How much do you know about sun safety? These facts will help ensure your skin is well-protected:

1. The sun emits two types of rays that reach your skin, UVA and UVB. What’s the difference between the two?
Ultraviolet A (UVA) rays emit the same amount of radiation from sunrise to sunset, 365 days a year. Ultraviolet B (UVB) rays are stronger in the summer, especially between 10 a.m. and 4 p.m.

2. Are UVA and UVB rays equally harmful to skin?
Yes, but they affect it in different ways. UVB rays are responsible for sunburn and skin redness. (Think “B” for “burning.”) They cause inflammation, surface dryness and excess dry skin buildup.

UVA rays are weaker than UVB rays but pass further into your skin. They stimulate excess pigment, resulting in dark marks, age spots and dullness. UVAs also break down collagen and elastin, causing lines, wrinkles and sagging. UVA rays can penetrate glass, which means they harm your skin even while indoors.

3. What does SPF stand for, and how does it work?
SPF is short for “Sun Protection Factor.” The higher the SPF, the more protection. But exactly how long a sunscreen protects you depends on your skin color and its tolerance to UVB rays.

To get a sense of how long you can stay in the sun, multiply your sunscreen’s SPF number by the amount of time it takes your skin to burn in the sun.

If your skin turns red in 10 minutes without sun protection, your math would look like this:

• SPF 15 x 10 minutes = 150 minutes (2 ½ hours) without getting burned
• SPF 30 x 10 minutes = 300 minutes (5 hours) without getting burned

…but there’s a little more to it than this. First, no sunscreen can block out 100% of the sun’s rays. Since you can’t rely on sunscreen for complete protection, be sure to cover up your body and wear a big hat and sunglasses.

4. What’s the difference between physical sunscreen and chemical sunscreen?
The two types of sunscreens protect skin in different ways and have different properties. Physical sunscreens, such as zinc oxide, reflect and scatter light and are gentle on skin — which is why Rodan + Fields UNBLEMISH and SOOTHE sunscreens are physical sunscreens. Chemical screens, such as avobenzone, absorb light and blend well with more ingredients. Rodan + Fields REVERSE, REDEFINE and ESSENTIALS sunscreens are chemical sunscreens.

Whether physical or chemical, all Rodan + Fields broad-spectrum sunscreens are formulated to protect against damage from both UVA and UVB rays.

5. How much sunscreen do I need?
More than you probably think! Apply one tablespoon of sunscreen to your face and one ounce — the amount that would fill a shot glass — to your body for adequate sun protection.

6. How frequently should I reapply sunscreen?
One application of sunscreen won’t protect your skin for the entire day. You should reapply sunscreen every two hours — more frequently if you’ve been in the water. This is true even if you’re using a sunscreen with a high SPF.

Now that you’re armed with sun-care knowledge, forward this post to a friend.