Wednesday June 1 2011
Most people do not apply sunscreen thickly enough
“Sun cream guidelines 'leave millions at risk',” reported The Daily Telegraph. According to the article, experts have called the decision of “NHS watchdog” NICE to recommend using factor 15 sunscreen a “blunder”.
The news story is based on an article and editorial in the journal Drugs and Therapeutics Bulletin, which discussed the role of sunscreens in preventing skin cancer. The article is based on available evidence and the opinions of a wide range of healthcare professionals and organisations.
The article acknowledges that sunscreen with a sun protection factor (SPF) of 15 can provide adequate protection if applied correctly. However, it cites several studies that have found that many people do not apply factor 15 thickly enough, and suggests that a practical solution is to use sunscreen with a higher SPF of 30.
NICE (the National Institute for Health and Clinical Excellence) recommends that SPF 15 sunscreen should be sufficient as long as it is applied adequately. If people are concerned that they are not applying factor 15 thickly enough, they should consider using a higher SPF sunscreen, such as factor 30.
Watch the video, right, to see how to apply sunscreen.
Where did the story come from?
The news story was based on an article in the Drugs and Therapeutics Bulletin (DTB), a journal that provides independent reviews of medical treatments and disease management. Articles in the journal are published anonymously as they are written collaboratively and incorporate the views of a wide range of people and organisations. The article was accompanied by a short editorial.
This story has been reported by many news sources. Most of them have focussed on the suggestion that SPF 15 sunscreen “is not enough”, although most also eventually clarified that this is only the case if it is not applied to an adequate thickness.
What kind of research was this?
This narrative review looked at whether sunscreens have a role in preventing skin cancer. The authors say that the risks associated with ultraviolet (UV) radiation, such as skin cancer, mean that it is essential to know whether protective measures such as sunscreen provide a worthwhile benefit.
The articles that are published in the DTB are collaborative efforts, and are “a synthesis of the best available medical evidence with opinions from a wide range of commentators”.
The journal’s website gives a general outline of how these articles are produced. It reports that only data in the public domain is used, and the greatest reliance is placed on randomised controlled trials that are double blinded, systematic reviews or meta-analyses published in peer reviewed journals. They also refer to guidance from national bodies such as NICE and the British National Formulary. The journal’s website says that usually over 40 individuals and organisations comment on each article, including independent experts, general practitioners and pharmacists, the Medicines and Healthcare products Regulatory Agency (MHRA) and the British National Formulary (BNF).
The specific methods used in the identification of the relevant evidence, and which individuals contributed, were not given in the article. Without this information, it is not possible to gauge how likely it is that the search found all relevant pieces of information. This sort of article provides an informed (in this case by a large number of contributors) opinion on the evidence.
What did the research involve?
The review discussed various issues, including the effects of UV radiation on the skin, what is in sunscreens, whether they prevent skin cancers, general measures that can be taken to protect against the sun, how to use and choose a sunscreen, any side effects of sunscreens, and who can have sunscreens prescribed on the NHS.
For each of these issues, the authors gave their conclusions based on the evidence they identified and the comments they received from invited commentators. They also included references to the studies that influenced these conclusions.
What were the basic results?
Effects of UV radiation on the skin
The review noted that most of the harm from sun exposure, including sunburn, photosensitivity and skin cancer, is due to UV radiation. The main points the authors discussed about the characteristics of UV radiation from the sun were:
- Solar UV radiation is made up of UVA (wavelength 315–400 nanometres) and UVB (wavelength 280–315nm).
- It is mainly UVA that reaches the Earth, accounting for 95% of terrestrial UV radiation.
- UVB is mainly responsible for sunburn, but both UVA and UVB can cause skin cancer.
- Exposure to UV radiation at wavelengths of less than 315nm promotes the production of vitamin D in our skin.
- Adequate vitamin D formation occurs below the levels of UV required to cause sunburn.
- There is no standard definition of what the “optimum” level of vitamin D is.
The authors then discussed the three main types of skin cancer – basal cell carcinoma, squamous cell carcinoma and malignant melanoma – and noted that UV radiation is considered to be a major factor for causing these.
What’s in sunscreens?
The review reported that most sunscreens sold in the UK contain three to eight different UV filters that absorb or block UV radiation. It also stated that no sunscreen can filter out all UV radiation.
The SPF of a sunscreen indicates how much longer skin covered with the cream takes to redden in response to UV compared to unprotected skin. It mainly indicates the level of UVB protection offered.
When sunscreens are tested, they are usually applied at a thickness of 2mg of product for each cm2 of skin. At this thickness, an SPF 15 product reportedly limits exposure to about 7% of UVB, and an SPF 30 product to around 3% of UVB.
Sunscreens were originally made to prevent sunburn by blocking UVB, and before 1990 did not contain much to prevent UVA exposure. Since then, UVA filters have become available, but there is no international system of rating UVA protection. In the UK, the “Boots star rating system” is commonly used. This system provides a ratio of UVA to UVB protection, and can only be interpreted in relation to the SPF of the product. At a given SPF, more stars means more UVA protection, but a five-star product with a lower SPF could provide less UVA protection than a three-star product with a higher SPF.
Do sunscreens prevent skin cancer?
The article discussed the evidence on the protection offered by sunscreens. It referred to a large, four-and-half-year randomised controlled trial (RCT) in Australia. The trial found that people who were asked to use a broad-spectrum sunscreen of SPF 15 or above on their head, neck, arms and hands at least three or four days a week developed fewer squamous cell tumours than those who used it at their own discretion. Of those in the sunscreen advice group, 1.1% developed squamous cell tumours per year compared to 1.8% of the group who used the sunscreen at their own discretion. This represented a 40% reduction in risk (rate ratio 0.61, 95% confidence interval 0.46 to 0.81). The trial did not find an effect on basal cell carcinoma.
Two studies that carried out a statistical pooling of data from case-control studies have found no association between sunscreen use and risk of malignant melanoma. This may be because the studies were carried out before UVA filters were added to sunscreen, or because people were using sunscreen as a way to stay out in the sun for longer. The RCT from Australia also found no significant effect of sunscreen on new primary melanomas.
Protecting ourselves from the sun
The review reported that for people in the UK who do not have photosensitive disease, the need for sun protection is generally limited to the months between April and September. The authors say that the following measures to reduce UV exposure should be taken:
- limiting exposure to direct sunlight between 11am and 3pm in the UK in summer
- seeking shade
- wearing clothing that provides a high level of absorption of UV
- wearing a hat that shades the face and neck
The review advises that sunscreen should be used in addition to, rather than instead of, these measures.
The authors recommend choosing a sunscreen that can provide good UVA and UVB protection, with a four- or five-star rating and a high SPF, to prevent sunburn. They say that, in theory, a product with SPF 15 should provide adequate protection through the day if used to cover all exposed skin to a thickness of 2mg/cm2. For an adult, this would mean using about 35ml of sunscreen.
However, they say that in reality, people usually apply sunscreen at a thickness of about 0.4-1.5mg/cm2, and give references for the studies that have reported this. If applied more thinly than 2mg/cm2, the protection will theoretically be less than expected based on the SPF. To counter this, some experts suggest applying two coats of sunscreen 15-30 minutes before sun exposure and 15-30 minutes after sun exposure, while others suggest using a higher SPF (30 or more). The article suggests that using a higher SPF is probably more practical.
The article is accompanied by an editorial that questions NICE’s recommendation for using SPF 15 sunscreen, suggesting that to achieve a coverage of 2mg/cm2 is “almost impossible” and also costly. It suggests that to apply SPF 15 sunscreen appropriately at least every two hours as recommended by NICE, a person would use a 200ml bottle of sunscreen every two or three days.
What about vitamin D?
The article notes that properly applied SPF 15 sunscreen can reduce production of vitamin D in the skin by over 99%. According to the authors, the DTB has previously recommended that people with fair skin should be able to make enough vitamin D from sun exposure to their hands, arms, face or back. Sufficient doses should be obtained from exposure to sunlight for 15 minutes two or three times a week from April to September in the UK. These doses should not cause the skin to go red or burn. People with darker skin will need longer exposure.
How did the researchers interpret the results?
The article concluded that “sunscreens can reduce the amount of solar UV radiation entering the skin, and when used during periods of high sun exposure they help to prevent squamous cell cancer.” However, it says that there is not much evidence about whether sunscreens can protect against either basal cell carcinoma or melanoma.
It suggests that sensible precautions to prevent skin damage during sunny weather in summer include:
- limiting how long you are exposed to the sun
- wearing suitable clothing
- using sunscreens
However, the authors warn that sunscreens should not be used as an excuse for excessive sun exposure. They also say that the protection obtained from sunscreen depends to a large extent on how it is used, and that people often apply it too thinly. They suggest that using a sunscreen with a high SPF of 30 is a way to counteract this.
They also note that, in the UK, some exposure of the skin to sun without sunscreen is important for making vitamin D, but that getting sunburnt should be avoided as it is a risk factor for skin cancers.
This article raises the issue that, although SPF 15 sunscreens should be sufficient to prevent exposure to too much UV radiation from the sun, they may not work properly unless they are applied thickly enough. Some studies have suggested that they are often applied too thinly. Based on this, the article recommends using a sunscreen with a higher SPF of 30.
The article is based on the available evidence and the opinions of a range of individuals and organisations. It is possible that some relevant evidence may have been missed. The article does not say that SPF 15 is not useful, but that it will not work as well if it is not used properly. One solution would be for people to apply the sunscreen as directed (to a thickness of 2mg/cm2 of skin, or about 35ml for adults), but an alternative is to use a higher SPF sunscreen.
This review does not contradict NICE guidance, which recommends that a broad-spectrum sunscreen of at least SPF 15 should be used. NICE notes that SPF 15 should be adequate if applied appropriately, and recommends applying two layers of sunscreen, which is one of the options mentioned in the article for ensuring adequate coverage.
NICE guidance and this article also make the important point that sunscreen should be used in addition to, and not instead of, general protective measures against the sun. They also state that some sun exposure is needed for the body to produce vitamin D.
Overall, this article reminds us that protection from UV radiation is important for reducing our risk of skin cancer. If people feel that they cannot apply SPF 15 thickly enough, they should consider using a sunscreen with a higher SPF. In addition, sunscreen should not be used as an excuse for staying out in the sun too long, and getting burnt should be avoided.