SPF 101: burning questions answered

SPF 101: burning questions answered

By Maren Stratte and Elizabeth G Stratte, MD

There are a lot of SPFs out there and a lot of questions about what they mean. Here, Dr. Stratte breaks it down for you.


What does SPF mean?

SPF or Sun Protection Factor is a number that explains how well a sunscreen protects you from sunburn.

The number determines how much protection from sun damage you’ll be getting than when you aren’t wearing any sunscreen. NOT HOW MUCH TIME YOU CAN GO WITHOUT REAPPLYING.

For example, wearing SPF 50 means your skin has 50 times more protection than when you aren’t wearing any sunscreen.

What are UVA and UVB rays?

UVA rays (ultraviolet A) cause aging. UVB (ultraviolet B) cause burning. UVB rays cause most skin cancers, but UVA rays definitely contribute. This is why it's important to look for Broad Spectrum sunscreens that filter both UVA and UVB rays.

Physical vs Chemical

Let's break it down...

Chemical SPF:

  • Protects you by absorbing the sun’s rays.
  • Absorbs into the skin.
  • May contain one or more of many possible active ingredients, including oxybenzone or avobenzene. 

Physical SPF:

  • Protects you by deflecting the sun’s rays.
  • Sits on the top of the skin.
  • Contains the active ingredients titanium dioxide and/or zinc oxide.

Physical is loved by people who prefer their skincare to be more natural or “clean”, however Dr. Stratte doesn’t recommend one over the other. It’s up to your preference!


Does sunscreen block Vitamin D?

Studies show it may. This is why it’s important to get Vitamin D from your diet. "I frequently hear from patients that they tan to get their Vitamin D," says Dr. Stratte. "This is doing much more harm than good for your health. Vitamin D can be found in foods like milk, salmon, and even mushrooms. Getting it through your diet is more efficient and protects you from premature aging and skin cancer (a risk of tanning)."

When should I use sunscreen?


The sun emits harmful UV rays year-round. Even on cloudy days, up to 80 percent of the sun’s harmful UV rays can penetrate your skin. Snow, sand, and water increase the need for sunscreen because they reflect the sun’s rays, so even on the slopes it's vital to wear SPF.


Who should wear sunscreen?

EVERY. ONE. There is a sunscreen for every skin type and concern.


How do I apply sunscreen?

It’s important to apply sunscreen to the whole body, using 1 ounce -- or a shot glass full -- of sunscreen to cover the whole body. Do so 15 minutes before going outdoors to allow your skin to absorb the sunscreen. Make sure to reapply every 2 hours, or immediately after swimming or sweating. 

Tip: Make sure to check the expiration date on your sunscreen! A lot of sunburns are caused by using expired solar protection. 


What is water resistant sunscreen?

This refers to how long a sunscreen will stay and remain effective on wet (or sweaty) skin. The sunscreen must undergo extensive testing before it earns the water resistant designation. There are two durations of water resistant SPF-- 40 and 80 minutes. After those designated times, or ideally 15 minutes before the clock runs out, you'll need to reapply to continue the protection.Even if your skin remains dry while using a water resistant sunscreen, you'll need to reapply the sunscreen every 2 hours.

And for the athlete who is tired of their sunscreen running into their eyes, good news! A "Sport" SPF is really just a water and sweat resistant SPF.


What is “Reef Friendly” or “Reef Safe”?

Reef safe sunscreens need to be free of Oxybenzone, Octinoxate, Homosalate, amd Octorcrylene. These ingredients are noted in the research leading to damage of corals, which support ocean life.

This damage includes:

  • Increasing a coral’s susceptibility to bleaching
  • Damaging coral DNA and hormones which interferes with growth and reproduction
  • Causing deformities and growth anomalies

It is vital to make sure you use a reef safe SPF when going to the beach, and non-reef safe sunscreens are actually banned in Hawaii.


Our goal is to make sure every single one of our patients finds an SPF that they love and genuinely WANT to wear every day. Check out our SPF collection to find an SPF for you! Whether it's chemical, physical, tinted, moisturizing, or matting that you're looking for we have it HERE!

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