By Susanne Martin
All the discussion about SPF numbers, UVA versus UVB rays, and chemical versus mineral sunscreens can make sun protection seem confusing. It’s not. And learning about how sunscreens work can help us make smart decisions when it comes to sun safety.
Ultraviolet (UV) radiation from sun exposure is the primary environmental cause of premature skin aging and most skin cancers, says Anatoli Freiman, medical director of the Toronto Dermatology Centre, who advises to implement sun protection measures year-round. While skin cancer is the most common type of cancer, it is also one of the most preventable.
Of UV radiation’s three wavelengths – UVA, UVB and UVC – UVA and UVB rays are carcinogenic. Dr. Freiman, who is also the chair of the Canadian Dermatology Association (CDA) Sun Protection Program, recommends using a broad-spectrum sunscreen with a Sun Protection Factor (SPF) of at least 30. “SPF indicates the level of protection against UVB and an SPF of 30 protects against about 97 per cent of UVB rays,” he says. “The second consideration is to choose a sunscreen that is broad spectrum, meaning that it protects against both UVA and UVB rays.”
Sunscreens rely on two kinds of filters: chemical and mineral. Chemical filters form a thin, protective film on the skin’s surface that absorbs UV radiation before it penetrates the skin. Mineral sunscreens are insoluble particles that reflect UV rays away from the skin. Some products combine chemical and mineral ingredients.
A Health Canada sunscreen monograph lists 19 active sunscreen ingredients. Of these active ingredients, two are minerals and the rest are chemicals. Each ingredient has its own unique spectrum of protection, ranging from broad UVB protection to broad UVA protection – and everything in between.
Different types of filters also have particular strengths, says Kateline Turgeon, director of national training at La Roche-Posay and Vichy, explaining that how much protection is offered depends on the amount of the active ingredient in the sunscreen, particle size, photostability and overall product formulation.
Many of the UVB filters have been used in Canada for many years and their efficacy and safety have been well documented, she says. “What consumers should pay special attention to is UVA protection, because there are only a few filters efficacious in that area.”
Only one chemical ingredient, avobenzone, and one mineral ingredient, zinc oxide, offer full UVA protection. Zinc oxide is the only single active ingredient listed in Canada that protects against the full spectrum of UVA and UVB.
Dermatologists regard Mexoryl technology as the best chemical UVA filter, says Ms. Turgeon, adding that Mexoryl SX is a notable photo-stable and water-soluble filter that provides good UVA protection.
Health Canada’s sunscreen monograph now also defines minimum levels for UVA protection, says Ms. Turgeon. In order to qualify for a new UVA logo, sunscreens need a UVA protection that is at least proportional to one third of the UVB protection; they also need to be effective for a critical wavelength of at least 370 nanometres.
“This will also make consumers a little bit more aware that UVA protection has to be taken seriously,” she says, suggesting to check out behindthespf.ca, La Roche-Posay’s new website designed to increase customer awareness.
Dr. Freiman says Canadians are fortunate to have the CDA program, which evaluates sunscreens through independent laboratory testing. “We look at all the data behind the sunscreens. If they meet certain criteria, they get the CDA’s approval and logo.” A list of CDA-approved products is available at www.dermatology.ca/programs-resources/programs/recognized-products.
He adds that it’s important to remember that sunscreen is only effective when it’s used properly. Dermatologists recommend applying sunscreen before going outside, using a generous amount and reapplying it every two hours (or more often if swimming or sweating). Sunscreen is also only one component of a range of sun safety measures. Other strategies include staying out of the sun during peak hours, seeking shade and wearing sun protective clothing and sunglasses.