You already know that too much sun can be deadly – but how much do you really know about sunscreen? Here are four facts that you need to know.

1. Know Your A’s and B’s

The FDA now classifies sunscreens two ways: 1) sunscreens that help prevent skin cancer, skin aging and sunburn (ultraviolet A) and 2) sunscreens that only protect against sunburn (ultraviolet B).

Dermatologists across the Sutter Health network recommend using an SPF of 30 or higher for the best protection – especially for people with sun sensitive conditions like lupus or those taking oral medications that make skin more sensitive to the sun.

Sutter Health experts say selecting a sunscreen with an SPF of 30 will protect you against about 97 percent of ultraviolet B rays. However, if you want to cover your bases and get the best protection, dermatologists recommend looking for the term, “broad spectrum,” which also blocks ultraviolet A.

How well does your SPF filter the sun’s harmful rays?
SPF 2 blocks about 50 percent of UVB rays.
SPF 10 blocks about 85 percent of UVB rays
SPF 15 blocks about 95 percent of UVB rays.
SPF 30 blocks about 97 percent of UVB rays.

An SPF higher than 30 doesn’t provide any additional UVB protection, it only allows you to spend a longer time in the sun without burning.

2. There is no such thing as a truly waterproof sunscreen

You should reapply sunscreen at least every two hours and even more often if you’ve been swimming or sweating.

3. Apply liberally and early

You should apply about one ounce of sunscreen per body part – enough to fill a small shot glass – at least 15 to 20 minutes before sun exposure. It needs time to spread over and into your skin.

4. Altitude increases the sun’s potency

For every 1,000-foot increase in altitude, the sun’s potency increases.

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