Sun protection

From Skin Cancer Statistics and Issues


Sun smart icon

Figure 1: A combination of the five sun protection measures is recommended: Slip on clothing, Slop on SPF30 or higher sunscreen, Slap on a hat, Seek shade and Slide on sunnies.

Images provided by Cancer Council Australia.


Sun protection in the form of clothing, sunscreen, broad brimmed hats, shade and sunglasses is recommended during times when the UV (ultraviolet) Index reaches 3 and above. This is the threshold at which UV radiation can damage skin, according to the International Commission on Non-Ionizing Radiation Protection (ICNIRP 2012).[1] Safe Work Australia also recommends sun protection for workers who spend extended periods of time outdoors, even on days when the UV Index is below 3.[2]

Infants and toddlers (up to 4 years of age) are particularly vulnerable to UV radiation-induced changes in the skin due to lower levels of melanin and a thinner stratum corneum (the outermost layer of skin). Therefore, limiting sun exposure and using clothing cover while outdoors is recommended for infants and toddlers regardless of skin type.[3] Very young babies (less than 6 months of age) absorb more of any chemical applied to the skin than occurs for adults. For this reason, the Australasian College of Dermatologists does not recommend widespread and regular use of chemical sunscreens for babies less than six months of age.[4] However, to date there have been no documented reports of harmful side effects that have occurred as a result of sunscreen absorption among babies.[4]

Sun protection is recommended at all ages, as skin cancer risk is reduced at whichever age sun protection is used.[5] High sun exposure in the first 10 years of life more than doubles melanoma risk, [6] while intense, intermittent sun exposure (for example, in the form of sunbathing vacations) during each decade up to 29 years of age, increases risk of melanoma by over one-and-a-half times.[7] Every additional decade of high sun exposure or solarium use increases the risk of melanoma. The risk of melanoma is reduced by by reducing recreational sun exposure at any age.[6][7]

A nationally representative survey of Australian adolescents’ and adults’ sun protection in 2010-11 found that on a summer weekend[8]:

  • The most commonly used sun protective behaviour by adolescents was use of sunscreen with a sun protection factor (SPF) of at least 15+ (37%), followed by ¾ length or longer leg-cover (28%)
  • Less than one-quarter of adolescents reported that they wore a hat, cap or visor (23%), or sunglasses (24%) or were mostly in the shade while outdoors (21%)
  • Adults’ sun protection compliance was generally better than that of adolescents
  • The most common sun protective behaviours among adults were wearing sunglasses (57%), wearing a hat, cap or visor (45%) and wearing ¾ length or long leg-cover (44%)
  • Similar to adolescents, 36% of adults reported wearing sunscreen on the weekend that they were outdoors.


Trends in Australians’ sun protection behaviours

For trends in Australians' sun protection behaviours since 2003-04, see here.

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Clothing

One of the best barriers between skin and the sun is clothing. Sun protective clothing includes long pants and collared, long-sleeved shirts, which cover as much skin as possible. Clothing can provide protection by absorbing and reflecting UV radiation that strikes the surface of the fabric. Ultraviolet Protection Factor (UPF) ratings are based on how much UV radiation passes through non-stretched, dry material. The UPF represents the factor by which UV radiation exposure is reduced (e.g. a garment with UPF 50 allows one-fiftieth of UV radiation to pass through it). UPF for clothing ranges from 15 to 50+ with ratings above 40 offering "excellent" levels of protection by blocking out ≥97.5% of UV radiation.[9] In Australia, UV-protective clothing has to meet the Australian and New Zealand 1996 Standard, which specifies that garments must be lab-tested by the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) in order to display a UPF label.[10]

Fabrics do not need to be UPF rated to provide protection from UV. When wearing garments that do not have a UPF label, light weight, closely woven and dark coloured clothing is recommended.[11][12] Designs that maximise body coverage - for example shirts with long sleeves and collars - are also recommended.[13]

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Sunscreen

Sunscreen is one of the most common methods of sun protection. SunSmart recommends SPF 30 (or higher) broad spectrum, water-resistant sunscreen. Sunscreens are lotions, creams, gels or aerosols that prevent UV-induced skin damage. Sunscreens protect against UV radiation through the use of filters, either inorganic/physical or organic/chemical, that absorb within the UV range.[14],[15] Inorganic filters are composed of minerals - most commonly the metal oxides titanium dioxide or zinc oxide, which screen both UVA and UVB.[15] Organic/chemical filters are composed of various compounds such as cinnamates (UVB filter), oxybenzone (UVA) and terephtalylidenedicamphor sulfonic acid (a UVA and UVB filter).[14] Sunscreen formulations composed primarily of inorganic/physical filters do not penetrate as deeply into the skin[14], however, this makes them less likely to cause irritation/sensitisation.[16]

Sunscreen should be stored below 30C and not used past expiry date. Sunscreen should be used in conjunction with other sun protection such as staying in the shade, wearing covering clothing, a broad-brimmed hat and sunglasses.

Regular sunscreen use is a cost-effective approach to skin cancer prevention.[17] An intervention promoting regular sunscreen use to prevent skin cancer showed that it would save the government money and only impose a small cost on society as a whole for these improved health outcomes. According to the economic evaluation, if all relevant parties were committed, the sunscreen initiative would cost the Australian government an outlay of AUD$4224 per skin cancer prevented over a 5-year period, or AUD$1.03 per person annually.[17]

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Sun protection factor

The higher a sunscreen’s sun protection factor (SPF) the more UVB radiation it filters. Sunscreens labelled broad-spectrum are also protective against UVA.[18]

The SPF of a sunscreen is determined as the ratio of time taken for a minimal erythema (a perceptible reddening of the skin) to appear when 2mg/cm2 sunscreen is applied, in comparison to the time it takes to reach the minimal erythemal dose (MED) without sunscreen.[18] As such, SPF is only a measure of protection under idealised laboratory conditions and against UVB radiation (the wavelength primarily responsible for erythema). SPF does not take into account UVA or immunosuppression spectra.[19]

Properly applied, (the ‘teaspoon rule’ of 2mg/cm2[18][20]) SPF30 sunscreens filter out 96.7% of UVB, while SPF50 filters out 98%.[19] Despite an increase in protection level, SPF50+ sunscreen must continue to be reapplied every two hours to maintain the optimum level of protection, and used in conjunction with other sun protection (clothing, hats, shade, and sunglasses).

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Broad-spectrum

Sunscreens that are proven to be protective against both UVB and UVA are referred to as broad-spectrum.[19] Broad-spectrum protection is now a requirement for primary and secondary sunscreens regulated by the Therapeutic Goods Administration (TGA). The level of UVA protection must match the level of UVB protection.[19]

The 2012 Standard replaced the ‘per cent transmission test’ for UVA protection with the ISO 24443 procedure, which involves prolonged irradiation of sunscreen to ensure photo-stability (i.e. minimal degradation during sun exposure), and requires that UVA is absorbed uniformly throughout the UVA spectrum (n.b. this uniformity requirement also applies to SPF/UVB radiation).[19]

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Sunscreen standard

The TGA regulates primary sunscreens as well as some secondary sunscreens (i.e. cosmetics containing sunscreen agents that are at least SPF15). Sunscreens with an SPF rating of 4 and above are listed on the Australian Register of the TGA.[21] Products can only be listed on the register if they comply with the Australian/New Zealand Standard for sunscreen products (AS/NZS 2604:2012).[18]

Under the new standard (AS/NZS 2604:201218) effective 9 November 2012, sunscreens meeting TGA testing standards may be labelled as SPF50+, whereas previously SPF30+ was the highest level of protection manufacturers were able to claim. Sunscreens labelled between SPF15-SPF29 may no longer claim to be 'high protection', as this category is now assigned to sunscreens between SPF30-50. Only SPF50+ sunscreens may be labelled 'very high protection'. Sunscreens regulated by the TGA must provide broad-spectrum protection against UVA as well as UVB radiation. UVA protection testing is also more stringent, with improved accuracy and reproducibility through use of the ISO 24443 in-vitro procedure.

Under the 2012 standard, continued sale of already registered sunscreens labelled as SPF30+ is permitted indefinitely. Some sunscreens labelled SPF30+ may offer SPF50+ levels of sun protection, however these products must undergo re-testing to be re-branded SPF50+. Newly-registered SPF30+ sunscreens must pass the new broad-spectrum test.[18]

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Proper application

Prior to applying sunscreen, check and follow the use-by date stated on the packaging and store sunscreen below 30°C.

Most people apply far less sunscreen than is recommended by manufacturers.[22] As a result, sunscreen users achieve an SPF of between 50-80% less than that specified on the product label.[23],[24] In order to achieve the specified SPF, people should apply 2mg sunscreen to each square centimetre of exposed skin. This equates to approximately 35ml per application for an adult.[20] It is recommended that people apply slightly more than this: 45mL (equivalent to a shot glass/golf ball) in the form of 9 teaspoons (5mL each); one teaspoon of sunscreen applied to the face/head/neck, two teaspoons for the torso, one teaspoon to each arm/forearm and two teaspoons to each leg.[25]

Sunscreen needs to be applied 20 minutes before going outside[26] and reapplied every two hours thereafter.[27] Reapplication of sunscreen 15-30 minutes after going outdoors may also be beneficial, as people are not likely to apply the required amount of sunscreen upon first application. [26]

According to a simulation study, typical sunscreen application - less than the recommended amount (3-6mL per body part) and non-uniformly application - will often result in sunburn and skin damage.[28]

No sunscreen provides full protection. Therefore sunscreen should always be used in combination with other sun protection measures – clothing, broad-brimmed hats, shade and sunglasses.

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Evidence of efficacy

When applied properly, sunscreen protects against sunburn and tanning. In an experiment irradiating melanocytes and keratinocytes in Caucasian participants, sunscreen was shown to completely block the effects of DNA damage after exposure to 2 MED of solar-simulated UV radiation.[29]

Randomised studies conducted in Nambour, Queensland have shown that when sunscreen is used regularly, it is effective in reducing melanoma[30] and squamous cell carcinoma (SCC), but not basal cell carcinoma (BCC).[31][32]

However, it has been argued that a significant reduction in BCC risk was not evident in Green and colleagues’ 1999 randomised controlled trial,[31] due to the critical period for BCC risk being earlier in life[33] than the age at which the intervention occurred. In addition, the long time lag between sun exposure and developing BCC as compared with the 4.5 end-point and eight-year extended study follow-up may have been insufficient.[34] That a non-significant decrease in BCC risk was found is likely indicative of an association with sunscreen use.[32] Further, the sunscreen used in the study[31] likely lacked in stable UVA coverage compared with current sunscreen formulations, with the basal skin layer being most vulnerable to UVA radiation.[35][36] This suggests another possible reason why a significant BCC risk reduction was not observed.[34]

Routine sunscreen use has been associated with a reduction in melanoma risk.[37] However, there are barriers to sunscreen efficacy such as incorrect application[38] by either applying less than the recommended amount[39] or applying in a non-uniform layer,[28] failing to reapply[26] or sunscreen removal caused by water or abrasion.[39][40] It has also been reported that sunscreen use may encourage extended sun exposure among sunbathers and increases the risk of skin cancer when used in in this way.[41][42]

Sunscreen use is also protective against solar keratoses[43] and photo-ageing (premature skin ageing due to sun exposure such as wrinkles and skin discolouration).[44]

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Nanoparticles

Nano, as opposed to micro-particle metal oxide (TiO2 and ZnO) ‘physical’ sunscreens, are less opaque when spread on skin,[45] eliminating this as a barrier to sunscreen use by being more cosmetically acceptable.[46] Titanium dioxide and zinc oxide based sunscreens are also less likely to cause skin irritation and sensitisation.[16]

The current weight of evidence suggests that topically applied (insoluble) titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles (NPs) do not reach skin cells; rather, they remain on the surface and outer layer of the skin and therefore the risk they pose is negligible.[16][47] However, it is likely that sunscreen nanoparticles can penetrate the stratum corneum (outermost layer of skin) if applied to damaged skin.[48] Incidental ingestion, as from a sunscreen spray, is likely to present more of a risk than topical absorption. However, a recent study suggests NPs may not have the capacity for systemic absorption (i.e. circulation throughout the body).[49] A recent study has shown that a small amount of ZnO nanoparticles can penetrate human skin. However, 50-60% of these are dissolved in as little as 24 hours as a part of a cell-mediated immune response before they reach the bloodstream.[50]

Sunscreen formulas and their components are regulated through the TGA. In 2013, the TGA updated their review of the scientific literature in relation to the use of nanoparticle TiO2 and ZnO sunscreens.[48] As in the previous review,[51] it was determined that antioxidant compounds/coatings used in sunscreen prevent TiO2 from generating reactive oxygen species (ROS), and that TiO2 and ZnO do not penetrate the skin to a degree where they pose a health risk. [48] However, further research is required on the health effects of free radicals, which may be generated by coated nanoparticles in the presence of chlorinated water. [48]

The US Department of Health and Human Services’ ‘Twelfth Report on Carcinogens’ lists compounds that have been proven to cause cancer. This list is updated frequently and has never included the chemicals found in sunscreen, including TiO2 and ZnO.[52]

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Adequate vitamin D

Regular use of sunscreen when the UV Index reaches three or above should not greatly decrease vitamin D levels over time.[53][54][55][56] Although sunscreens could almost entirely block the solar-induced production of cutaneous pre-vitamin D3 on theoretical grounds or if administered under strictly controlled conditions, in practice they have not been shown to do so. This is mainly due to inadequacies in their application to the skin and because people using sunscreens may also expose themselves to more sun than non-sunscreen users.[56] In addition, it is thought that vitamin D synthesis requires only modest doses of sunlight to be effective[57] and most people get sufficient UV exposure from incidental outdoor exposure.

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Hats

A broad-brimmed hat with a brim of at least 7.5cm, which shades the face, ears and neck,[58] can block more than 50% of UV radiation to the eyes.[59] Bucket hats with a brim of at least 6cm and legionnaire-style hats with a flap covering the neck are also recommended. Baseball caps are not recommended as they leave the ears, cheeks and back of the neck exposed.[58]

The brim width on bucket hats for children should be suitable for the size of their head and shade their face well (minimum of 5 cm as a guide).

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Shade

Built, natural and portable shade are all recommended for sun protection during peak UV radiation times. Shade is one of the most effective forms of sun protection as it blocks the majority of incidental radiation (direct, non-scattered radiation). Shade structures often reduce UV exposure by up to 75%. Shade structures with a protection factor (PF) of 15 (blocking 93% of UV radiation) or above offer optimal protection against ambient solar UVR[60] (PF is the protection factor representing the ratio of UVR measured in open sun vs. under shade[61]).

Shade, however, does not provide 100% protection. Some of the sun's UV can still reach a person in the shade via reflection off surrounding surfaces. As a rule of thumb if you can see the sky, you are less than fully protected. It is therefore recommended to always combine shade with clothing, a broad-brimmed hat, sunglasses and sunscreen.

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Sunglasses

Exposure to UV radiation over long periods can lead to serious damage to the eyes. If practical, try to protect the eyes all year using sunglasses. The amount of UV reaching the eyes does not correlate well with UV levels, which measure UV reaching an unobstructed horizontal plane, and is instead highly dependent on unique geometry of the ocular region.[62]

Overexposure to UV radiation can cause short-term eye damage in the form of mild irritation, acute photokeratitis (sunburn of the cornea), inflammation, excessive blinking and photophobia (difficulty looking at strong light).[63] Chronic over-exposure may lead to permanent damage such as squamous cell cancers on the conjunctiva,[64][65][66] skin cancer around the eyes[5][67] and eyelids, and possibly some varieties of ocular melanoma (although evidence remains inconclusive).[68][69][70] Other long-term damage to the eyes may include cataracts,[71] macular degeneration,[71][72] pterygium (an overgrowth of the conjunctiva on to the cornea), and climatic droplet keratopathy (cloudiness of the cornea).[73]

Wearing a broad-brimmed hat can reduce UV radiation exposure to the eyes by 50%.[59] Wearing both a broad-brimmed hat and sunglasses that meet Australian Standard[74] can reduce UV radiation exposure to the eyes by up to 98%.[74]

Sunglasses should meet the Australian Standard AS1067:2003 for sunglasses (lens categories 2, 3 or 4) and have an eye protection factor (EPF) of 9 or 10 or be labelled UV400.[74] Darker-tinted lenses reduce glare, but level of tinting does not indicate the level of UV protection. Wearing close-fitting, wrap-around sunglasses is recommended, as 40% of UV reaching the eye is due to peripheral light.[75]

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Window tinting

Glass used in buildings

While glass thickness affects UV radiation transmission, other characteristics such as type and colour of glass should be considered.[76] UVB radiation is completely blocked by most types of glass.[77] The degree of UVA transmission depends largely on the type of glass.[76] A study investigating UVA transmission through different types of building glass, found that laminated glass completely blocked UVA, while highest transmission was observed for annealed glass (74.3%) and tempered glass (71.6%).[78]


Glass in vehicles

Laminated glass, required for windshield glass in vehicles sold in Australia,[79] offers better UVA protection than tempered glass, which is used in car rear and side windows.[76] Laminated glass filters out all UVB and over 80% of UVA radiation (equivalent to UPF50+), transmitting only 2.5% of UV radiation.[80] Tempered glass side windows only block 21% of total UVR, but when glass was treated with a UV-absorbing window film it blocks 99.6%.[76]

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References

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