For suntan lotion that intensifies sun exposure, see Indoor tanning lotion. For the electronic music group,

see Sunblock (band). For the song, see Wear Sunscreen.

Sunscreen (also commonly known as sunblock, sun tan lotion, sun screen, sun cream or block out) [1] is

a lotion, spray, gel or other topical product that absorbs or reflects some of the sun'sultraviolet (UV)

radiation on the skin exposed to sunlight and thus helps protect against sunburn. Skin-lightening

products have sunscreen to protect lightened skin because light skin is more susceptible to sun damage

than darker skin. A number of sunscreens have tanning powder to help the skin to darken or tan, however

tanning powder does not provide protection from UV rays.

Sunscreens contain one or more of the following ingredients:

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).

Organic particulates that mostly absorb light like organic chemical compounds, but contain

multiple chromophores, may reflect and scatter a fraction of light like inorganic particulates, and

behave differently in formulations than organic chemical compounds. An example is Tinosorb M.

Since the UV-attenuating efficacy depends strongly on particle size, the material is micronised to

particle sizes below 200 nm. The mode of action of this photostable filter system is governed to about

90% by absorption and 10% by scattering of UV light.

Depending on the mode of action sunscreens can be classified into physical sunscreens (i.e., those that

reflect the sunlight) or chemical sunscreens (i.e., those that absorb the UV light).[2]

Medical organizations such as the American Cancer Society recommend the use of sunscreen because it

prevents the squamous cell carcinoma and the basal cell carcinoma.[3] However, the use of sunscreens is

controversial for various reasons. Many sunscreens do not block UVA radiation, which does not cause

sunburn but can increase the rate of melanoma, another kind of skin cancer, andphotodermatitis, so

people using sunscreens may be exposed to high UVA levels without realizing it.[citation needed] The use of

broad-spectrum (UVA/UVB) sunscreens can address this concern.

The first effective sunscreen may have been developed by chemist Franz Greiter in 1938. The product,

called Gletscher Crème (Glacier Cream), subsequently became the basis for the company Piz

Buin (named in honor of the place Greiter allegedly obtained the sunburn that inspired his concoction),

which is still today a marketer of sunscreen products.[4] It has been estimated that Gletscher Crème had a

sun protection factor of 2.

The first widely used sunscreen was produced by Benjamin Green, an airman and later a pharmacist, in

1944. The product, Red Vet Pet (for red veterinary petrolatum), had limited effectiveness, working as a

physical blocker of ultraviolet radiation. It was a disagreeable red, sticky substance similar to petroleum

jelly. This product was developed during the height of World War II, when it was likely that the hazards of

sun overexposure were becoming apparent to soldiers in the Pacific and to their families at home. Sales

of this product boomed when Coppertone acquired the patent and marketed the substance under

the Coppertone girl and Bain de Soleil branding in the early 1950s.

Franz Greiter is credited with introducing the concept of sun protection factor (SPF) in 1962, which has

become a worldwide standard for measuring the effectiveness of sunscreen when applied at an even rate

of 2 milligrams per square centimeter (mg/cm2). Some controversy exists over the usefulness of SPF

measurements, especially whether the 2 mg/cm2 application rate is an accurate reflection of people’s

actual use.

Newer sunscreens have been developed with the ability to better withstand contact

with water, heat and sweat.

[edit]Measurements of sunscreen protection

Sunscreen helps prevent sunburn, such as this, which has blistered

[edit]Sun protection factor (SPF) and labeling requirements

Two photographs showing the effect of applying sunscreen 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 of a sunscreen is a laboratory measure of the effectiveness of sunscreen — the

higher the SPF, the more protection a sunscreen offers against UV-B (the ultraviolet radiation that

causes sunburn).[2]

The SPF is the amount of UV radiation required to cause sunburn on skin with the sunscreen on, as a

multiple of the amount required without the sunscreen.[5] There is a popular oversimplification of how SPF

determines how long one can stay in the sun. For example, many users believe that, if they normally get

sunburn in one hour, then an SPF 15 sunscreen allows them to stay in the sun fifteen hours (i.e. fifteen

times longer) without getting sunburn. This would be true if the intensity of UV radiation were the same for

the whole fifteen hours as in the one hour, but this is not normally the case. Intensity of solar radiation

varies considerably with time of day. During early morning and late afternoon, the sun's radiation intensity

is diminished since it must pass through more of the Earth's atmosphere while it is near the horizon.

In practice, the protection from a particular sunscreen depends, besides on SPF, on factors such as:

The skin type of the user.

The amount applied and frequency of re-application.

Activities in which one engages (for example, swimming leads to a loss of sunscreen from the skin).

Amount of sunscreen the skin has absorbed.

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

caused by ultraviolet type A (UVA, wavelength 320 to 400 nm), which does not 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.[6][7][8] According to a 2004 study, UVA also

causes DNA damage to cells deep within the skin, increasing the risk of malignant melanomas.[9] Even

some products labeled "broad-spectrum UVA/UVB protection" do not provide good protection against

UVA rays.[10] The best UVA protection is provided by products that contain zinc oxide, avobenzone,

and ecamsule. Titanium dioxide probably gives good protection, but does not completely cover the entire

UV-A spectrum, as recent research suggests that zinc oxide is superior to titanium dioxide at wavelengths

between 340 and 380 nm.[11]

Owing to consumer confusion over the real degree and duration of protection offered, labeling restrictions

are in force in several countries. In theEU sunscreen labels can only go up to SPF 50+ (actually indicating

a SPF of 60 or higher)[12] while Australia's upper limit is 30+.[13] In the 2007 and 2011 draft rules, the Food

and Drug Administration (FDA) proposed a maximum SPF label of 50, to limit unrealistic claims.[14][15]

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 (especially due to the logarithmic

nature of the scale).[16]

UV-B 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.

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 the UV-B range (290–320 nm), along with a table of

how effective various wavelengths are in causing sunburn (the erythemal action spectrum) and the actual

intensity spectrum of sunlight (see the figure). Such in vitro measurements agree very well with in

vivo measurements.[17] Numerous methods have been devised for evaluation of UVA and UVB protection.

The most reliable spectrophotochemical methods eliminate the subjective nature of grading erythema.[18]

Mathematically, the SPF is calculated from measured data as

where   is the solar irradiance spectrum,   the erythemal action spectrum,

and   the monochromatic protection factor, all functions of the wavelength  . 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 UV-B region. If

that were true, then applying two layers of SPF 5 sunscreen would be equivalent to SPF 25 (5 times

5). The actual combined SPF is always lower than the square of the single-layer SPF.

[edit]Measurements of UVA protection

[edit]Persistent pigment darkening (PPD)

The persistent pigment darkening (PPD) method is a method of measuring UVA protection, similar to

the SPF method of measuring UVB light 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.[19]

[edit]SPF equivalence

The UVA seal used in the EU

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. The implementation of this seal is in its phase-in period,[when?] so a sunscreen without it may already offer this protection.[20]

A set of final U.S. FDA rules going into effect for summer 2012 defines the phrase "broad spectrum"

as having a UVA SPF at least as high as the UVB SPF.[15]

[edit]Star rating system

In the UK and Ireland, the Boots star rating system is a proprietary in vitro method used to describe

the ratio of UVA to UVB protection offered by sunscreen creams and sprays. Based on original work

by Prof. Brian Diffey at Newcastle University, the Boots Company in Nottingham, UK, developed a

standard method that has been adopted by most companies marketing these products in the UK.

The logo and methodology of the test are licenced for a token fee to any manufacturer or brand of

sunscreens that are sold in the Boots retail chain, provided the products to which the logo is applied

perform to the standard claimed. Own Label products exclusively sold in other retailers are now

excluded from the terms of the licence. It should not be confused with SPF, which is measured with

reference to burning and UVB. One-star products provide the least ratio of UVA protection; five-star

products are best. The method has recently been revised in the light of the Colipa UVA PF test, and

with the new EU recommendations regarding UVA PF. The method still uses aspectrophotometer to

measure absorption of UVA vs UVB; the difference stems from a requirement to pre-irradiate

samples (where this was not previously required) to give a better indication of UVA protection, and of

photostability when the product is used. With the current methodology, the lowest rating is three

stars, the highest being five stars. 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, [21] but after concern this would be too confusing this was not adopted.[16]

[edit]PA system

Asian brands, particularly Japanese ones, tend to use the PA system as a measure of UVA

protection. There are four levels of protection: PA. PA+, PA++ and PA+++. It is recommended that

one uses a sunblock with at least PA++ protection.

[edit]Sunblock is a type of sunscreen

A tube of SPF 15 sun block lotion

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 of the

important ingredients in sunblock. Unlike the organic sun-blocking agents used in many sunscreens,

these metal oxides do not degrade with exposure to sunlight.

The use of the word "sunblock" in the marketing of sunscreens is controversial. The FDA has

considered banning such use because it can lead consumers to overestimate the effectiveness of

products so labeled.[22]

For total protection against damage from the sun, the skin needs to be protected from UVA, UVB and

IRA (infrared light). Roughly 35% of solar energy is IRA.[23]

[edit]Potential health risks

Main article: Sunscreen controversy

This article has been nominated to be checked for its neutrality. Discussion of this

nomination can be found on the talk page. (January 2012)

This article needs attention from an expert on the subject. See the talk page for

details. WikiProject Medicine  or the Medicine Portal may be able to help recruit an

expert. (February 2012)

As a defense against UV radiation, the amount of the brown pigment melanin in the skin increases

when exposed to moderate (depending on skin type) levels of radiation; this is commonly known as

a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless

heat, blocking the UV from damaging skin tissue. UVA gives a quick tan that lasts for days by

oxidizing melanin that was already present and triggers the release of the melanin from melanocytes.

UVB on the other hand yields a tan that takes roughly two days to develop because it stimulates the

body to produce more melanin. The photochemical properties of melanin make it an

excellent photoprotectant.

Sunscreen chemicals on the other hand cannot dissipate the energy of the excited state as efficiently

as melanin and therefore the penetration of sunscreen ingredients into the lower layers of the skin

increases the amount of free radicals and reactive oxygen species (ROS).[24]

Some sunscreen lotions now include compounds such as titanium dioxide and zinc oxide, inert fillers

which helps protect against UV rays via light scattering and physically blocking the light pathway into

the dermal layers. Other UVA blocking compounds found in sunscreen include Avobenzone. There

are also naturally occurring compounds found in rainforest plants that have been known to protect the

skin from UV radiation damage, such as the fern Phlebodium aureum .

Some sunscreen chemicals produce potentially harmful substances if they are illuminated while in

contact with living cells.[25][26][27] The amount of sunscreen that penetrates through the stratum

corneum may or may not be large enough to cause damage. In one study of sunscreens, the authors

write:

The question whether UV filters acts on or in the skin has so far not been fully answered.

Despite the fact that an answer would be a key to improve formulations of sun protection

products, many publications carefully avoid addressing this question.[28]

In an experiment by Hanson et al. that was published in 2006, the amount of harmful reactive oxygen

species was measured in untreated and in sunscreen-treated skin. In the first 20 minutes the film of

sunscreen had a protective effect and the number of ROS species was smaller. After 60 minutes,

however, the amount of absorbed sunscreen was so high that the amount of ROS was higher in the

sunscreen-treated skin than in the untreated skin.[24]

George Zachariadis and E Sahanidou of the Laboratory of Analytical Chemistry, at Aristotle

University, in Thessaloniki, Greece, have now carried out an ICP-AES analysis of several

commercially available sunscreen creams and lotions. "The objective was the simultaneous

determination of titanium and several minor, trace or toxic elements (aluminum, zinc, magnesium,

iron, manganese, copper, chromium, lead, and bismuth) in the final products," the researchers say.

They concluded that "Most of the commercial preparations that were studied showed generally good

agreement to the ingredients listed on the product label." However, they also point out that the

quantitative composition of the products tested cannot be assessed because the product labels

usually do not provide a detailed break down of all ingredients and their concentrations. They also

point out that, worryingly, their tests consistently revealed the presence of elements not cited in the

product formulation, which emphasized the need for a standardized and official testing method for

multi-element quality control of these products.[29]

Some epidemiological studies indicate an increased risk of malignant melanoma for the sunscreen

user.[30][31][32][33][34][35][36][37] Despite these studies, no medical association has published

recommendations to not use sunblock. Different meta-analysis publications have concluded that the

evidence is not yet sufficient to claim a positive correlation between sunscreen use and malignant

melanoma.[38][39]

Adverse health effects may be associated with some synthetic compounds in sunscreens.[40] In 2007

two studies by the CDC highlighted concerns about the sunscreen chemical oxybenzone

(benzophenone-3). They first detected the chemicals in greater than 95% of 2000 Americans tested,

while the second found that mothers with high levels of oxybenzone in their bodies were more likely

to give birth to underweight baby girls.[41]

Concerns have been raised regarding the use of nanoparticles in sunscreen.[42] Theoretically,

sunscreen nanoparticles could increase rates of certain cancers, or diseases similar to those caused

by asbestos.[43] In 2006 the Therapeutic Goods Administration of Australia concluded a study and

found:

"There is evidence from isolated cell experiments that zinc oxide and titanium dioxide can induce free

radical formation in the presence of light and that this may damage these cells (photo-mutagenicity

with zinc oxide). However, this would only be of concern in people using sunscreens if the zinc oxide

and titanium dioxide penetrated into viable skin cells. The weight of current evidence is that they

remain on the surface of the skin and in the outer dead layer (stratum corneum) of the skin." [42]

[edit]Vitamin D

Artificial sunscreen absorbs ultraviolet light and prevents it from reaching the skin. It has been

reported that sunscreen with a sun protection factor (SPF) of 8 based on the UVB spectrum can

decrease vitamin D synthetic capacity by 95 percent, whereas sunscreen with an SPF of 15 can

reduce synthetic capacity by 98 percent (Matsuoka et al., 1987).[44] Natural sunscreen has been

proved to improve pigmentation from sun tanning.

This was leading to deficiency in Australia after a government campaign to increase sunscreen use.[45] Doctors recommend spending small amounts of time in the sun without sun protection to ensure

adequate production of vitamin D.[46] When the UV index is greater than 3 (which occurs daily within

the tropics and daily during the spring and summer seasons in temperate regions) adequate amounts

of vitamin D3 can be made in the skin after only ten to fifteen minutes of sun exposure at least two

times per week to the face, arms, hands, or back without sunscreen. With longer exposure to UVB

rays, an equilibrium is achieved in the skin, and the vitamin simply degrades as fast as it is

generated.[47]

[edit]Active ingredients

The principal ingredients in sunscreens are

usually aromatic molecules conjugated with carbonyl groups. This general structure allows the

molecule to absorb high-energy ultraviolet rays and release the energy as lower-energy rays, thereby

preventing the skin-damaging ultraviolet rays from reaching the skin. So, upon exposure to UV light,

most of the ingredients (with the notable exception ofavobenzone) do not undergo significant

chemical change, allowing these ingredients to retain the UV-absorbing potency without

significant photodegradation.[48] A chemical stabilizer is included in some sunscreens containing

avobenzone to slow its breakdown - examples include formulations containing Helioplex [49]  and

AvoTriplex.[50] The stability of avobenzone can also be improved bybemotrizinol,[51] octocrylene [52]  and

various other photostabilisers.

[edit]FDA allowable ingredients

The following are the FDA allowable active ingredients in sunscreens:

UV-filter Other namesMaximum

concentration

Permitted in

these

countries

Results of safety

testing

p-Aminobenzoic acid PABA

15% (EC-

banned from

sale to

consumers

from 8 October

2009)

USA, AUS

Protects against

skin tumors in mice.[53][54][55]Shown to

increase DNA

defects, however,

and is now less

commonly used.

Padimate OOD-PABA, octyldimethyl-

PABA, σ-PABA

8%

(EC,USA,AUS)

10% (JP)

(Not currently

supported in

EU and may

be delisted)

EC, USA,

AUS, JPNot tested

Phenylbenzimidazole

sulfonic acid

Ensulizole, Eusolex 232,

PBSA, Parsol HS

4% (US,AUS)

8% (EC) 3%

(JP)

EC,USA,

AUS, JP

Genotoxic in

bacteria[56]

Cinoxate2-Ethoxyethyl p-

methoxycinnamate

3% (US) 6%

(AUS)USA, AUS Not tested

Dioxybenzone Benzophenone-8 3% USA, AUS Not tested

Oxybenzone

Benzophenone-3,

Eusolex 4360, Escalol

567

6% (US) 10%

(AUS,EU) 5%

(JP)

EC, USA,

AUS, JPNot tested

HomosalateHomomethyl salicylate,

HMS

10% (EC, JP)

15% (US,AUS)

EC, USA,

AUS, JPNot tested

Menthyl anthranilate Meradimate 5% USA, AUS Not tested

Octocrylene

Eusolex OCR, 2-cyano-

3,3diphenyl acrylic acid,

2-ethylhexylester

10%EC,USA,

AUS, JPIncreases ROS[24]

Octyl

methoxycinnamate

Octinoxate, EMC, OMC,

Ethylmethoxycinnamate,

7.5% (US)

10%

EC,USA,

AUS, JP

Escalol 557, 2-

ethylhexyl-

paramethoxycinnamate,

Parsol MCX

(EC,AUS)20%

(JP)

Octyl salicylateOctisalate, 2-Ethylhexyl

salicylate, Escalol 587,

5%

(EC,USA,AUS)

10% (JP)

EC,USA,

AUS, JPNot tested

Sulisobenzone

2-Hydroxy-4-

Methoxybenzophenone-

5-sulfonic acid,

3-benzoyl-4-hydroxy-6-

methoxybenzenesulfonic

acid, Benzophenone-4,

Escalol 577

5% (EC) 10%

(US, AUS, JP)

EC,USA,

AUS, JP

Trolamine salicylateTriethanolamine

salicylate12% USA, AUS Not tested

Avobenzone

1-(4-methoxyphenyl)-3-

(4-tert-butyl

phenyl)propane-1,3-

dione, Butyl methoxy

dibenzoylmethane,

BMDBM, Parsol 1789,

Eusolex 9020

3% (US) 5%

(EC,AUS)10%

(JP)

EC, USA,

AUS, JPNot available[57]

Ecamsule

Mexoryl SX,

Terephthalylidene

Dicamphor Sulfonic Acid

10%

EC,AUS

(US:Approved

in certain

formulations

up to 3% via

New Drug

Application

(NDA) Route)

Protects against

skin tumors in

mice[58][59][60]

Titanium dioxide CI7789125% (No limit

Japan)

EC,USA,

AUS, JPNot tested

Zinc oxide 25% (US) 20%

(AUS)

(EC-25%

provided

particle size

>100 nm)

EC,USA,

AUS, JP

Protects against

skin tumors in

mice[58]

(Japan, No

Limit)

Other ingredients approved within the EU[61] and other parts of the world,[62] that have not been

included in the current FDA Monograph:

UV-filter Other namesMaximum

concentration

Permitted

in

4-Methylbenzylidene

camphor

Enzacamene, Parsol 5000, Eusolex 6300,

MBC4%* EC, AUS

Tinosorb MBisoctrizole, Methylene Bis-Benzotriazolyl

Tetramethylbutylphenol, MBBT10%* EC, AUS,

JP

Tinosorb SBis-ethylhexyloxyphenol methoxyphenol

triazine, Bemotrizinol, BEMT, anisotriazine

10% (EC, AUS)

3% (JP)*

EC, AUS,

JP

Neo Heliopan AP

Bisdisulizole Disodium, Disodium phenyl

dibenzimidazole tetrasulfonate,

bisimidazylate, DPDT

10% EC, AUS

Mexoryl XL Drometrizole Trisiloxane 15% EC, AUS

Benzophenone-9

Uvinul DS 49, CAS 3121-60-6, Sodium

Dihydroxy Dimethoxy

Disulfobenzophenone [63]

10% JP

Uvinul T 150 Octyl triazone, ethylhexyl triazone, EHT5% (EC, AUS)

3% (JP)* EC, AUS

Uvinul A PlusDiethylamino Hydroxybenzoyl Hexyl

Benzoate10% (EC,JP) EC , JP

Uvasorb HEBIscotrizinol, Diethylhexyl butamido triazone,

DBT

10% (EC) 5%

(JP) * EC, JP

Parsol SLXDimethico-diethylbenzalmalonate,

Polysilicone-1510%

EC, AUS,

JP

Isopentenyl-4-

methoxycinnamate

Isoamyl p-Methoxycinnamate, IMC, Neo

Heliopan E1000, Amiloxate10% * EC, AUS

Many of the ingredients not approved by the FDA are relatively new and developed to absorb UVA.[64]

* Time and Extent Application (TEA), Proposed Rule on FDA approval expected 2009

[edit]Application

This section contains instructions, advice, or how-to content. The purpose of Wikipedia

is to present facts, not to train. Please help improve this article either by rewriting the how-to

content or by moving it to Wikiversity or Wikibooks. (October 2009)

Protection of the skin through use of a beach umbrella

Excessive exposure to direct sunlight is potentially harmful. Excessive exposure can result

in sunburn if a person does not wear sun protective clothing or use suitable sunscreen. Products with

a higher SPF (Sun Protection Factor) level provide greater protection against ultraviolet radiation.

However, in 1998, the Annual Meeting of the American Association for the Advancement of

Science reported that some sunscreens advertising UVA and UVB protection do not provide

adequate safety from UVA radiation and could give sun tanners a false sense of protection. A

sunscreen should also be hypoallergenic and noncomedogenic so it does not cause a rash or clog

the pores, which can cause acne.

For those choosing to tan, some dermatologists recommend the following preventative measures:

Sunscreens should block both UVA and UVB rays. These are called broad-spectrum sunscreens,

which should also be hypoallergenic and noncomedogenic so they do not cause a rash or clog

the pores, which can cause acne.

Sunscreens need to be applied thickly enough to get the full SPF protection.

Sunscreens should be applied 15 to 30 minutes before exposure, followed by one reapplication

15 to 30 minutes after the sun exposure begins. Further reapplication is necessary only after

activities such as swimming, sweating, and rubbing.[65]

Sun rays are strongest between 10 am and 4 pm.[66] Sun rays are stronger at

higher elevations (mountains) and latitudes near the equator.

Wearing a hat with a brim and anti-UV sunglasses can provide almost 100% protection against

ultraviolet radiation's entering the eyes.

Reflective surfaces like snow and water can greatly increase the amount of UV radiation to which

the skin is exposed.

Recent evidence indicates that caffeine and caffeine sodium benzoate increase UVB-

induced apoptosis both in topical and oral applications. In mice, UVB-inducedhyperplasia was greatly

reduced with administration of these substances. Although studies in humans remain untested,

caffeine and caffeine sodium benzoate may be novel inhibitors of skin cancer.[67]

[edit]Dosage

The dose used in FDA sunscreen testing is 2.2 mg/cm² of exposed skin.[48] Provided one assumes an

"average" adult build of height 5 ft 4 in (163 cm) and weight 150 lb (68 kg) with a 32 in (82 cm) waist,

that adult wearing a bathing suit covering the groin area should apply 29 g (approximately 1 oz)

evenly to the uncovered body area. Considering only the face, this translates to about 1/4 to 1/3 of a

teaspoon for the average adult face. Larger individuals should scale these quantities accordingly.

Contrary to the common advice that sunscreen should be reapplied every 2–3 hours, some research

has shown that the best protection is achieved by application 15–30 minutes before exposure,

followed by one reapplication 15–30 minutes after the sun exposure begins. Further reapplication is

only necessary after activities such as swimming, sweating, or rubbing/wiping.[68]

More recent research at the University of California, Riverside, indicates that sunscreen must be

reapplied within 2 hours in order to remain effective. Not reapplying could even cause more cell

damage than not using sunscreen at all, due to the release of extra free radicals from those

sunscreen chemicals that were absorbed into the skin.[24] Some studies have shown that people

commonly apply only 1/2 to 1/4 of the amount recommended to achieve the rated sun protection

factor (SPF), and in consequence the effective SPF should be downgraded to a square or 4th root of

the advertised value.[69]A later study found a significant exponential relation between SPF and the

amount of sunscreen applied and the results are closer to the linearity than expected by theory. [70]

[edit]Label regulations

Updated package labeling standards in the United States have been under development since 1978.

A set of final FDA rules going into effect for summer 2012 bans "waterproof" claims instead requiring

claims of 40 or 80 minutes "water-resistant" protection. It also required a standardized "Drug Facts"

label and requires specific FDA approval for "sunblock" and "instant protection" labels. Claims of

protection over 2 hours are not allowed without specific approval.[