Between 1986 and 2011, more than 12 research studies were done to assess the effectiveness of sunscreens in preventing skin cancer. Most of these have been ‘observational’ studies containing only 8 – 18 people and using sunscreens with very low SPF ratings.
An observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher. While these studies provide useful information and help formulate hypotheses, only data from randomised clinical trials (RCT) can be used to make definitive statements.
Randomized controlled trials (RCTs) are considered the gold standard for clinical research. To date there has only been one RCT on sunscreen use, published in 2011. In this study, 1,621 randomly selected residents of Nambour, a township in Queensland, Australia , were observed for 14 years. They were randomly assigned either to a group wearing sunscreen every day, or a group wearing sunscreen at their own discretion. This study provides a wealth of information on the efficacy of sunscreen in preventing melanoma.1
Recently, a review of all recent sunscreen studies was carried out in Australia to answer this important question: Does sunscreen use prevent melanoma?
The 2011 Nambour study showed that sunscreen users develop melanoma at half the rate of non-sunscreen users. It also proved that ultraviolet radiation is the primary cause of DNA mutations that lead to melanoma.
UVB is a short ultraviolet wavelength that causes redness and sun burn. All studies reviewed showed that UVB exposure mutates the DNA in our skin cells. Skin biopsies showed obvious photo lesions in DNA (lesions characteristic of UV damage). While the body can repair a certain amount of damage itself, we are exposed to so much sunlight that any photo lesions that aren’t repaired develop permanent mutations. Melanomas have more UV specific mutations than any other cancer.
Sunscreen use prevents 100% of DNA damage.
Other parameters of skin cells were studied and the overall conclusion is that ‘modern sunscreens prevent biological damage to human skin when applied before UVR [ultraviolet radiation] exposure.’ 2
Professor David Whiteman of QIMR Berghofer Medical Research Institute in Queensland says that theoretically, we can prevent 33% of melanomas by 2017 if sunscreen is worn on all exposed skin every single day. 2
There is overwhelming evidence to support this statement. Ideally, sunscreen (SPF30) should be applied to all exposed skin every single day. However, researchers and health authorities have chosen a more pragmatic approach to hopefully encourage more people to use sunscreen regularly.
When to apply sunscreen to prevent skin cancer
While it is possible to sustain DNA damage from UVR during the early morning and late afternoon, a consensus statement for Australia and New Zealand has been agreed upon.
Sunscreen for everyday activities.
When the UV index is forecast to reach 3 or above, it is recommended that sunscreen is applied every day to the face, ears, scalp if uncovered, neck and all parts of the body not covered by clothing.
Ideally this would form part of the morning routine.
Does sunscreen use lead to Vitamin D deficiency?
More research out of QIMR in Australia looks at whether we do, in fact, have an epidemic of low Vitamin D, as some have claimed.
However, agreeing on a ‘normal threshold’ for Vitamin D is tricky. Recommended Vitamin D levels can be anything from 50 nmol/l upwards and the threshold varies from country to country.
Our bodies are really good at making Vitamin D from only a very small amount of sun exposure.2 Clothing reduces our ability to make Vitamin D and some skin must be uncovered for a short period (less than 6 minutes) in order for Vit D synthesis to occur.
Associate Professor, Rachel Neale, discusses the latest research:
Exposure of the skin to ultraviolet (UV) radiation is the main risk factor for skin cancer, and a major source of vitamin D, in many regions of the world. Sun protection messages to minimize skin cancer risks but avoid vitamin D deficiency are challenging, partly because levels of UV radiation vary by location, season, time of day, and atmospheric conditions. The UV Index provides information on levels of UV radiation and is a cornerstone of sun protection guidelines. Current guidelines from the World Health Organization are that sun protection is required only when the UV Index is 3 or greater. This advice is pragmatic rather than evidence based. The UV Index is a continuous scale; more comprehensive sun protection is required as the UV Index increases.
There have been calls to revise the UVI scale itself to better reflect the extreme values that can occur outside Europe. For example, the maximum category reported is currently 11+, but in some locations the UVI can be more than twice as high as this. The use of smartphone apps (e.g., GlobalUV, uv2Day, Uv-indeks) that give information about how the UVI varies throughout the day, along with appropriate messaging, have the potential to facilitate education on the meaning and significance of the UVI that had previously been lacking. 3
Scientists and researchers are currently exploring the possibility of using sunlight exposure in a very measured way in order to achieve sufficient Vitamin D synthesis and at the same time, reduce the amount of DNA damage our skin cells receive when exposed to UVR (UV radiation). One possibility is very brief periods (5 – 6 minutes only) of exposure to sun with minimal clothing and no sunscreen 2 to 3 times a week. Because this is not going to suit a lot of people who are unable to fit this in to their daily schedules, for now, following the UV Index is the most appropriate guide.
- J Clin Oncol.2011 Jan 20;29(3):257-63. doi: 10.1200/JCO.2010.28.7078. Epub 2010 Dec 6.
Reduced melanoma after regular sunscreen use: randomized trial follow-up.
- Sunscreen Summit
March 19 – 20, 2018
QIMR Berghofer Medical Research Institute, Brisbane Australia