Sun protection

^{Figure 1: A combination of the five sun protection measures is recommended: Slip on clothing, Slop on SPF50 or higher sunscreen, Slap on a hat, Seek shade and Slide on sunglasses.}

^{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.^[1] However, because UV damage accumulates over time, Cancer Council recommends that outdoor workers or those working near highly reflective surfaces use sun protection year round, even 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 long clothing 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 adults do. 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 reducing recreational sun exposure at any age.^[6][7]

A nationally representative survey of Australian adolescents’ and adults’ sun protection in 2016-17 found that on a summer weekend:^[8]

• The most common sun protective behaviour used by adolescents was using sunscreen with a sun protection factor (SPF) of at least 30 (40%) and wearing a hat (38%), followed by staying mostly in the shade (23%)
• Less than one-quarter of adolescents reported that they wore ¾ length or longer leg-cover or sunglasses (both 21%) or a ¾ length or long-sleeved top (10%)
• The most common sun protective behaviours among adults were wearing sunglasses (61%), wearing a hat (49%) using sunscreen with SPF15 or higher (42%) and wearing ¾ length or long leg-cover (36%).

A nationally representative survey of Australian adults’ sun protection in January 2019 found that on the previous summer weekend:^[9]

• The most common sun protection behaviours among adults were wearing sunglasses (57%), using sunscreen with SPF30 or higher (37%) and wearing ¾ long leg cover (29%)
• Less than one-quarter of adults reported that they wore a cap or hat other than a wide-brimmed hat (22%), and approximately one-quarter of adults reported that they wore a wide-brimmed hat (27%).
• Approximately one-quarter reported that they wore a ¾ or long-sleeved top (26%).

Trends in Australians’ sun protection behaviours

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

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 of 50 or above offering "excellent" levels of protection by blocking out ≥98% of UV radiation. In Australia, UV-protective clothing must meet the Australian 2020 Standard, which specifies that garments must be tested by an accredited lab and adhere to minimum body coverage requirements, 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]

Sunscreen

Sunscreen is one of the most common methods of sun protection. SunSmart recommends SPF50 (or higher) broad spectrum, water-resistant sunscreen. Sunscreens are lotions, creams, gels or aerosols that prevent UV-induced skin damage.

Active sunscreen ingredients work in two ways - scattering and /or absorbing ultraviolet (UV) radiation to help stop it from reaching the skin.^[14][15] Some sunscreens utilise both absorbing and scattering ingredients. Examples of scattering ingredients include Zinc Oxide and Titanium Oxide.^[15] Absorbing ingredients include cinnamates (UVB filter), oxybenzone (UVA) and terephthalylidene dicamphor sulfonic acid (a UVA and UVB filter).^[14] Sunscreen formulations composed primarily of scattering active ingredients 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] and it is estimated that daily sunscreen use over 30 years would result in close to $40 million of savings in societal costs per 100,000 persons in Queensland^[18]

Another evaluation of an intervention promoting sunscreen as a means of preventing skin cancer showed that the intervention saved the government money but imposed a small cost on society as a whole for these improved health outcomes. If health providers, governments, and individuals were collectively willing to pay and contribute to preventing skin cancer, this sunscreen initiative would cost society an outlay of AUD$4224 per skin cancer prevented over a 5-year period, or AUD$1.03 per person annually. Given that this investment is a fraction of what individuals in developed nations alone pay for cosmetic skin-care products, this expense seems extremely worthwhile. For governments in a publicly funded health system that incur the cost of skin cancer medicine, this intervention yielded considerable cost savings within 5 years under a range of cost scenarios.^[17]

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.^[19]

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.^[19] 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.^[20]

Properly applied, (the ‘teaspoon rule’ of 2mg/cm2^[21][22]) 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).

Broad-spectrum

Sunscreens that are proven to be protective against both UVB and UVA are referred to as broad-spectrum.^[20] Broad-spectrum protection is a requirement for primary and secondary sunscreens regulated by the Therapeutic Goods Administration (TGA). Sunscreens tested according to the 2021 Standard must achieve a UVA protection factor equal to as least one-third of the labelled SPF.^[19]

In 2012 the ‘per cent transmission test’ for UVA protection was replaced 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]

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.^[23] Products can only be listed on the register if they comply with the Australian/New Zealand Standard for sunscreen products (AS/NZS 2604:2021).^[19]

The 2021 standard completes the transition from Australian and New Zealand test methods to determine broad spectrum, SPF, and water resistance to internationally recognised ISO standards.^[19]

Under the 2021 standard (AS/NZS 2604:2021), sunscreens meeting TGA testing standards may be labelled with a maximum SPF50+. 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.

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.^[24] As a result, sunscreen users achieve an SPF of between 50-80% less than that specified on the product label.^[25],[26] In order to achieve the specified SPF, people should apply 2mg sunscreen to each square centimetre of exposed skin. This equates to approximately 35mL (seven teaspoons) per application for an adult.^[22] Some researchers have recommended that people apply slightly more than this: 45mL in the form of nine 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.^[27]

Sunscreen needs to be applied 20 minutes before going outside^[28] and reapplied every two hours thereafter.^[29] 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.^[28]

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.^[30]

People living in Australia or New Zealand are advised to apply sunscreen every day on days when the UV is forecast to be 3 or above.^[31]

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.

Aerosol sunscreens are more difficult to apply at the recommended dosage,^[32] and a significant proportion of product may be lost to wind before adhering to the skin. A 2021 Queensland study^[33] found that among the products tested, the proportion of sunscreen lost due to typical wind conditions ranged from 32%-79% for 10 kph and 28–93% for 20 kph wind.

Cancer Council does not recommend the use of aerosol sunscreens for the above reasons^[34] and the TGA has planned a review of the efficacy of aerosol sunscreen^[35]

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.^[36]

Randomised studies conducted in Nambour, Queensland have shown that when sunscreen is used regularly, it is effective in reducing melanoma^[37] and squamous cell carcinoma (SCC), but not basal cell carcinoma (BCC).^[38][39] These studies are considered to represent the highest-quality evidence to date.^[40]

It has been argued that a significant reduction in BCC risk was not evident in Green and colleagues’ 1999 randomised controlled trial,^[38] due to the critical period for BCC risk being earlier in life^[41] 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.^[42] That a non-significant decrease in BCC risk was found is likely indicative of an association with sunscreen use.^[39] Further, the sunscreen used in the study^[38] likely lacked in stable UVA coverage compared with current sunscreen formulations, with the basal skin layer being most vulnerable to UVA radiation.^[43][44] This suggests another possible reason why a significant BCC risk reduction was not observed.^[42]

Routine sunscreen use has been associated with a reduction in melanoma risk.^[45][46][47] A comprehensive study of cancer prevention in Australia estimated that, in 2010, more than 1700 cases of melanoma and 14,190 squamous cell carcinomas (a common non-melanoma skin cancer) were prevented by long-term sunscreen use.^[48] Under a plausible public health intervention scenario comprising incremental increases in sunscreen prevalence over a 10-year period, it was estimated that cumulatively to 2031, 28,071 fewer melanomas would arise in Australia (PIF 10%).^[49]

Barriers to sunscreen efficacy include incorrect application^[50] by either applying less than the recommended amount^[51] or applying in a non-uniform layer,^[30] failing to reapply^[28] or sunscreen removal caused by water or abrasion.^[51][52] 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.^[53][54]

Sunscreen use is also protective against solar keratoses^[55] and photo-ageing (premature skin ageing due to sun exposure such as wrinkles and skin discolouration).^[56]

Nanoparticles

Micro-particle metal oxide (TiO2 and ZnO) scatter UV radiation away from the skin and may give an opaque appearance on application. In contrast, nanoparticles are less opaque when spread on skin,^[57] making sunscreen use more cosmetically acceptable.^[58] Titanium dioxide and zinc oxide based sunscreens are also less likely to cause skin irritation and sensitisation.^[16]

The safety of nanoparticles in sunscreen has been comprehensively studied. Incidental ingestion, as from a sunscreen spray, is likely to present more of a risk than topical absorption. However, a review by Nohynek and colleagues suggests nanoparticles may not have the capacity for systemic absorption (i.e. circulation throughout the body).^[59] A 2013 study showed 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.^[60]

Sunscreen formulas and their components are regulated through the TGA. In 2016, the TGA updated their review of the scientific literature in relation to the use of TiO2 and ZnO in sunscreen.^[61] It states that the current weight of evidence suggests that TiO2 and ZnO nanoparticles do not reach viable skin cells (even in compromised skin) or the general circulation, but rather remain on the skin surface and in the outer layer of the stratum corneum. This suggests that systemic absorption, hence toxicity, is highly unlikely.^[61]

The review notes that antioxidant compounds/coatings are used in sunscreen to prevent generation of reactive oxygen species (ROS). However, free radicals (a type of ROS) may be generated by coated Ti02 nanoparticles in the presence of swimming pool water.^[61]

The review concludes that, on current evidence, neither TiO2 nor ZnO nanoparticles are likely to cause harm when used as ingredients in sunscreens and when sunscreens are used as directed. The current state of knowledge strongly indicates that the minor risks potentially associated with nanoparticles in sunscreens are vastly outweighed by the benefits that nanoparticle-containing sunscreens afford against skin damage and, importantly, skin cancer.^[61]

Adequate vitamin D

Regular use of sunscreen when the UV Index reaches three or above should not greatly decrease vitamin D levels over time.^{[62][63][64][65]} 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.^[65] In addition, it is thought that vitamin D synthesis requires only modest doses of sunlight to be effective^[66] and most people get sufficient UV exposure from incidental outdoor exposure.

A 2019 review^[67] concluded ‘There is little evidence that sunscreen decreases 25(OH)D concentration when used in real-life settings, suggesting that concerns about vitamin D should not negate skin cancer prevention advice’. The review also noted however that there have been no trials of the high-SPF sunscreens that are now widely recommended.

Hats

A broad-brimmed hat with a brim of at least 7.5cm, which shades the face, ears and neck,^[68] can block more than 50% of UV radiation to the eyes.^[69] 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.^[68]

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).

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 can reduce UV exposure by up to 75%.^[70]

Shade fabric designed for human protection is assigned a UVE (Ultraviolet Effectiveness) rating, expressed as a percentage. Since 2018, a human protection rating has also been applied which is linked to the fabric UVE and indicates the level of protection provided to humans.^[71]

When shade fabric is to be used for human protection purposes, such as shade structures, the calculated UVE results do not take into account important factors that may decrease the effective UVE, such as design features, height and size of the shade structure, the distance of the shade fabric from the subjects, the effect of direct and indirect solar UVR and the physical location of the subjects within the shade structure. For this reason, the UVE value determined for the classification of the fabric does not indicate the actual reduction of solar radiation by a structure incorporating that fabric.^[71]

Shade does not provide 100% protection. It is therefore recommended to always combine shade with clothing, a broad-brimmed hat, sunglasses and sunscreen.

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.^[72]

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).^[73] Chronic over-exposure may lead to permanent damage such as squamous cell cancers on the conjunctiva,^[74][75][76] skin cancer around the eyes^[5][77] and eyelids, and possibly some varieties of ocular melanoma (although evidence remains inconclusive).^[78][79][80] Other long-term damage to the eyes may include cataracts,^[81] macular degeneration,^[81][82] pterygium (an overgrowth of the conjunctiva on to the cornea), and climatic droplet keratopathy (cloudiness of the cornea).^[83]

Wearing both a broad-brimmed hat and sunglasses that meet Australian Standard^[84] can reduce UV radiation exposure to the eyes by up to 98%.

In Australia, sunglasses and fashion spectacles are required by the Consumer Goods (Sunglasses and Fashion Spectacles) Safety Standard 2017 to be tested to the Australian/New Zealand Standard AS/NZS 1067.1:2016 Eye and face protection - sunglasses and fashion spectacles prior to sale.^[85]

Cancer Council Australia recommends wearing close-fitting, wraparound style sunglasses that meet the Australian/New Zealand Standard for sunglasses (categories 2, 3 and 4).^[86] A close-fitting, wrap-around style is recommended, as it provides further protection from the 40% of UV that reaches the eye due to peripheral light.^[87] Sunglasses may also be labelled UV 400 and block at least 95% of UV between 190 and 400nm.^[84]

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.^[88] UVB radiation is completely blocked by most types of glass.^[89] The degree of UVA transmission depends largely on the type of glass.^[88] 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%).^[90]

Glass in vehicles

Laminated glass, required for windshield glass in vehicles sold in Australia,^[91] offers better UVA protection than tempered glass, which is used in car rear and side windows.^[88] Laminated glass filters out all UVB and 98% of UVA radiation.^[92] Tempered glass side windows also filter out all UVB but only 21% of UVA.^[88] However, glass treated with a UV-absorbing window film filters 99.6% of total UVR.^[88]

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Last modified: 12 August 2022