Dr. Anatoli Freiman publishes a review of sunscreens and sun protection in the Summer 2013 inaugural dermatology issue put out by the Globe & Mail and the Canadian Dermatology Association, click here to view. Dr. Freiman emphasizes that skin cancer is the most common type of cancer – one in six Canadians will develop skin cancer in their lifetime. It is also one of the most preventable. The primary environmental cause of premature skin aging and most skin cancers is ultraviolet (UV) radiation from sun exposure. UV radiation is composed of three wavelengths: UVA, UVB and UVC, out of which UVA (320-400nm) and UVB (290-320nm) rays are specifically carcinogenic. Sunscreens work by absorbing or reflecting UV radiation. Sunscreens are generally divided into two types: organic/chemical preparations which absorb UV radiation, or inorganic/physical preparations, such as titanium dioxide or zinc oxide, which physically block UV radiation. Many products combine chemical and physical ingredients, and sunscreens come in a variety of forms, such as lotions, gels and sprays.
There are some key features of sunscreens that are important to understand:
• SPF stands for Sun Protection Factor and indicates sunscreen effectiveness against UVB rays. There is an incremental protection with higher SPF, and dermatologists typically recommend using a sunscreen with an SPF of at least 30 which blocks 97% of UVB. SPF does not indicate UVA protection nor that the sunscreen is broad-spectrum.
• Sunscreens labelled as broad-spectrum offer protection against both UVA and UVB rays and thus should be optimally used. Critical wavelength of at least 370nm is a laboratory measure of broad-spectrum protection.
• Photostability of sunscreens refers to their stability upon exposure to sunlight.
• Water resistant sunscreens maintain SPF protection level after 40 or 80 minutes of water immersion as determined by testing.
• Sunscreens should ideally be non-comedogenic (won’t block pores), non-irritating, hypoallergenic, and minimally or non-perfumed.
Dermatologists recommend that broad-spectrum (UVB & UVA protection) and high SPF (30+) sunscreen should be generously and evenly applied to the skin 15 minutes prior to sun exposure. It should also be reapplied in sufficient quantities every two hours or more frequently if swimming or sweating. Of note, 30ml (approximately an ounce or a shot glass) of sunscreen is needed to adequately cover the body skin surface and a teaspoon is needed for the face. Sunscreens are advocated for kids over the age of 6 months, while other sun protective measures should be employed in younger infants. In general, it’s important to keep in mind that sunscreen use is just one of the important measures of overall sun safety. Other main strategies include staying out of the sun in peak hours (e.g. 10am-3pm), seeking shade, and wearing sun protective clothing and sunglasses.