DO SUNCREENS PROTECT US ?Douglas L. Maslim, MA, BCHIR

Journal Reading

Riska Aulia Rahma

Sunlight stimulates a multitude of important biological effects on skin, causing, amongst other pathological changes, photocarcinogenesis. Sunscreens are designed to provide protection against these harmful properties of ultraviolet radiation, and public health campaigns have been employed to encourage their use.

INTRODUCTION

“Slip, Slop, Slap, Seek and Slide” is one of many campaigns worldwide designed to encourage the use of sunscreens among the public. As the popular belief has been that sunscreens protect us from the damaging effects of the sun, such campaigns have implored us to “slop on the sunscreen” as a key way of gaining such protection

Sunlight stimulates a multitude of important biological effects on skin; causing sunburn,photoaging, photocarcinogenesis, and immune suppression.

Both academic and media interest has centered on the continual rapid rise in the incidence of malignant melanoma – largely due to this form of skin cancer carrying with it the highest mortality rate and affecting the younger demographic.

WHAT IS THE DANGER? Epidemiological studies initially revealed that sunlight is asignificant risk

factor for skin cancer.

Sunlight reaching the Earth's surface is composed of differing wavelengths of the electromagnetic spectrum,ranging from infrared through to visible and UV light. It is the UV portion of the spectrum, specifically UVB and UVA (between 280 and 400 nm), that is the most damaging to our skin.

This UV light is able to cause DNA damage, initiating the formation of genetic mutations which may, for example, progress into the “hallmarks of cancer

UVA constitutes 95% of the UV energy reaching the equator. Its longer wavelength explains why UVA is able to penetrate into deeper layers of the skin than UVB, with a greater percentage penetrating the basal epidermis cells

Recent studies have contradicted previous beliefs that UVA is not significant in the pathogenesis of cancer, with data suggesting a role for UVA in melanoma. UVA potentiates the carcinogenic effects of UVB and stimulates generation of carcinogenic free radicals within the skin.

In contrast to UVA, only a small proportion of UV light that penetrates our skin is of the UVB spectrum. Despite this, the specific properties of UVB implicate it as the predominant factor in the pathogenesis of melanoma, basal cell, and squamous cell skin cancers.

UV radiation, particularly UVB, may stimulate the inflammatory erythema commonly referred to as sunburn, and the public commonly attempt to avoid sunburn by applying sunscreen. Importantly, evidence shows a strong positive correlation between a history of sunburn and the incidence of both melanoma and non-melanoma skin cancers.

The high mortality rate of melanoma highlights the importance of protecting ourselves from the sun. Melanoma disproportionally affects the younger population,with one-third of cases occurring in those under 55.

HOW SHOULD WE USE SUNSCREEN? The ideal sunscreen would prevent 100% of all wavelengths of UV radiation from penetrating the skin and would provide long-term protection without the need for reapplication.

There are many different types of sunscreen, each containing a combination of agents with different chemical groups, designed to either absorb or reflect a proportion of the incoming UV energy. A significant factor affecting the protection sunscreens provide is the sun protection factor (SPF)

Behavior is a key factor: individuals who apply a higher SPF may become complacent and so tend to spend more time in the sunlight (including at noon when doses of UV radiation are highest), while reapplying the sunscreen less frequently.

Of additional importance is the timing of application and reapplication. Although the exact recommendations vary between studies, it is clear that sunscreen is not applied often enough by the general public and that applying sunscreen once is insufficient. One recommendation is that sunscreen should be applied 30 minutes before going out into the sun and then reapplied both 30 minutes after sun exposure begins and after any activity that may remove the sunscreen.

PROTECTION AGAINST SKIN CANCER?

A randomized controlled trial found the daily use of sunscreen over 4½ years significantly reduced the incidence of squamous cell carcinoma but not of basal cell carcinoma. More recent studies have had similar results – the risk of squamous cell carcinoma is decreased, but the results for basal cell carcinoma are equivocal.

However, the major controversy surrounds the link between sunscreen and melanoma. Initially, it was assumed that sunscreen would reduce melanoma incidence by blocking harmful UV radiation. However, there has been evidence from case–control studies to suggest that sunscreen is, in fact, a risk factor for melanoma formation; although a quantitative review of the data found no such association. the results of case– control and cohort studies has so far been unhelpful in resolving this debate.

Furthermore, there are other ingredients in sunscreens, which have the potential to cause harm. Retinyl palmitate, a form of vitamin A added to many sunscreens, has been linked with cancer formation. However, current evidence “fails to demonstrate … that retinyl palmitate imparts an increased risk of skin cancer”. This same review concluded that oxybenzone, zinc oxide, and titanium oxide – all found in sunscreens – are unlikely to be harmful

This assessment of the evidence helps us to understand the recent FDA guidelines.28 Only the labels of broadspectrum sunscreens (those passing the standard UVA and UVB protection tests) with an SPF value of at least 15, will state that they not only protect against sunburn but, if used as directed with other sun protection measures, can reduce the risk of cancer and early skin aging. Higher SPF values, up to a maximum of 50+, will indicate a greater level of protection.

CONCLUSION: THE BURNING ISSUE OF SUNSCREEN EDUCATION

The International Agency for Research on Cancer has stated, “sunscreens

should not be the first choice for skin cancer prevention and should not be

used as the sole agent for protection against the sun”.28 Therefore, current

campaigns such as ‘Slip, Slop, Slap, Seek and Slide’ are sending out the

right message: to optimize protection from the damaging effects of the sun

we should not just ‘slop on the sunscreen’ but also ‘slip on a t-shirt, slap on

a hat, seek shade, and slide on sunglasses’. Importantly, none of these

steps is sufficient on their own, and all should be carried out together.

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