Standard Sunscreen Recommendations Ignore People With Larger Bodies
Chloe Rosey
There are few feelings I love more than the sun on my bare skin in the summer. But I also know that the UV rays that give me a wonderful dopamine rush can do a lot of damage–both medical (skin cancer) and cosmetic (fine lines, dark spots, etc.). So when it comes to sunscreen, I tend to slather it on thick. I’d guess that I usually err on the side of using too much, and my SPF obsession has even become a bit of a running joke among my friends.
Still, despite my best efforts, I’m not immune to the occasional sunburn. It’s hard to get sunscreen application just right, and I’ve sometimes wondered if my proclivity for overdoing it could actually be a symptom of an underlying uncertainty around how much I, especially as a fat person, really need to properly protect my skin.
So how much sunscreen should a larger person actually use?
Turns out, no one really knows! The American Academy of Dermatology (AAD) says that “most adults” need about one ounce of sunscreen—or enough to fill a shot glass (about two tablespoons)—to “fully cover their body.” But who are “most adults”? Statistically speaking, the majority of adults (around 74%) in the United States are “overweight,” or at least considered so based on the body mass index (BMI), a widely used but deeply flawed measure of health. Yet by and large, the medical community treats fat people like the exception, leaving us underrepresented in many clinical trials and studies and often building recommendations around folks with a “normal” weight, even though they are, in fact, the minority.
“Most things in medicine are based on the average male size,” Mona Gohara, MD, an associate clinical professor of dermatology at the Yale School of Medicine, tells SELF. “In medical school, we would learn about the 70-kilo man, which is like, you know, 150 pounds or whatever. We’re not serving a lot of our patients.” Dr. Gohara is talking about the “Reference Man,” a concept that was developed in 1974 by the International Commission on Radiological Protection to help standardize radiation exposure estimates. This fictional dude weighs 70 kilograms (154 pounds) and is five-feet-seven-inches tall.
Both Dr. Gohara and Susan Massick, MD, a board-certified dermatologist at The Ohio State University Wexner Medical Center, agreed with my logic that people who are, say, fat or tall, will inherently have more surface area that needs to be coated in sunscreen. But neither knew of a visualization tool similar to the shot glass analogy that’s inclusive of people with larger bodies—because, again, those of us outside of the “norm” are largely left out of standard application guidance from major dermatology organizations, like the AAD and the Skin Cancer Foundation.
Since sunscreen guidelines for larger people don’t exist, I used math to create my own.
After much digging (googling), I still couldn’t find official recommendations on the ideal amount for different body sizes. But one formula kept coming up in my research: two milligrams per square centimeter. This is the amount of sunscreen the Skin Cancer Foundation recommends (the FDA also uses it to test and confirm that the actual SPF of a product matches what’s on its label). And while this formula is technically size-inclusive, it’s not very helpful in real life—when you’re trying to figure out how much to squeeze out of your bottle or tube.
But as I continued to mull over the question of how much sunscreen larger people might need, it dawned on me that I could use math to find an answer! Heads-up: We believe in showing our work—which we had a mathematician check, FYI—so we’re about to take you back to high school algebra class. If you’d rather not revisit those days, just scroll to the chart below (or simply click here to jump down to it).
Okay, let’s get nerdy: If we know that sunscreen should be dosed at 2 mg per cm² and the standard recommendation for “most adults” is one ounce, we can create a formula to find out how much surface area that ounce of sunscreen would cover if applied at the suggested dosage. So that’s what I did: I used the equation 2 mg(X cm²) = 1 fl oz, converted that ounce into milligrams (1 fl oz = 29,573.53 mg, making my equation 2 mg(X cm²) = 29,573.53 mg), solved for the surface area (X), and found that one ounce would cover 14,786.77 square centimeters of skin, or 1.48 square meters (all numbers are rounded to two decimal places for simplicity).
The next step was to plug the weight and height of the Reference Man into a body surface area equation (I used the popular DuBois-DuBois formula via this calculator), which told me that his total body surface area would be 1.81 square meters. That means that one ounce of sunscreen would cover about 81.72% of his skin (when you divide 1.48 by 1.81, you get 81.72%). That tracks with the AAD’s recommendation for “most adults” if you consider that unless you’re at a nude beach some areas of your body won’t need to be slathered in SPF.
To get accurate sunscreen guidelines (based on the two milligrams per square centimeter rule) for different body sizes, all you have to do (lol) is use a body surface area formula (again, like the DuBois-Dubois) with different height and weight combinations. Then, you take 81.72% of each answer, and plug those numbers back into the 2mg(cm²) = 29,573.53 mg equation I created to get the recommended amounts.
Or don’t if you don’t want to: I did the math for you and put together a chart with different heights and weights, along with their respective sunscreen dosages. This may give you a rough idea of the quantity of sunscreen you need to cover (most of) your body.
Size-Inclusive Sunscreen Guide
The chart above is a very rough estimation and assumes that about 80% of your skin will require sunscreen coverage. Depending on what you’re wearing, that may mean you need more or less than the chart suggests.
The method I came up with is far from perfect, though—and it shouldn’t have been on me to figure it out in the first place.
As excited as I was to work out a reliable way to calculate sunscreen dosages for different body sizes, I acknowledge that this method is certainly flawed. The body surface area formula is an imperfect approximation, and, like the BMI, only uses height and weight in its calculation, ignoring other factors (like body shape) that might affect a person’s actual skin surface area. Also, a lot of people prefer not to know how much they weigh (histories of disordered eating and weight stigma can make that number feel triggering and fraught).
All of that said, we’re working with what we’ve got here. And while we don’t have a perfect science, or inclusive recommendations that are also practical from a trusted institution, doing the math does give us a way to apply the AAD’s standard one-ounce advice to a much wider range of people.
At the same time, I recognize that it’s not the simplest approach, so in the case that working with the numbers isn’t your thing, I asked Dr. Gohara and Dr. Massick for some additional tips and tricks to ensure you’re properly protected.
A few easier ways to ensure you’re using enough sunscreen, regardless of your body size
More is probably better.
Research suggests—and the experts I spoke with agree—that most people don’t even apply the one-ounce recommendation, so be like me and err on the side of more. “The idea that dermatologists want to emphasize is that a lot of folks just don’t use enough,” Dr. Massick says.
For your face alone, she recommends a quarter-sized blob (about one tablespoon). “I’ve seen some people suggesting lower quantities, like a nickel-sized dollop or one to two teaspoons, but that’s not quite enough because you want to make sure you’re also covering your ears, along your hairline, and the back and front of your neck,” she says.
Dr. Gohara notes that it can also be helpful to make a mental checklist of areas that are commonly forgotten, like the lips, ears, tip of the nose, and eyelids. This brings me to one of her golden application rules: Every part of your body that’s exposed to UV light “should be covered [with either sunscreen or sun-protective clothing], regardless of weather conditions and regardless of skin color.”
One application isn’t enough.
The amount of sunscreen you use in a single application isn’t the only factor that matters when it comes to UV protection. Reapplication is key too: You should aim to add another coat every two hours when you’re spending time outside, and even more frequently (typically every 40 to 80 minutes, depending on what the label says) if you’re swimming or sweating, according to Dr. Gohara. And always use sunscreen that has broad-spectrum coverage—which means it will protect your skin from both UVA and UVB rays—and an SPF rating of 30 or higher, per the AAD.
Use your senses (specifically vision and touch).
Another pointer from Dr. Gohara: Pay attention to the texture and color of your skin after you apply SPF. “With many sunscreens, there’s almost a white or translucent sheen to the skin and you’ll be able to see where you’ve applied it, and maybe where you’ve missed,” she says.
Mineral sunscreens (which create a physical barrier on the skin that reflects UV light) are more likely to have this effect than chemical formulas (which absorb UV rays, altering their structure to reduce sun damage)—though it may be subtle since many brands aim to eliminate an obvious white cast.
As you’re applying, you can also often physically feel where your skin seems fully coated—and where it’s a little drier and may need more sunscreen, both experts say.
Pay attention to how many bottles you’re going through.
“One additional tip is if you are using the same bottle from month to month, you’re not using enough,” Dr. Gohara says—and that’s especially true in the summer, when outdoor activities are the norm. “You should go through multiple a year.” And remember, if you have a larger than “normal” body, you likely need even more sunscreen than smaller folks.
Using an example from the chart above, someone who is five foot five and weighs 250 pounds needs just over two ounces of sunscreen per application, so a six-ounce bottle might not even be enough for a day at the beach if that person is regularly swimming and/or sweating. (Depending on your needs, it might be more convenient to buy your SPF in larger containers, like Supergoop’s PLAY Everyday Lotion SPF 50 18-ounce pump, $68, Supergoop.)
Remember that sunscreen isn’t your only defense against UV rays.
Sunscreen is an important tool when it comes to protecting your skin, but it’s not the only one: Donning a wide-brimmed hat, wearing UPF clothing, and reaching for bright or dark-colored fabrics are also smart ways to protect yourself from UV radiation, according to the Skin Cancer Foundation. Seeking shade—especially when the sun’s rays are at their strongest (typically between 10 a.m. and 4 p.m.)—can help keep your skin safer too.
The bottom line
People come in a lot of shapes and sizes, and it’s a disservice to the majority of adults that the sun protection guidelines we have don’t take that diversity into account. For people who are larger than the Reference Man, this could mean that even if they do follow the AAD’s guidelines, they could still be using an insufficient amount of sunscreen and could therefore be at a heightened risk for skin cancer.
Unfortunately, we have a long way to go when it comes to getting inclusive medical recommendations that consider people of all sizes. But in the meantime, I hope this article gives you a better idea of how much sunscreen your body might need, as well as some other tips to make sure you’re adequately covered. Just don’t forget to reapply.
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