What is SPF?
The SPF, or Sun Protection Factor, is a numerical ratio based on the time skin would normally take to burn without a sunscreen. For example, if your skin burns in 20 minutes, an SPF of 10 would protect your skin 10 times longer, or for 200 minutes. However, while this might sound like enough protection, most experts recommend that you always use a sunscreen with an SPF 15 or higher.
Sunscreens with higher SPFs may give people a false sense of security, or a license to spend an even longer time out in the sun. A sunscreen should be used to protect your skin from normal sun exposure during the day; it is not meant for you to abuse your skin even more. Remember, studies show sunscreens with high SPF numbers only give minimal extra benefits, but can also cause more irritation to your skin. It is more important to choose a sunscreen that you like and feels good on your skin, rather than choosing a heavy duty SPF 60 product that feels thick and sticky. Regardless of SPF 15 or SPF 60, all sunscreens should be reapplied every 2-3 hours.

What ingredients should I look for in a sunscreen?
When selecting a sunscreen, look for products labeled "broad-spectrum UVA and UVB” protection. The package should include a list of active ingredients. Look for physical sunblocks, such as titanium dioxide or zinc oxide. These ingredients work by actually deflecting sunlight away from your skin, and are much more effective sun protection than chemical sunblocks, such as Avobenzone, octocrylene, and oxybenzone.