Tips: Sunscreens should be used to protect the skin and not to prolong sun exposure. They should be “broad spectrum,” that protect against both UVA and UVB. Sunscreens should have a sun protection factor (SPF) of at least 15 and preferably 30. SPF is defined as the least amount of energy needed to produce erythema (primarily UVB) with sunscreen, divided by the least amount of energy needed to produce erythema without sunscreen. Health Canada states that products with a critical wavelength (that at which the sunscreen is still able to block 90% of UVA rays) of at least 370 nm may use the designation “broad spectrum”. The higher the critical wavelength, the greater the UVA protection. Sunscreens with the broad spectrum designation and an SPF ≥15 may use the following statement: “If used as directed with other sun protection measures, decreases the risk of skin cancer and early skin aging caused by the sun”. Sunscreens with an SPF <15 or critical wavelength <370 nm must use the following statement: “This product has been shown only to help prevent sunburn, not skin cancer or early skin aging.”
Water-resistant products may only be labelled as “Water/Sweat Resistant [40 minutes]” or “Water/Sweat Resistant [80 minutes
Commercial products usually contain more than 1 active ingredient in order to provide broader protection and photostability. They should be applied 15 minutes before UV exposure to allow active ingredients to bind to the skin.