Your guide to SPF and wearing sunscreen the right way

Summers come and go, but many people still don’t know how to wear sunscreen correctly.

This fact is especially concerning since these ultraviolet ray-shielding topical can help prevent skin cancer, which is the “most commonly diagnosed skin cancer” in the country, according to the U.S. Department of Health and Human Services.

The health agency reports that approximately five million Americans get treated for skin cancer each year.

If you need a refresher on how you’re supposed to wear sunscreen, here’s a quick guide on what SPF is and how it works, the differences between sunscreen types and which sunscreens are better for your face and body.

Sun Protection Factor – commonly known as SPF – is the measure of how much UV radiation is needed to produce sunburn on protected skin compared to unprotected skin, according to the FDA.

With sunscreens, the SPF rating scale indicates the level of sunburn protection a person can receive – if applied correctly.

“As the SPF value increases, sunburn protection increases,” the Food and Drug Administration (FDA) says. “[But,] SPF is not directly related to time of solar exposure but to amount of solar exposure.”

The FDA recommends 2 milligrams of sunscreen for every square centimeter of exposed skin.

The amount of UV radiation that comes down from the sun varies throughout the day, so an hour of sun exposure at 9 a.m. could be equivalent to 15 minutes of sun exposure at 1 p.m. 

How is this possible? Well, the sun’s rays are at their strongest between 10 a.m. and 4 p.m., according to the United States Environmental Protection Agency. 

This means people who go outside during the 18 other hours of the day are exposed to a lower amount of UV radiation, but health experts universally agree that sunscreen should be worn for added protection.

How do I find the right amount of SPF?

Per the FDA’s sunscreen testing, the agency recommends 2 milligrams of sunscreen for every square centimeter of exposed skin. 

A mother applies sunscreen to her child's face.
Sun Protection Factor – or SPF – is the measure of how much UV radiation is needed to produce sunburn on protected skin compared to unprotected skin.

The FDA also recommends applying sunscreen 15 minutes before going out and reapplying the product at least every two hours. Water-resistant sunscreens should be used if a person decides to go swimming or will do an activity that’ll cause profuse sweating. Reapplication should be done on dry skin at least every two hours.

While the FDA is clear about how much sunscreen should be used for maximum protection, few people apparently wear their sunscreen at the recommended amount – if at all.

“Generally, there has to be a balance because what happens is that we do know that the average public, including ourselves, when we put on the sunscreen, we don’t put on that two-milligram-per-centimeter-square, which is the one that is used for testing purposes mandated by the FDA,” said Dr. Henry Lim of Henry Ford Health – a not-for-profit health care organization in Detroit.

“So automatically, the end-use SPF is going to be lower than the labeled SPF because of the inadequate application as compared to the amount that is used for testing,” Lim continued.

He said dermatologists typically recommend SPF 30 as a starting point. If used correctly, the SPF rating would filter out 97% of UVB rays – the wavelength that’s associated with skin burning, which is 4% higher than the amount SPF 15 filters out. 

But, again, since most people may not wear sunscreen at the recommended amount, a slightly higher SPF “would compensate for under-application while still providing relatively good protection,” according to Lim.

A woman's back is shown to be peeling from sunburn.
UVB rays are the wavelength that’s associated with skin burning.

For people who are going to be exposed to the sun for a long period of time, Lim said they can choose a sunscreen that is at least SPF 50.

What about UVA and visible light?

While UVB is associated with skin burning, UVA is associated with skin aging. Both forms of UV contribute to skin cancer risks, according to the U.S. Centers for Disease Control and Prevention.

Broad-spectrum sunscreens are formulated to protect people from harmful UVA and UVB rays. A label denoting a sunscreen’s broad spectrum capability should be present on the product’s packaging, according to Lim.

Aside from UV rays, there’s visible light, which can cause erythema – superficial reddening of the skin – and tanning in people who have dark skin, according to a Photochemical & Photobiological Sciences study in the National Library of Medicine.

A woman's cheek has intense freckling from dangerous sun exposure.
Even those with darker skin can suffer from the effects of sun exposure, dermatologists warn.

“If one were to protect against the visible light, which I think is important for darker skin individuals, then tinted sunscreen would be the one to use because we know that visible light can cause very significant tanning and long-lasting tanning on the skin,” Lim told Fox News Digital. 

“So, we want to minimize that effect to prevent the blemishes,” he continued. “That could be darkened with sun exposure.”

How do I measure out sunscreen like a pro?

Applying two milligrams of sunscreen to each square centimeter of skin can be a tricky task. This is especially true for Americans who aren’t familiar with the metric unit of measurement in their daily lives.

Luckily, dermatologists have come up with an easier sunscreen measurement system called the “rule of nines” – and it uses teaspoons in place of milligrams.

“It is essentially one teaspoon for the face, head and neck. One teaspoon for the forearm and arm, each. So, one teaspoon for left, one teaspoon for right,” Lim told Fox News Digital. “And two teaspoons for the [torso’s] front and back and then two teaspoons for the left leg and two teaspoons for the right leg. So, it’s nine teaspoons total.”

“That translates to about one ounce or one shot glass of sunscreen,” Lim continued. “Most individuals do not use that much. Usually, most individuals who have been studied over and over use about 0.8- to 1-milligram per centimeter square. So, it’s actually one-half of what the FDA recommends.”

Which are the best sunscreen types for the face vs. body?

Commercially manufactured sunscreens generally fall into the lotion, cream, gel, oil or spray categories. Each can be used on the body, but lotions, creams, oils and gels are better suited for the face because aerosol products can be irritating to the eyes, nose and lungs, experts warn.

A woman sprays sunscreen on a man's back.
About 50% of the sunscreens that are now sold in the US are in spray form, according to one doctor.

Even still, spray sunscreens are popular among consumers and can be found in most stores.

“About 50% of the sunscreens that are now sold in the US are in spray form,” said Dr. Darrell Rigel, clinical professor at the Mount Sinai Icahn School of Medicine in New York City.

“Sprays are good and bad. Sprays are good in that you get to cover a lot of areas very quickly, but sprays are bad in that a lot of times you don’t know what you’ve missed,” Rigel continued. “I tell people honestly, spray a full coat on and then spray a second coat on and let’s hope you don’t miss the same place twice.”

Do you actually need a different sunscreen for your face? 

While almost any sunscreen use on the face is better than going without sunscreen, some textures and formulations might feel better than others.

A woman applies sunscreen to her face.
Doctors recommend using lighter sunscreens on your face, as opposed to greasier textures.

“The vehicle, what the sunscreen is put in to deliver it, that makes a difference for face and body,” Rigel told Fox News Digital. “You wouldn’t want something really greasy on your face, right? Because it can make you break out. You want something lighter on your face, just like when you’re looking for a moisturizer or something.” 

“Your body wants something a little more substantial,” Rigel continued. “What’s really more important than the greasiness or thinness of it is what’s called substantivity, which is, how long does the sunscreen last before it breaks down and has to be applied. And typically, the heavier sunscreens tend to last a little longer.” 

However, there isn’t much of a difference between face and body sunscreens, Rigel said. The cosmetics industry makes more of a distinction than there really is.

Is there a “right” SPF number for face sunscreen?

Due to the fact that most people under-apply sunscreen, Rigel told Fox News Digital that he recommends a higher SPF for the face.

“With people using 25% to 50% of the rated amount that they apply, you’re only going to get 25% to 50% of the SPF protection that’s on the label,” Rigel said. “So, the real advantage of a higher SPF is that they’re more forgiving in real-world situations.”

“In general, I tell people to use a minimum of SPF 50 because they under-apply, if they put 25% on they’re going to get SPF 12, if they put on 50% they’re going to get SPF 25,” Rigel continued. 

“One-third of all skin cancers of the entire body occur on the nose. Everybody’s nose sticks out and catches the sun over a lifetime. So, therefore, I tend to recommend a little stronger amount on the face that’s chronically exposed.”

Other areas where skin cancer is commonly found include the lips, ears and scalp, and this usually happens “because they’re not normally protected,” Rigel said.

Sunscreen is squeezed out of its tube into a question mark shape.
Rigel recommends using stronger SPFs on the face than the rest of the body.

What about sunscreens for people with sensitive skin or skin conditions? 

People who have sensitive skin or a skin condition usually benefit from choosing a sunscreen that’s in harmony with their skin. Certain textures work better with certain skin types.

“It goes back to the formulation,” said Rigel. “If you have acne, you don’t want to apply something that’s very greasy to your face. So, there are gels, which are alcohol-based, that will not be as greasy for that, and they’re also not going to cause acne.”

He continued, “What I tell patients in general, if you’re putting on a sunscreen that’s leaving an oil slick behind you in the water, then it’s probably too heavy for you.”

“If you have eczema or psoriasis, you probably wouldn’t want something that’s too drying,” Rigel said. “So, you might not want the gel, you might want the cream or the lotion or something that’s better.”

A group of young people run into the ocean.
Inorganic sunscreens work by absorbing ultraviolet radiation and converting it to harmless red light.

What ingredients should you look out for?

Sunscreens fall into two classes, according to Rigel: organic and inorganic.

“The organic sunscreens are the ones we typically think of – that oxybenzone and the octinoxate and all the other things that are in that in a traditional sunscreen,” he explained. “The advantage of those is they tend to be clear, and they are less obvious on the skin. They get absorbed in the upper layer of the skin, so they’re a bit more waterresistant when you’re in the pool.”

“The inorganic sunscreens are the zinc oxides or the titanium dioxides,” Rigel continued. “Those are more like a coating on the skin, and they reflect the sun’s ultraviolet rays, as opposed to the organic sunscreens.”

He added that inorganic sunscreens work by absorbing ultraviolet radiation and converting it to harmless red light, which isn’t visible to the naked eye in a bright room. 

“That’s what [inorganic sunscreens] do,” Rigel said. “They take you from a dangerous wavelength to a non-dangerous wavelength.”

“The best sunscreens have a little of both in them,” he noted. “They give you the advantage of the reflection, and they also have water resistance.”

How to prevent sunscreen white cast? 

If you’re not a fan of sunscreen because it leaves a white film on your skin, you’re not alone. 

“This is a real issue, especially if you’re a darker-skinned individual,” Rigel said. “To use the zinc or titanium, you’re going to have like a whitish sheet on your face.”

A woman shows sunscreen she has pumped into her hand.
Darker-skinned people are more likely to be left with a white film on their face after applying sunscreen.

If this is a sunscreen woe that ails you, Rigel recommends sunscreens that have iron oxide, which is a common mineral that’s used in cosmetic manufacturing for its darker pigment.

“What I tell people is try the sunscreen on the back of your hand and see how you like the feel of it, how you like the look of it. Is it fine?” Rigel said. “If you like it, and it matches, then you could put it on the other areas that are exposed to see how you do.”

He noted that while a person’s hands will likely be a different tone from their face, it’s still fairly close because both areas have received sun exposure over the years.

“It’s the best way to get a feel for what’s good, what’s not and what’s going to work for you,” he said in reference to the technique.

“The best sunscreen, in general, is the one you’re going to use,” Rigel added. “It’s no good when it’s in the bottle. That’s why the cosmetic acceptability is very important, too.”

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