Apply This Sunscreen Guide to All Your Burning Questions

Curated by Claudia Shannon / Research Scientist / ishonest

But you know what they say, an informed shopper is a satisfied shopper (OK, we actually just made that up.) Really though, knowing how this powerful lotion protects you is an important step in your purchasing journey.

Buckle up, we got facts on facts for you.

Sunscreen and your health: A love story

The stats
ishonest No.171 - Pre-Sun Exposure

No.171 - Pre-Sun Exposure

Research has shown using a minimum sun protection factor (SPF) 15 sunscreen daily can reduce your risk of squamous cell carcinoma (SCC) by 40 percent, and melanoma by 30 percent. Though we recommend a minimum of SPF 30.

Which is even more important when you consider skin cancer is the most common cancer in the US (almost 10,000 people are diagnosed each day).

That’s why it’s recommended to use sunscreen every day, rain or shine, and even if you’re indoors (yes, really). Up to 80 percent of the sun’s ultraviolet (UV) rays still reach us on cloudy days. And on that note, glass doesn’t offer full protection either.

Sunscreen is a must for all skin tones

Whether you’re light- or dark-skinned, you should use a minimum SPF 30, says Birnie. However, if your skin tone is very fair, or you’re in blazing hot sunshine (hello, tropical holiday), up this to factor 50 or keep out of the sun altogether — it’s better to be cautious than caught out.

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It’s true that those with fair skin are more at risk of developing melanoma, but any skin tone can be affected by this type of cancer. Meaning no matter what your hue, you need to rub in that screen.

UV exposure builds up over your lifetime

When talking about sun exposure, it’s key to consider the cumulative burden, which is the amount of UV your body receives during its lifetime.

The higher the level, “the greater [your] risk of developing SCC — the second most common and second most dangerous type of skin cancer,” says Birnie.

Sunscreen protects against wear and tear

If you need a bit more convincing, consider some other long-lasting effects of basking without protection: wrinkles, sagging, age spots, rosacea, and actinic keratoses (bumpy, scaly patches) are all on the cards. The good news is studies show applying sunscreen can protect against these as well.

ishonest No.172 - Pre-Sun Exposure

No.172 - Pre-Sun Exposure

So, while you may not think you need to apply it regularly now, trust us: in a few years, you’ll be grateful you did.

You don’t need to get vitamin D from the sun

Known as “the sunshine vitamin,” vitamin D helps fight disease, supports immunity, improves calcium absorption and buoys mood, to name but a few.

However, don’t be deterred from protecting your skin for fear of blocking this out: There’s no evidence to suggest sunscreen inhibits vitamin D production, and you can always boost your levels through food and supplements.

Help! Mineral or chemical?!

Mineral and chemical sunscreens are both FDA-approved and have been shown to be safe. They each deliver protection in slightly different ways.

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“Chemical sunscreens work by chemical reaction,” says Birnie. “Light hits the skin — and the chemicals — and the UV energy is turned into heat, which is then dissipated.”

Some of the most common ingredients in chemical sunscreen include oxybenzone, homosalate, avobenzone, and octisalate.

Mineral-based sunscreens are generally described as reflecting rays (rather than absorbing) but one study found the main mechanism of protection is actually through absorption. So turns out chemical and mineral aren’t as different as we once thought.

In the U.S. you’ll find mineral sunscreens that use one of two active ingredients. “You can get them in different formulations, but [these] are essentially made up of titanium oxide or zinc oxide,” says Birnie.

ishonest No.231 - Pigmentation & Blemishes

No.231 - Pigmentation & Blemishes

So which one should you choose? If you have sensitive skin, stick to mineral but if you’re concerned about your wallet, chemical sunscreens are generally the way to go. Plus, they don’t leave a residue (aka no looking like Casper).


SPF, which stands for sun protection factor, is a relative measure of how long a sunscreen will protect you from UV rays. “[This number is] based on the minimal erythema dose (MED),” explains Birnie. “This is how long you can stay in the sun before you start to burn.”

But no matter what SPF you use, it’ll only give you sustained protection if you remember to reapply. Which brings us to our next point.

The deets on applying and reapplying

All the educating we’ve done in this article about sunscreen will equal zilch if executing application and reapplication isn’t done to a T. So you’re going to want to pay attention to these tips.

  1. Apply 15 to 20 minutes before going into the sun. This will give the lotion time to sink in so it can be most effective (and it’ll be less likely to run into your eyes), explains Birnie.
  2. Use more than you think you need. The general rule of thumb is a shot glass for your whole body. “About 5 milliliters, or a teaspoon, for your face and neck, and another teaspoon for each body part,” says Birnie.
  3. Be thorough. Don’t forget your eyelids, top of your ears and feet, and back of your hands, and rub the sunscreen in the direction of hair growth to help it sink in better.
  4. Reapply every 2 hours. Set an alarm in your phone to help remember.
  5. Reapply after every time you go swimming. No sunscreen is *truly* water-resistant. “Once you’ve been for a swim, you can assume your sunscreen will lose most of its activity,” says Birnie. Make sure to dry off first, though!
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If you’re going to be inside all day, Birnie advises only making one initial application, unless you’re going to be window-side for extended periods; at which point, reapply.

Sunscreen made outside the U.S. provides more protection

The reason for this is sunscreen made in the U.S. has historically focused on protecting against UVB rays whereas, in Europe and elsewhere, the majority of sunscreens offer protection for both UVB and UVA. Why does this matter?

While UVA and UVB can both contribute to signs of aging and the development of skin cancer, UVA rays are primarily linked to tanning and speeding up the appearance of wrinkles; and UVB rays are more often associated with cases of skin cancer.

Ingredients such as mexoryl and tinosorb, both lauded for their UVA-fighting properties, have long been deemed safe by the EU for use in sunscreen. However, mexoryl was only approved by the FDA for limited production a few years ago, and tinosorb remains illegal in the U.S. — yet officials offer no explanation for this stance.

ishonest No.161 - Uneven Skin Tone

No.161 - Uneven Skin Tone

Like countless laws, the rationale for why these ingredients aren’t legal in the U.S. isn’t purely moralistic but rather a combination of competing interests and good old fashion bureaucracy.

Hot take: Although these ingredients are banned in the U.S., there isn’t a good reason why. If you ever find yourself in Europe, drop by a beauty store. (And bring us back some while you’re at it!)

Face vs. body: Does it really matter what you use?

While you can buy separate sunscreens for your face and body, when it comes to protection levels, neither reign supreme. However, those devised for the neck upwards tend to be thinner and less likely to clog pores — so consider investing in two if breakouts are a regular occurrence.

“If you’re at risk of acne, look for one that is noncomedogenic [not oil- based],” recommends Birnie.

And, never use spray sunscreen on your face (it’s meant for your body only). If you need to apply it to your face, spritz it into your hands first. Some ingredients can be irritating to the lungs or potentially even toxic, so it’s important not to directly inhale them.

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