Protect from skin cancer with SPF 30 sunscreen
Posted, Friday, 10 August 2012 01:47  

Ultraviolet (UV radiation) is the main risk factor for most forms of skin cancer. People in sunny countries, such as New Zealand, Australia, tropical countries and parts of the United States are certainly at increased risk. Certainly, many people who live in New Zealand and Australia have fair skin types and are very poorly equipped to cope with lots of UV radiation. The vast majority of them are sun damaged before the age of 18 years of age and yet despite this, many people in this age group enjoy sunbathing to get a tan or alternatively, use sunbeds.


It is now well known that sunbeds are hazardous. Despite this, almost 10% of the United States’ population uses sunbeds or sunlamps each year and 70% of those are Caucasian women between the ages of 16 and 30 years. The sunbed industry has steadily grown over the years.

Most tanning lamps emit 95 to 99% of their light as longwave ultraviolet (UVA) and the typical sunbed user can receive an annual dose of UVA – that is 0.3 to 1.2 times the average annual cumulative dose received from ordinary sun exposure and this can happen with a course given over the space of few weeks. The World Health Organisation classifies sunbeds as being carcinogenic and advises minors to avoid using these devices. The American Academy of Dermatology opposes the use of sunbeds and supports a ban on the non-medical production and sale of indoor tanning devices.

There is good medical evidence that sunbed users are at an increased risk of melanoma and non-melanoma skin cancer and a surprising number of other skin disorders.

Everyone should avoid over-exposure to the sun’s rays. Many people still want to be tanned and the belief that a tan allows one to spend more time in the sun safely and a lack of awareness about the dangers of UV radiation are certainly factors that can contribute to photo damage and an increased risk of skin cancer. It is certainly straightforward and easy to take basic measures to protect against the sun, such as wearing protective clothing, limiting sun exposure during peak daylight hours and avoiding sunbeds. The question of which sunscreen to use is more difficult, as there is a bewildering array of sunscreens that are available and some of the claims made on product labels can be difficult to interpret.

Sunscreens are categorised according to their SPF number, UVA protection, stability and substantivity.

The SPF number is a laboratory measure of sunscreen efficacy. It is defined as the amount of ultraviolet radiation required to produce sunburn on protected skin relative to that of unprotected skin. As it is based on erythema (redness), it is mainly a measure of shortwave ultraviolet radiation (UVB) rather than UVA. The SPF of a product is not related to the duration of UV exposure and also the relationship between SPF and UVB protection is not linear. For example, a sunscreen with an SPF of 15 is able to filter 94% of UVB radiation, whereas an SPF of 30 provides more than 97% protection at an equal UVB dosage. UV radiation dosage depends not only on the duration of exposure, but also the intensity of the UV radiation. Therefore, a sunscreen with twice the SPF number does not necessarily mean that you can stay out in the sun twice as long before developing sunburn. There are now almost twenty sunscreen filters that are available for use in products.

It is known that UVA causes significant immunosuppression, so sunscreens with a so-called “broad spectrum” of activity protect against UVA and this must be one where the critical wave length is greater than or equal to the longer end of the UVA band (320-400nm).

Stability of the sunscreen is important for long lasting protection with continuous exposure to UV light, as photo degradation would result in a rapid fall off in the sunscreen’s ability to work properly. Usually, several filters are combined, which leads to a high SPF level and provides broad spectrum UVA and UVB protection and prevents photo degradation.

Sunscreens work in one of two ways. The first mode of action is a chemical absorber, where UV radiation is absorbed by the sunscreen filter and then converted into heat energy. The second is by reflection and these agents include microfined zinc or titanium.

Substantivity is a sunscreen’s ability to remain effective under adverse conditions, such as exposure to water and sweat.

As far as the use of sunscreen is concerned, most people only use approximately one third of the amount of sunscreen required to achieve enough protection. In general, they are not applied sufficiently frequently and following exposure to water, sand and with vigorous exercise, the efficiency of sunscreens can be much less than measured in laboratory settings. It has been established that in the laboratory, that broad spectrum sunscreens that protect against UVB and UVA are more likely to protect against immunosuppression. A few trials have shown that sunscreens do seem to protect against photoageing and there is now excellent evidence that sunscreens prevent solar keratoses (sun spots), which are pre-cancerous growths usually seen on sun exposed skin but also a form of skin cancer called squamous cell carcinoma.

As yet, there is only weak evidence that sunscreens are effective in preventing basal cell carcinoma and melanoma.

Recent controversies also include the fear that daily use of sunscreen may reduce vitamin D level, as UVB is important in the manufacture of vitamin D in the body. Surprisingly, studies have shown that there is no difference between vitamin D levels of subjects who are regular sunscreen users and those who do not. Nonetheless, it would be advisable for people in middle age or old age who are very punctilious about using sunscreens and protecting their skin to get their vitamin D levels checked. Supplemental vitamin D may be given if necessary.

Infants and toddlers are at high risk of UV damage and skin cancer. Children’s skin is thinner than adults and has lower concentrations of melanin, which protects against ultraviolet light. Extra care must therefore be taken to protect children from UV exposure. Children under one year of age should be kept out of sunlight where possible and a broad spectrum sunscreen with an SPF of at least 30 should be used to any unprotected skin.

A good start with sunscreen use, is simply to use a combined sunscreen and moisturiser first thing in the morning (no moisturiser for those with oily skin) and make this a regular habit. More sunscreen can be used again during the day if necessary.



Christchurch Dermatology does not undertake internet consultations.

The contents of this website and this blog are not intended as medical advice. If you have any concerns or problems with your skin, or treatment of skin conditions, see a dermatologist for further advice.

Posted in: Skin Care | Tagged with: cancer Dermatology
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