How Important Is Sunscreen, Really?

A woman with brown hair sunbathes by sitting in a pool.  Her bathing suit is blue and she is wearing sunglasses.  Cultivated banana trees are in the background.

We’ve all seen the advice from dermatologists: wear sunscreen every time, all the time. But how important is it? And furthermore, what is this mass use of sunscreen’s effect on the environment? It turns out the answer is kinda complicated.

What does sunscreen do?

Sunscreen blocks the sun’s ultraviolet (UV) rays. Why is this important? Because UV light damages cell’s DNA. This causes sunburn, premature aging, and even cancer.
Within your cells, UV light initiates a reaction between two molecules of thymine, one of the four bases that make up DNA. The result, called a thymine dimer, is usually repaired by your body pretty quickly and efficiently. However, the more UV rays you get, the more thymine dimers you get, and the more you get, the likelier the body is to miss one or repair it incorrectly.
If the cell is disrupted because of an incorrect repair or remaining damage, it can’t carry out its normal functions. At this point, depending on the extent and location of the damage, there are two possibilities. If damage is widespread, the cell will die. If it is not too extensive, the cell becomes cancerous.
But UV rays are not all bad. Your body needs them to synthesize vitamin D (though Vitamin D can also be acquired through fatty fish and egg yolks) and studies have shown that people who lack access to the proper amount of sunlight can even get seasonal affective disorder (SAD).

So how to judge how much sunlight you can get, and how does sunscreen affect this? The answer depends on your skin.

As you can see, even if you are type VI, your skin can only stand up to the glare of the sun for one hour before being overwhelmed. People with type I skin should just become vampires, because honestly the sun hates you so much that you’re already half way there. But if you have to go outside, sunscreen can prevent you from a weekend of slathering on aloe and wincing every time you lay down.

How does sunscreen work?

A trucker with one side of his face exposed to the sun over the course of his career.  The sun exposed side is much more aged than the non exposed side.
The man in the picture had been a delivery truck driver for 28 years with the effects
of sun exposure being predominantly on one side of his face.

Sunscreen comes in two types, physical ingredients and chemical ingredients. Physical sunscreen ingredients (including the minerals titanium dioxide and zinc oxide) block and scatter the rays before they penetrate your skin. This is the type of sunscreen that you rub on and is usually a white color and thick texture. This sunscreen is safe for babies over six months (even babies need to wear sunscreen daily!), pregnant women, and people with sensitive skin. This sunscreen does come in spray on versions, but is often quite pricey when it does. When rubbing this on, make sure that you rub generous amounts on, as it only protects skin that it is completely covered.

Meanwhile, chemical sunscreen ingredients (like avobenzone and octisalate) absorb UV rays and dissipate them as heat before they can damage your skin. This usually comes in a spray on bottle, and is super convenient for every day use. But with all that convenience, comes the cost. Lots of ingredients are required to create both UVA and UVB protection and the higher SPFs, so you have a greater chance of having an allergy or sensitivity to a certain ingredient. Spray sunscreen with less ingredients tends to only protect against UVB rays. All these chemicals make this type of sunscreen more prone to clogging pores and causing break outs. These ingredients can also have some pretty weird side effects on the endocrine system. Plus, as of 2020, the FDA has announced that only zinc oxide and titanium dioxide are safe and effective for blocking the sun, so make sure your sunscreen contains these ingredients at a minimum.

So once you’ve chosen what type of sunscreen to use, you still have to chose which SPF. SPF is a measurement of how well that sunscreen will protect you. So a SPF of 15 provides about 15 times more protection than your skin without any sunscreen. Meanwhile, 50 SPF will provide 50 times more protection than just skin. Higher SPF numbers do mean more protection, but the higher you go, the smaller the difference becomes. SPF 15 sunscreens filter out about 93% of UVB rays, while SPF 30 sunscreens filter out about 97%, SPF 50 sunscreens about 98%, and SPF 100 about 99%. Unfortunately, even the most powerful of sunscreens only last about two hours before needing to be reapplied. Even worse, Consumer Reports found that when 82 brands were tested, 32 had less than half their labeled SPF.

But I don’t need sunscreen! and other lies you tell yourself.

Two pictures compare twins, the one on the got less sun exposure than the one on the right.  The twin on the right looks significantly older.
Twin B (right) had approximately 10 hours per week greater sun exposure than Twin A (left). The perceived age difference was more than eleven years (natural age 61) Study.

But it’s cloudy out/one day won’t hurt/I tan so beautifully and easily, I hear you cry. But by forgetting or ignoring your sunscreen, you’re writing checks that your skin has to cash.
“The purpose of using a sunscreen is to reduce the risk of sun damage, including pre-cancerous lesions and skin cancers, but to also reduce signs of aging caused by the sun, including wrinkles, fine lines, blotchy skin, thinning skin, loss of collagen, loss of elastin, sun spots, and redness,” says Kenneth Mark, M.D., board-certified cosmetic dermatologist and skin cancer expert in NYC.

So sunscreen every day, and don’t expect cloudy days or SPF make up to save you. Being water vapor, clouds don’t block UV rays very well and up to 80% of them can get through on a cloudy day.
“It’s best to think of the sunscreen in your moisturizer, BB or CC cream, foundation, or other cosmetics just a bonus, ” says Dr. Doppelt, a board certified dermatologist who is the head of Southeastern Dermatology. Not only is the sunscreen in most of these products not broad spectrum, but most people don’t apply their products in the necessary quantities to needed for meaningful protection anyway.

But what if you are absolutely, positively out of sunscreen and all the stores are all closed forever but you still have to venture outside to gather food and medical supplies while dodging mutants? Then you physically block out the sun. As long as you are not near the water (which will bounce the rays at you from a different angle than just from above), umbrellas block most UV rays. A standard rain umbrella blocks 77% of UV lights, 91% if it’s black. A travel sun umbrella works even better, blocking more than 99 percent of UV rays. UV rays are strongest between the hours of 10 a.m. and 4 p.m, so limit when you’re outside during these times. A good rule of thumb is that if your shadow is shorter than you, seek shade.
Other ways to protect yourself include wearing wide-brimmed hats and sun-protective clothing. Sun protective clothing makers will provide UPF labels, which indicate exactly how much of the sun’s rays the garment can shield. Look for The Skin Cancer Foundation’s Seal of Recommendation, which they only give to fabrics with a UPF of 30 or above.
If you don’t have sun protection clothing, regular clothes might or might not cut it. Clothing’s sun protection ability varies on several different conditions. Thin or light-weight fabrics can allow sunlight to filter through and reach your skin. If you can see light through it, then UV rays can get through. Color also affects how well you’ll be protected.  Dark colored fabrics absorb more of the sun’s rays than light colored fabrics. So goths unite! Your thick black clothing is protecting you way better than a yellow sun dress.

So how much should I use?

Picture of actress Jennifer Aniston
Jennifer Aniston is 51 years old and has the skin of a teenager because she
uses sunscreen like the sun is personally trying to assassinate her.

If you’re using sunscreen 100% correctly, for quick outings like walking the dog or driving to work in an office building, you’ll only need SPF of 15. For extended outdoor activities like distance running, hiking, swimming, sports, or working outdoors, SPF 30 is a must. But most likely, you’re not using it correctly. In order to correctly apply sunscreen, The American Academy of Dermatology Association recommends that you apply enough sunscreen to cover all skin that clothing will not cover. You’ll need about 1 ounce — or enough to fill an entire shot glass — to fully cover your body. Make sure to not forget your feet, your neck, your ears, and the top of your head. That’s right, you even sunscreen your part and your hair. Plus, you need to reapply every two hours, no exceptions.
The American Cancer Society notes that no sunscreens are waterproof or “sweatproof,” and manufacturers are not allowed to claim that they are. If a product’s front label makes claims of being water resistant, it must specify whether it lasts for 40 minutes or 80 minutes while swimming or sweating. Sunscreen usually rubs off when you towel yourself dry, so you’ll need to put more on.

But since you’re not using sunscreen correctly, you need to use a more powerful SPF than if you were. 30 is the minimum for quick forays into the outside world, but use nothing less than 50 if you’re going to be outside for more than fifteen minutes. And don’t forget your lips. To protect your lips from cancer, apply a lip balm or lipstick that contains sunscreen with an SPF of 30 or higher.

But isn’t sunscreen bad for the environment?

Sadly, yes. In a 2016 study, a team of international scientists found that Oxybenzone, or BP-3, is highly toxic to juvenile corals and other marine life. Oxybenzone is found in more than 3,500 skin care products. The compound enters the water through both wastewater effluent (like when you shower at home), and directly from swimmers wearing sunscreens.
Physical sunscreens can be dangerous too. Nano-size particles (which help physical UV-blockers absorb better on the skin) and clear zinc technologies are toxic to aquatic species.

Chart describing the effects of sunscreen on marine life

So what can you do? One, read the ingredients. “The active ingredients in chemical sunscreens tend to be the most problematic, though preservatives, such as parabens, can also pose an environmental threat”, recommends Craig Downs, Ph.D., a forensic ecotoxicologist in Virginia. Avoid oxybenzone (the most common compound found in sunscreens), octinoxate (which is even more toxic than oxybenzone, but also found in lower concentrations), and octocrylene.
Zinc oxide and titanium dioxide aren’t entirely worry-free options. When those ingredients are uncoated and nano-size (less than 35 nanometers in diameter), they can enter the cells of invertebrates and cause oxidative stress in sunlight. “This blows up the cells so they die,” says Downs. Your best bet is to go for coated, non-nano ingredients larger than 150 nanometers. At that point, “the toxicity drops off and there’s very little threat,” notes Downs. While the non-nano claim is not FDA regulated, look for brands that have data to back it up on their websites.
Better yet, look for the “Protect Land + Sea” Certification. The Protect Land + Sea Certification (PL+S) is different from other certification programs, such as Organic, Fairtrade, etc. These certifications ask the manufacturer to guarantee a product abides by its criteria, but Protect Land + Sea Certified Products, on the other hand, are independently tested by Haeretics Environmental Laboratory (HEL) to ensure they do not contain anything on the HEL list. The HEL list is a list of chemicals that are known pollutants in many different environments (freshwater streams, river, beaches, and ocean systems) or wildlife (e.g., corals, fish, birds, marine mammals, sea turtles).
And since science is ever changing and updating as new information becomes available, PL+S Product Certifications last for only two years. New chemicals are added to the HEL list at the beginning of every new Certification period. This means that companies have to re-certify their products to keep up with the science.

But be wary of ‘greenwashing‘. Companies will make claims, either by outright lying or by making the claim so vague as to be worthless, that they are environmentally friendly. “I searched for products that wouldn’t harm underwater ecosystems,” says Autumn Blum, a cosmetic chemist who launched Stream2Sea, a line of biodegradable sunscreens . “I was surprised to see sunscreens labeled ‘reef-safe’ containing ingredients I knew were not, in fact, safe.”
And just because something is natural, doesn’t mean it’s safe. Plant-based oils added to sunscreens, like eucalyptus and lavender, are dangerous to invertebrates. Beeswax can contain industrial insecticides that, when emulsified in beauty products, can unleash these chemicals on your skin and in the water. So when researching new products while wanting to do your part for the environment and your skin, the simpler the formula, the better.

Is sunscreen safe for you?

A woman covered by a blue hat lays on the beach in front of the ocean

Having done all this research and talked to all these oncologists and dermatologists and toxicologists, I can say with 100% certainly that you should use adequate amounts of sunscreen every day, and with proper reapplications every two hours. But you should keep in mind that when the FDA began to consider sunscreen safety, it grandfathered in active ingredients from the late 1970s without reviewing the evidence of their potential hazards. So in February 2019, when the agency released its final draft of sunscreens ingredient safety, 12 of the 16 sunscreen filters allowed for use in the U.S. were noted to have too little data to be recognized as safe and effective.
The most worrisome chemical without enough data was oxybenzone. In lab studies, it is a weak estrogen and has potent anti-androgenic effects. Animal studies report lower sperm counts and sperm abnormalities after oxybenzone and octinoxate exposure; delayed puberty after octinoxate exposure; and altered estrous cycling for female mice exposed to oxybenzone.

So, in conclusion, to be safe, only use physical sunscreens with titanium dioxide and zinc oxide from companies that allow their products to be tested by outside labs. I get no kickbacks from this, but in the interest of disseminating accurate information, companies that have passed include Olen Skin Care, Stream2Sea, and Badger Balm. If you have any questions, or want to submit another sunscreen as being safe for people and the environment, leave a comment.


A huge thanks to all of the government and university funded research that has been made available to the public for free.
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