8 Questions About Sun Protection

A few weeks ago, several friends and I headed out to lounge in Brooklyn's Prospect Park on a hot, sunny afternoon around 5 p.m. Knowing it wouldn't be too long before the sun started to set, we debated whether or not it was necessary to reapply sunscreen one final time—or if we were safe to go SPF-free in the early evening.

As the default health expert of the group, given my daytime hours spent writing and editing for Health, I was a little embarrassed that I didn't entirely know the answer. So—what else?—I asked a couple of experts, and then tacked on a few extra sunburn, sun protection, and sunscreen questions we could all use definitive answers to.

Can I Still Get a Sunburn After 5 P.M.?

Where there's sunlight, there's the potential for a burn, said Mary L. Stevenson, MD, of the Ronald O. Perelman Department of Dermatology at NYU Langone Health. "It depends on how sensitive you are, but there's definitely still UV radiation occurring if there's still light."

Yes, Dr. Stevenson said, the sun's rays are typically strongest between 10 a.m. and 4 p.m. Yet if you can see the sun, you could get burned, especially if you're fair-skinned and burn easily, Dr. Stevenson said.

Those dangerous hours are determined by how high the sun is in the sky, said Susan Y. Chon, MD, associate professor in the department of dermatology at the University of Texas MD Anderson Cancer Center. But they can vary depending on where you are.

"After 5 p.m. in, say, Seattle, the intensity of the sun might fluctuate with the season, but in Texas, it's still blazing hot and high in the sky," Dr. Chon said. Based on your location, you may be able to safely skip a 5 p.m. sunscreen reapplication—but when in doubt, put on some more.

Can I Get a Sunburn on a Cloudy Day?

I'll admit, I knew the answer to this one already—because I have lived it. I'm sensitive enough to the sun that I've burned on cloudy days and even one winter day while shoveling snow. But Dr. Chon helped me understand why: "The UV still penetrates cloud coverage."

There's a chance cloudy summer days could lead to worse burns, Dr. Chon said. Those gray days tend to feel cooler, so you might be inclined to stay outside longer or forget to reapply sunscreen than on sunnier days when you're so hot, that you seek out shade (or at least remember to lotion up). "People get sunburned all the time on an overcast day," Dr. Chon said.

Even if you don't burn on a cloudy day, UV rays are still potentially damaging and can age your skin, Dr. Stevenson said. So yes, you need sunscreen on cloudy days, on ski trips, on fall hikes—basically all year round.

Can I Get a Sunburn Through a Car or Airplane Window?

I imagine you, like me, tend to assume that when you're inside, you don't need to wear sunscreen. But does a car count? Whoever's sitting on the sunny side for a drive certainly feels warmer. So can UV rays get you, even when you're buckled up?

There's good news and bad news here, and the answer has to do with the two different types of UV rays that experts worry about when it comes to the sun: UVA and UVB. UVB rays are a shorter wavelength and are more closely associated with sunburns and skin cancer risk, Dr. Chon said. The good news is that UVB rays are mostly blocked by the tint of car (or airplane) windows, says the Skin Cancer Foundation

UVA rays may also play a role in skin cancer risk, but they aren't as commonly associated with burns. Instead, they're more likely to add to discoloration and wrinkling of your skin, Dr. Chon said. Here's the bad news: Up to 50 percent of UVA radiation can penetrate this glass and reach your exposed skin, says the Skin Cancer Foundation.

Keep in mind that front windshields aren't tinted for visibility reasons and that the sun may reflect off other cars around you in traffic, sending even more UV rays your way, Dr. Chon added. And let's not forget, if you roll the windows down, you're losing that UVB protection. Driving has been linked to skin cancers on the left side of the body, according to the Skin Cancer Foundation, so be mindful of how often you're hanging that left arm out your driver's side window too.

Is SPF 100 Really Any Better Than SPF 30?

Experts generally recommend using SPF 30 and above with what's called "broad spectrum" protection, meaning it shields you from both UVA and UVB rays.

The higher the number, the smaller the number of UV rays that reach your skin, Dr. Stevenson explained. Yet the number may not be as crucial as you think. "I think focusing on the number after 30 is less important than focusing on using enough sunscreen and reapplying it," Dr. Stevenson said.

That's because most of us aren't using enough—and using a higher SPF might give you a false sense of security that you're set for the day. The American Academy of Dermatology (AAD) reports that most people only use 20% to 50% of the recommended amount of sunscreen.

"We generally say a shot glass–size amount for exposed areas of skin and a teaspoon for your face and neck, then reapply every two hours and make sure you don't miss anywhere," Dr. Stevenson said. "I'm usually shaded under an umbrella and people are still surprised by how frequently I reapply my sunscreen."

If you're using enough, you'll know, because you'll go through a lot of sunscreens. "If one bottle is lasting you the whole summer, you are not putting on enough," Dr. Stevenson said.

Do I Have To Rub in Spray Sunscreen?

Before you roll your eyes in I-can't-be-bothered exasperation, consider this cautionary tale. "I've had patients sunburned in stripes because they spray themselves funny," Dr. Chon said.

Sprays are convenient, sure, but without a post-spray rubdown, you're highly likely to have missed a spot or two, Dr. Chon said. Spray sunscreen formulas are also so fine, that you may easily sweat them off before they have time to sink in, Dr. Chon added.

Both dermatologists actually say they're not huge fans of spray sunscreens because their formulations are usually chemical. Mineral-based sunscreens, on the other hand, create a physical blocker to protect your skin from the sun. "Now, there are some more zinc oxide-based sprays that are better," Dr. Chon said, such as Kiss My Face's Mineral Sun Spray Lotion. Still, "rubbing it in will help," Dr. Chon said.

Can My Eyes Get Sunburned?

Just like your skin can be burned and damaged by UVA and UVB rays, your eyes can too. The result is technically called photokeratitis, a painful eye condition that occurs when your eye is exposed to UV rays from the sun or man-made sources like tanning beds, according to the American Academy of Ophthalmology.

"A wide-brimmed hat is great for skin and also protects your eyes," Dr. Stevenson said. "And sunglasses should have UVA and UVB protection." Luckily, even a lot of the cheap options do, Dr. Chon added.

Can My Lips Get Sunburned?

This is another one I knew the answer to, unfortunately, from my own personal sunburn history. I once sunburned my lips so badly that the swelling made me look like a Kardashian taking a selfie—and not in a cute way. Long story short: You can sunburn your lips, and it's not fun.

It's also dangerous. "It's very common to develop skin cancer on the lower lip," Dr. Chon said. Your mouth's anatomy simply isn't helping you here: The sun hits your lower lip because of the way it sticks out from your face, Dr. Chon explained. Be liberal with your sun-protective lip balm—the AAD recommends using at least SPF 30.

Does Getting a Base Tan Prevent Me From Burning Later?

At the end of a long, cold winter, I always feel like my skin is nearly translucent. Surely a little color must be protective to the areas that haven't seen the sun in months, right? Turns out, the idea that you need a base tan to avoid future sunburns is a big misconception, Dr. Chon said.

"The base tan is your first sun damage of the summer," Dr. Chon said. "Just because you have some color doesn't mean you cannot also sunburn on top of a tan, which happens all the time."

A Quick Review

Everyone needs sunscreen to minimize short-term and long-term damage to the skin from the sun's rays. Besides seeking shade and wearing protective clothing and sunglasses, using sunscreen is an important habit to reduce your risk of skin cancer. Always follow the best practices from experts to keep your skin healthy.