Sunscreen

Sunscreen (also known as sunblock, suntan lotion) is a lotion, spray or other topical product that is supposed to protect the skin from the sun's ultraviolet (UV) radiation. While sunscreen does reduce sunburn and other skin damage, the use of sunscreen causes an increased risk of melanoma. Epidemological studies have shown repeatedly that the sunscreen-user has a higher risk of skin cancer than the non-user. In Europe and Australia the sunscreen ingredients are not tested by the authorities for photocarcinogenic effects, , however, in the USA the newer formulations are tested for photocarcinogenic effects. The most common ingredients in sunscreens on the market today were introduced before this testing became compulsory.

In the United States, the term suntan lotion usually means the opposite of sunscreen, and instead refers to lotion designed to moisturize and maximize UV exposure and tanning rather than block it. These are commonly called indoor tanning lotions when designed for use with tanning beds and have no sunscreen in them, or just suntan lotion if designed for outdoor use which may or may not have sunscreen protection in them.

The most effective sunscreens protect against both UVB (ultraviolet radiation with wavelength between 280 and 320 nm), which can cause sunburn, and UVA (between 320 and 400 nm), which penetrates the skin more deeply, with overexposures resulting in more long-term effects, such as premature skin aging. Most sunscreens work by containing either an organic chemical compound that absorbs ultraviolet light (such as oxybenzone) or an opaque material that reflects light (such as titanium dioxide, zinc oxide), or a combination of both. Typically, absorptive materials are referred to as chemical blocks, whereas opaque materials are mineral or physical blocks.

Dosing

Dosing for sunscreen can be calculated using the formula for body surface area and subsequently subtracting the area covered by clothing that provides effective UV protection. The dose used in FDA sunscreen testing is 2 mg/cm2. 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.

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, and rubbing.

However, more recent research at the University of California, Riverside indicates that sunscreen needs to 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 absorbed chemicals. simon was rer 2008

Epidemiological connection between malignant melanoma and sunscreen use

All medical statistics, that have investigated the effect of sunscreen use, have found an increase of malignant melanoma cases associated with sunscreen use. Garland et al. have compared the population of Queensland with the rest of Australia, because in Queensland the use of sunscreen has been promoted the earliest and the strongest compared to the rest of Australia. The increased sunscreen consumption in Queensland has led to a steep rise in the number of melanoma cases. At the time of this study (1992) Queensland had the highest incidence number of melanoma cases in the world. In other parts of Australia the use of sunscreen had been promoted only later, and the melanoma rates increased in these other parts with the same a delay.

Hunter et al. have found a higher risk for skin cancer in women who used sunscreen than in those who did not use sunscreen This higher risk persisted even after multiple adjustments have been made for confounding factors like skin type and the amount of time spend outdoors.

Philippe Autier et al .have performed a case-control study with 418 melanoma cases and 438 healthy controls in France Belgium and Germany. They have investigated groups of people who had sunburns in their childhood and those who did not, they have investigated those who were aware of health hazards associated with exaggerated UV-exposure and those who were not aware. These corrections were made to account for convoluting factors like childhood sunburns which might trigger sunscreen use and increase skin cancer risks. They found higher risks for melanoma within each group for those individuals that use sunscreen. Thereby they excluded the convoluting factors, and it had been shown, that it is the sunscreen use itself that causes the skin cancer.

They stated that "due to the divorce between public health messages and results from epidemiological studies, prevention programmes should not affirm that sunscreen use prevents cutaneous melanoma."

Furthermore they underlined the importance of truthful information to the public: They found that the regular sunscreen user unaware of the dangers linked to exaggerated UV-exposure have a 12 times higher risk when compared to aware subjects who never use sunscreen.

Within the group of people unaware of the dangers linked to exaggerated UV-exposure the sunscreen users have a 3.36 times higher risk for melanoma than the non-user.

Westerdahl et al. have performed a case-control study on 571 patients with malignant melanoma and 913 healthy controls. All the patients and controls were asked about their history of sunburn, hair color, sunbathing habits (how long, how often) and - of course - use of sunscreen. They had found a significantly elevated risk for developing malignant melanoma associated with regular sunscreen use. Several adjustments were made with respect to the history of sunburns, hair color and other factors. They state that even in two groups that differ neither in sunbathing frequency nor in duration of each sunbathing session an increased risk for melanoma was found for those who always use sunscreen.

Sunburn and skin cancer

It is certainly true that a statistical correlation exists between the number of sunburns and the risk to develop skin cancer. This statistical correlation has in the past been interpreted as a causal connection. The medical community took this correlation as an indication that sunburns cause skin cancer. This has been shown to be wrong in several studies. Wolf and Kripke have shown that protecting against sunburn does not imply protection against other damaging effects of UV-radiation Genetic studies have investigated the mutations in the melanoma of skin cancer patients. The mechanism of DNA damage which produced the melanoma can be identified from the kind of mutation, and it was shown that malignant melanoma in healthy humans originate from direct DNA damage only in 8% of the cases and melanoma originate from the indirect DNA damage in 92 % of the cases . Since the direct DNA damage is connected to sunburn it can be said that sunburn causes only 8 % of the melanoma cases and the indirect DNA damage (which is often amplified by sunscreen because it penetrates into the skin) is responsible for 92 % of all melanoma cases.

(Indirect DNA damage is caused by reactive oxygen species (ROS), oxidative stress and free radicals)

Mechanisms of melanoma generation by the use of sunscreen

There are several contributers to the increased melanoma risk among sunscreen users:

• Since the medical community had send out the message that sunburn "causes" melanoma, many people feel safe as long as they slap their sunscreen on. In reality the cause of melanoma is the indirect DNA damage not the sunburn-causing direct DNA damage. One contributer to the harmful effects of sunscreen is the changed behaviour of the sunscreen user compared to the non-user. Sunscreen prevents any warning signal that the human skin usually generates when exposed to solar radiation. This absence of a warning signal gives a treacherous feeling of safety to the sunscreen-user. Since they are not afraid of a sunburn the sunscreen-users stay in the sun much longer and therefore they are exposed to a larger dose of radiation. This increases in turn the indirect DNA damage which is responsible for the development of almost all melanoma.
• UVB radiation stimulates the skin to generate more protective melanin. The UVB filters in sunscreen suppress this stimulus. Then the human body fails to recognise the danger and the skin does not produce this substance that would offer an efficient natural protection against UVB and UVA. Furthermore it can be speculated that the reduced tanning effect in the sunscreen user will cause him to spend more time in the sun thereby increasing the dose of harmful radiation.
• Another substantial contributer was the false assumption that little or none of the topically applied sunscreen would be absorbed into the skin. This has been proven wrong several times (see for example ).The medical community has treated sunscreen like an innert filter that does not get into contact with living tissue. Today it is well established that sunscreen does penetrate the epidermal barrier into the human skin in amounts which are large enough to cause serious damage due to an increase of photogenerated free radicals. Photocatalytic substances can damage biological tissue even at very small concentrations. While non-catalytic substances need to be fairly concentrated to do harm, a photocatalyst combined with UV-irradiation can be harmful even at concentrations as low as 10 μmol/l. This is due to the repeated reaction of such a catalyst - one photocatalyst molecule can produce millions of free radicals (and more). This catalytic property of the sunscreen chromophore seems to have eluded the medical doctors who did not understand the language of many warning photochemists.

At this time, sunscreen is not tested (in Europe, Japan and Australia) for photocarcinogenic effects before it is released onto the market. In the US such testing became compulsory in 1978, and since then only 3 new substances have managed to fullfill these new requirements - illustrating how difficult it is to create a sunscreen ingredient that is not photocarcinogenic. Even in the US most of the sunscreens that are sold had their ingredients permitted to the market before testing for photocarcinogenic effects became compulsory. Furthermore it is important to know that those tests for photocarcinogenic properties are comparing two test animals that stay in the sun for the same amount of time. And there are other restrictions of these tests aswell. For example the animal has not been naked for 100000 years - a time scale that is evolutionary relevant and humans have developed better defense mechanisms than those animals.

In summary the factors that lead to a higher melanoma risk in Sunscreen users are:

1. Changed behaviour of the sunscreen user due to a fake sense of safety
2. Skin penetration through the epidermal barrier and the ensuing photosensitization effect of sunscreen

animal tests

Experiments on mice have shown a protective effect of sunscreens against melanoma. The following experiments were performed in 1982, 1985 and 1990 - after this the animal protection policies do not allow animal testing for cosmetic products any more. In these experiments the mice were treated with sunscreen, and then immediately irradiated for only 10 minutes or for 3 to 7 minutes after this time the irradiation stopped and the next sunscreen + irradiation treatment was done after a 2 day break. Within these 10 minutes the sunscreen does not penetrate through the epidermal barrier. For this reason the mice were not affected by the photosensitaziation effect of the sunscreen chemicals as it is described in . Despite the obvious discrepancy between such an experimental design and a real situation of sunscreen use, these experiment have been widely used as arguments to promote the use of sunscreen. Obviously human use has a different time-pattern because most sunscreen users stay in the sun longer than 10 minutes. This longer time allows the sunscreen to diffuse into the skin which leads to free radical generation inside the skin.

photochemical properties of sunscreen ingredients vs. melanin

Melanin has an extremely efficient photoprotective mechanism that dissipates the energy from the UV-radiation as harmless heat. This property is crucial to avoid the indirect DNA damage. In this mechanism the excited state of the melanin gives of the energy into the vibrational modes of the molecule (heat) by a process that is called internal conversion. This way melanin does not act as a photosensitizer. This photochemical process has been optimized by nature for melanin out of necessity. The internal conversion of melanin is so fast, that more than 99.9 % of the energy is dissipated as heat.

Sunscreen ingredients do not posses this photoprotective property. They do not efficiently dissipate the absorbed energy. In fact many of those chemicals (e.g.: PABA, Benzophenone or Coumarin) are used as photosensitizers in chemical reactions. Coumarin is used as a dye in lasers. The property that makes it suitable for such an application is the long-lived excited state. Exactly this property is makes it unsuitable for use in sunscreen. It will act as a photosensitizer starting indirect DNA damage - all the while preventing sunburn. Chemicals with a long lived excited state - substances that are uses in chemistry as photosensitizers - should not be used in sunscreens. And yet they are.

History

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 today is a well-known marketer of sunscreen products. Some internet articles suggest that Gletscher Crème had a sun protection factor of 2, although a research citation is not readily available online.

The first widely used sunscreen was produced by Benjamin Greene, 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.

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 withstand contact with water and sweat.

Measurements of sunscreen protection

Sun protection factor

The SPF of a sunscreen is a laboratory measure of the effectiveness of sunscreen; the higher the SPF, the more protection a sunscreen offers against UVB (the ultraviolet radiation that causes sunburn). The SPF indicates the time a person can be exposed to sunlight before getting sunburn with a sunscreen applied relative to the time they can be exposed without sunscreen. For example, someone who would burn after 12 minutes in the sun would expect to burn after 2 hours (120 min) if protected by a sunscreen with SPF 10. In practice, the protection from a particular sunscreen depends 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 is also caused by the very common ultraviolet type A, which does not cause reddening or pain. Conventional sunscreen does not block UVA as effectively as it does UVB, and an SPF rating of 30+ may translate to significantly lower levels of UVA protection according to a 2003 study. 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" do not provide good protection against UVA rays. 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 UVA spectrum.

Due to consumer confusion over the real degree and duration of protection offered, labeling restrictions are in force in several countries. In the United States in 1999, the Food and Drug Administration (FDA) decided to institute the labelling of SPF 30+ for sunscreens offering more protection, and a similar restriction applies in Australia. This was done to discourage companies from making unrealistic claims about the level of protection offered (such as "all day protection"), and because an SPF over 30 does not provide significantly better protection. In the EU sunscreens are limited to SPF 50+, indicating an SPF of 60 or higher.

UVB 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 UVB range (290–350 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.

Mathematically, the SPF is calculated from measured data as

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

where $E(\lambda )$ is the solar irradiance spectrum, $A(\lambda )$ the erythemal action spectrum, and $\mathrm {MPF} (\lambda )$ the monochromatic protection factor, all functions of the wavelength $\lambda$. 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 be equivalent to SPF 25 (5 times 5). The actual combined SPF is always lower than the square of the single-layer SPF.

Measurements of UVA protection

Persistent Pigment Darkening (PPD), Immediate Pigment Darkening (IPD), Boots Star System, Japanese PA system

The Persistent Pigment Darkening (PPD) method is a method of measuring UVA protection, similar to the SPF method of measuring UVB light protection. Theoretically, a sunscreen with a PPD rating of 10 should allow you to endure 10 times as much UVA as you would without protection.

The PPD is used as part of guidelines for EU sunscreens to provide the consumer with a minimum of UVA protection in relation to the SPF. The PPD should be at least 1/3 of the SPF to carry the UVA seal. The implementation of this seal is in its phase-in period, so a sunscreen without may already offer this protection.

The Japanese PA system ranges from PA+ to PA+++, with the + sign indicating increased UVA protection. However, studies have found the PA system to be inadequate, since the maximum PA (PA+++) is equivalent to a minimum protection of PPD8.

Star rating system

In the UK and Ireland, a star rating system is used to describe the ratio of UVA to UVB protection offered by sun screen creams and sprays. Invented by Dr Diffey of the Boots Company in Nottingham UK, it has been adopted by most companies marketing these products in the UK. 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 the best.

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 of avobenzone) do not undergo significant chemical change, allowing these ingredients to retain the UV absorbing potency without significant photo-degradation.

The following are the FDA allowable active ingredients in sunscreens:

• p-Aminobenzoic acid (PABA) up to 15 %.
• Avobenzone up to 3%.
• Cinoxate up to 3%.
• Dioxybenzone up to 3%.
• Homosalate up to 15%.
• Methyl anthranilate up to 5%.
• Octocrylene up to 10%.
• Octyl methoxycinnamate (Octinoxate) up to 7.5%.
• Octyl salicylate (Octisalate) up to 5%.
• Oxybenzone up to 6%.
• Padimate O up to 8%.
• Phenylbenzimidazole sulfonic acid (Ensulizole) up to 4%.
• Sulisobenzone up to 10%.
• Titanium dioxide up to 25%.
• Trolamine salicylate up to 12 %.
• Zinc oxide up to 25%.

Recently FDA approved:

• Mexoryl® SX (USAN Ecamsule, INCI Terephthalylidene Dicamphor Sulfonic Acid) - UVA absorber used in combination with other ingredients for UVB

Others approved within the EU and other parts of the world include:

• 4-Methylbenzylidene camphor ((INCI), USAN Enzacamene)
• Tinosorb® M (USAN Bisoctrizole, INCI Methylene Bis-Benzotriazolyl Tetramethylbutylphenol)
• Tinosorb® S (USAN Bemotrizinol, INCI Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine)
• Mexoryl® XL (INCI Drometrizole Trisiloxane)
• Neo Heliopan® AP (USAN Bisdisulizole Disodium, INCI Disodium Phenyl Dibenzimidazole Tetrasulfonate)
• Uvinul® A Plus (INCI Diethylamino Hydroxybenzoyl Hexyl Benzoate)
• Uvinul® T 150 (USAN Octyl Triazone, INCI Ethylhexyl Triazone)
• Uvasorb® HEB (USAN Iscotrizinol, INCI Diethylhexyl Butamido Triazone)
• Parsol® SLX (INCI Polysilicone-15)
• Amiloxate ((USAN), INCI Isoamyl p-Methoxycinnamate)

A lot of the ingredients not approved by the FDA are relatively new and developed to absorb UVA.

Melanin

The hormone alpha-melanocyte stimulating hormone is made when the body is exposed to sunlight and is responsible for the development of the pigment melanin. Research is being done to create stable artificial forms of the hormone. A promising candidate, melanotan, might be useful in the prevention of skin cancer, by causing tanning without the need for exposure to dangerous levels of UV.

Possible adverse effects

Some individuals can have mild to moderate allergic reactions to certain ingredients in sunscreen, particularly the chemical benzophenone, which is also known as phenyl ketone, diphenyl ketone, or benzoylbenzene. It is not clear how much of benzophenone is absorbed into the bloodstream, but trace amounts can be found in urinalysis after use.

Sunscreens are effective in reducing sunburn, but not necessarily the risk of cancer. A study published in April 1992, entitled "Could sunscreens increase melanoma risk?" reported that the greatest increase in melanoma occurred in those regions where sunscreen use is most prevalent. The authors point out that "the SPF of sunscreens concerns solely their ability to absorb ultraviolet B (UVB) light. Even sunscreens with high SPF factors can be completely transparent to ultraviolet A (UVA), which includes 90 to 95% of ultraviolet light. UVA blocking ingredients, which have commonly been added to most sunscreens since 1989, block only half the UVA spectrum and provide a protection factor against delayed UVA induced erythema of only 1.7 at usual concentrations. Both UVA and UVB have been shown to mutate DNA and promote skin cancers in animals. UVA also penetrates deeper into the skin than UVB... two studies suggest that sunscreens may not be effective in preventing skin cancer. A large case-control study showed higher risks of melanoma in men who used sunscreens, and a large prospective study showed a higher incidence of basal cell carcinoma in women who used sunscreens."

Recently, there has been increased attention to the possibility of adverse health effects associated with the synthetic compounds in most sunscreens. Recent studies found that some sunscreens generate harmful compounds that might promote skin cancer. The three commonly used ultraviolet (UV) filters -- octylmethoxycinnamate, benzophenone 3, and octocrylene -- eventually soak into the deeper layers of the skin after their application, where they act as photosensitizer and thereby amplify the free radical production from UV-light (indirect DNA damage). UV rays absorbed by the skin can generate harmful compounds called reactive oxygen species (ROS), which can cause skin cancer and premature aging. The researchers found that once the filters in sunscreen soak into the lower layers of skin, the filters react with UV light to create more damaging ROS. To reduce ROS generation and damage, the researchers recommend reapplying the sunscreen often, which will replenish the sunscreen which has penetrated the skin. Future possibilities may include the development of sunscreens which stay at the surface of the skin, or mixing sunscreens with antioxidants that can neutralize ROS.

A significant reduction in sun exposure inhibits the production of vitamin D. The use of sunscreen with a sun protection factor (SPF) of 8 inhibits more than 95% of vitamin D production in the skin. However, excessive sun exposure has been conclusively linked to some forms of skin cancer and signs of premature aging. Season, geographic latitude, time of day, cloud cover, smog, skin type, and sunscreen all have an effect on vitamin D production in the skin. Fifteen minutes per day of direct exposure to the sun (i.e. without sunscreen) is a generally accepted guideline to follow for optimum vitamin D production.

See also

• Slip-Slop-Slap - famous Australian sun safety advertising jingle
• "Wear Sunscreen" - a column by Mary Schmich in the form of a speech that became a music single and then made into a music video that became viral on the internet
• Indoor tanning lotion
• Sun protective clothing

External links

• FDA rulemaking history for sunscreens

* FDA monograph on sunscreen

* FDA monograph on dosing, mechanism of action, and photodegradation of sunscreen (PDF file)

• Make sure your sunscreen has The Skin Cancer Foundation's Seal of Recommendation
• Environmental Working Group: June 2007 Searchable Sunscreen Safety Database and Report
• Information on what sunscreens are and how they work from The Skin Cancer Foundation
• Sunscreen protection calculator
• Sun Safety for Babies and Children University of Florida/IFAS Extension Department of Family, Youth and Community Sciences
• Article on UV absorbers not yet approved by the FDA
• The sunscreen myth: How sunscreen products actually promote cancer
• Radiation protectants and their CAS registry number
• Environmental Working Group's Sunscreen safety ratings