Everything you want to know about sunscreen

From safety and effectiveness to who should use sunscreen and how to apply it, Canadian dermatologists review the latest evidence and guidelines on use of sunscreen.

The review, published in CMAJ (Canadian Medical Association Journal), recommends that everyone older than six months of age should use sunscreen to protect against skin cancer.

Most skin cancers develop because of long-term sun exposure. Sunscreen reduces the risk of developing skin cancer by blocking solar radiation through chemical or physical sunscreen filters such as titanium dioxide and zinc oxide.

"Exposure to ultraviolet radiation is directly harmful and has been associated with the development of skin cancers, which are common in Canada. High-quality evidence has shown that sunscreen reduces the risk of developing both melanoma and nonmelanoma skin cancer," writes Dr. Megan Sander, a dermatologist and clinical lecturer at the Cumming School of Medicine, University of Calgary, Calgary, Alberta, with coauthors.

Some key points:

• Prevention—Evidence from randomized controlled trials indicates that sunscreen is effective at protecting against skin cancer as well as premature aging of the skin.
• Non-White populations—There is a lack of evidence for the effectiveness of sunscreen in people with darker skin. Current evidence is mostly limited to White people, who have a higher rate of skin cancers.
• Babies—Sun avoidance and protective clothing are recommended for babies. Sunscreen is not recommended for use before age 6 months because of the potential for systemic absorption of sunscreen ingredients.
• SPF—Sunscreens with an SPF (sun protection factor) of 30 or higher are recommended in cream or lotion format. Spray-on sunscreens are not recommended as they can be dispersed, are flammable and their effects if inhaled are unknown.
• Harms—Some people can have skin reactions such as contact dermatitis, especially to chemical sunscreens, and there is evidence these sunscreens can be systemically absorbed, although the clinical importance of the absorption is not known.
• Environmental impact—Recent evidence indicates that chemical sunscreens can be detected in water and fish and may contribute to the bleaching of coral reefs.

"Sunscreen is only one part of a comprehensive photoprotection strategy. It is important to counsel patients regarding behaviours for avoiding ultraviolet radiation, including the use of wide-brimmed hats, eye protection (e.g., "wrap-around" sunglasses with ultraviolet radiation protection) and seeking shade when the ultraviolet index is above 3 (usually 11 am-3 pm, April to September in Canada)," write the authors.

Research into the safety of sunscreens and of new technologies continues.