Long days and strong rays mean it's time to upgrade your basic daily sunscreen habit to a full-on slather. We all know that using sunscreen helps to prevent sunburns and skin damage, but we're stumped when it comes to the gibberish slew of letters and numbers on the label. Read on to learn what nine common sunscreen terms mean.

1. SPF: SUN PROTECTION FACTOR

SPF tells you how much much UVB light (more on this in a bit) is filtered out, so it’s often used as a proxy for how long you can stay in the sun without doing damage (to an extent). But the FDA cautions that SPF shouldn’t be thought of in that way, as there are so many variables that go into solar radiation. Instead, they suggest using SPF as a comparison: A higher SPF provides more protection than a lower SPF. According to Jeremy A. Brauer, a board certified Manhattan dermatologist, “SPF 30 blocks 97 percent of UVB rays, SPF 50 blocks 98 percent.” Keep in mind that no sunscreen can block 100 percent of UVB rays.

2. UVA: ULTRAVIOLET A

UVA radiation is one type of light that causes skin aging and skin cancer. According to Adam Friedman, Associate Professor of Dermatology at the GW School of Medicine and Health Sciences, UVA light "does not burn, but is sneaky and penetrates deeper than UVB, accelerating the aging of your skin and causing skin cancer." UVA rays also contribute the most to our UV exposure.

3. UVB: ULTRAVIOLET B

UVB light causes sunburns and is more intense than UVA. These rays contribute less to our overall UV exposure than UVA rays do, but have serious, immediate effects on the topmost layers of skin.

4. BROAD SPECTRUM UVA/UVB

The term broad spectrum means that the sunscreen protects against both UVA and UVB light—all sunscreens block UVB (temporarily), but some let UVA slip though. It’s one of the most important markers to look for because both types of light can cause skin cancer.

5. PHYSICAL/MINERAL SUNSCREEN

Sunscreen formulas can be physical, chemical, or a combination of both. Physical sunscreens act as a literal barrier: They block the light from reaching your skin, reflecting the UV radiation outwards.

6. CHEMICAL SUNSCREEN

A chemical sunscreen works in a different way: It absorbs, rather than blocks, the light. When the radiation is absorbed by the sunscreen, it’s converted to heat that is then released by your skin. Friedman says that the problem with chemical sunscreen is “each time they do their thing, a percentage of the filter stops working. So ultimately over time, it can't change that UV energy into harmless warmth.”

7. WATER RESISTANT

You’ll never see an FDA-approved sunscreen that is "waterproof," or sweatproof for that matter. Instead, the FDA requires the label to note how long the product can last in water. You’ll see this on the bottle written as “water resistant, 40 minutes,” for example. This means that after 40 minutes of wear, the sunscreen will need to be reapplied because it won’t work as well—even if you haven't been in the water.

8. SPORT

The FDA doesn’t regulate the use of words like “sport” when it comes to sunscreen. This is a marketing term used to make the product more appealing to active people. If you're interested in a sunscreen with staying power, pay more attention to the SPF and water resistance.

9. PA+ RATING

If you pick up a bottle of sunscreen while on vacation or order it online, you might be confronted with "PA" followed by some plus signs instead of the familiar SPF. The PA rating system, common in Japan and South Korea, tells you how well the sunscreen protects from UVA rays, instead of UVB. The more plus signs that follow PA, the better. PA ++++ offers the most UVA protection, PA + the least.