been included in the current FDA Monograph:

^* Time and Extent Application (TEA), Proposed Rule on FDA approval originally expected 2009, now expected 2015.

Many of the ingredients awaiting approval by the FDA were relatively new, and developed to absorb UVA.^[62] The 2014 Sunscreen Innovation Act was passed to accelerate the FDA approval process.^[63][64]

Application

The dose used in FDA sunscreen testing is 2 mg/cm² of exposed skin.^[44] If one assumes an "average" adult build of height 5 ft 4 in (163 cm) and weight 150 lb (68 kg) with a 32-inch (82-cm) waist, that adult wearing a bathing suit covering the groin area should apply approximately 30 g (or 30 ml, approximately 1 oz) evenly to the uncovered body area. This can be more easily thought of as a "golf ball" size amount of product per body, or at least six teaspoonfuls. Larger or smaller individuals should scale these quantities accordingly.^[65] Considering only the face, this translates to about 1/4 to 1/3 of a teaspoon for the average adult face.

Some studies have shown that people commonly apply only 1/4 to 1/2 of the amount recommended for achieving the rated sun protection factor (SPF), and in consequence the effective SPF should be downgraded to a square root or 4th root of the advertised value.^[38] A later study found a significant exponential relation between SPF and the amount of sunscreen applied, and the results are closer to linearity than expected by theory.^[66]

Regulation

This section needs expansion. You can help by adding to it. (January 2018)

United States

Sunscreen labeling standards have been evolving in the United States since the FDA first adopted the SPF calculation in 1978.^[67] The FDA issued a comprehensive set of rules in June 2011, taking effect in 2012–2013, designed to help consumers identify and select suitable sunscreen products offering protection from sunburn, early skin aging, and skin cancer:^[31][68][69]

• To be classified as "broad spectrum", sunscreen products must provide protection against both
  UVB
  , with specific tests required for both.
• Claims of products being "
  waterproof
  " or "sweatproof" are prohibited, while "sunblock" and "instant protection" and "protection for more than 2 hours" are all prohibited without specific FDA approval.
• "Water resistance" claims on the front label must indicate how long the sunscreen remains effective and specify whether this applies to swimming or sweating, based on standard testing.
• Sunscreens must include standardized "Drug Facts" information on the container. However, there is no regulation that deems it necessary to mention whether the contents contain
  nanoparticles of mineral ingredients. (The EU has stricter regulation against the use of nanoparticles, and in 2009 introduced labeling requirements for nanoparticle ingredients in certain sunscreens and cosmetics.)^[70]

Certain sunscreens in water under ultraviolet light can increase the production of hydrogen peroxide, which damages phytoplankton.^[71] Oxybenzone damages coral.^[72] Nanoparticles of titanium dioxide, an ingredient in some sunscreens, can accumulate in coastal waters and be ingested by marine animals.^[71]

History

Early civilizations used a variety of plant products to help protect the skin from sun damage. For example, ancient Greeks used olive oil for this purpose, and ancient Egyptians used extracts of rice, jasmine, and lupine plants whose products are still used in skin care today.^[73] Zinc oxide paste has also been popular for skin protection for thousands of years.^[74]

Early synthetic sunscreens were first used in 1928.

Water-resistant sunscreens were introduced in 1977,[75] and recent development efforts have focused on overcoming later concerns by making sunscreen protection both longer-lasting and broader-spectrum, as well as more appealing to use.^[12]

Research

New products are in development such as sunscreens based on bioadhesive nanoparticles. These function by encapsulating commercially used UV filters, while being not only adherent to the skin but also non-penetrant. This strategy inhibits primary UV-induced damage as well as secondary free radicals.^[82]

Notes