To minimize risk of skin cancer sunscreen is only one part of the picture. Hats, protective clothing and avoiding the sun between 10AM and 4PM also help.
To ensure protection against both UVA & UVB rays, look for sunscreen that is labelled “broad spectrum” and contains zinc-oxide, titanium-dioxide or avobenzone. Look for an SPF of at least 30. In the 2007 Consumer Reports analysis to performers were Neutrogena Ultra Sheer Dry-Touch SPF 45 and No-Ad Sunblock Lotion Maximum SPF 45
Apply suscreen 15-30 minutes before sun exposure whenever possible and reapply every 2 hours or sooner if you have been sweating or swimming. Waterproof products will only last for about 1 hour in the water. When you buy sunscreen, write the date on it in indelible pen, throw it away after 2 years.