Dermatologist's Guide To Choosing and Using Sunscreen

Dermatologist's Guide To Choosing and Using Sunscreen

Sunscreen is one of the most important parts of your skincare routine. One could argue it’s the foundation of anti-aging and wearing it daily - 365 days a year, rain or shine - is probably the single best thing you can do for the health of your skin. Super simple! Yet, like many other things in skincare, sunscreen can be super confusing - mineral or chemical? What SPF should you look for? How much do I use? Don’t worry! We’ve got you covered. We’ll go over the difference between sunblocks and sunscreens, common ingredients in sunscreen, how these protect your skin, and considerations when choosing one for daily use. 

Sunblock vs. Sunscreen 

Most people use these terms interchangeably, but in reality there is a difference between sunscreen and sunblock, and the names hint at that difference: they have different mechanisms. Two types of ingredients are used to prevent the sun’s UV rays from reaching, and damaging, the skin. Physical blockers use tiny mineral particles (for this reason they’re also called mineral sunblocks) like zinc oxide and titanium dioxide that sit on top of the skin and reflect UV rays. Unfortunately these opaque ingredients are also the reason sunscreens often cause  a whitening effect, or a white cast. Luckily, there are now many products available that are specially formulated to minimize this. However, most mineral or physical sunblocks still feel heavier and thicker than most chemical sunscreens. Cosmetic factors aside, many with sensitive skin find that physical sunblocks are more suitable for their skin. This is why most sun products formulated for babies and children use zinc and titanium as the active ingredients!

Chemical sunscreens use ingredients like oxybenzone, avobenzone, octisalate, octocrylene, octinoxate, and homosalate that work by absorbing UV rays as they hit the skin. These chemicals break the rings of the UV rays, dissipating the UV energy and releasing that energy as heat. Chemical sunscreens are great at protecting the skin and in some cases have slightly broader ultraviolet coverage than physical sunblocks. They tend to be thinner and lighter, offering a more elegant feel, and are used widely in cosmetic formulations. The downsides to chemical sunscreens? There is some evidence these chemicals can be absorbed into the body with regular, repeated use, especially over large body areas. And sometimes, that chemical reaction and heat release can lead to irritation, especially for sensitive skin types. In rare cases one can also be sensitive or allergic to certain chemical sunscreens (most commonly oxybenzone but also sometimes octocrylene, avobenzone, and of course certain fragrances or preservatives. Finally, there are chemical sunscreen ingredients are banned in some places due to environmental concerns. If a label refers to “reef safe” ingredients, it means that those banned chemicals are excluded. 

Why is ultraviolet radiation dangerous to the skin anyway? And what does broad spectrum mean? 

The reason dermatologists are so insistent about sunscreen is because they reduce exposure to ultraviolet (UV) rays from the sun. These rays are part of the electromagnetic radiation spectrum emitted from the sun, and the relevant portions are UVC (200-290 nanometers, or nm), UVB (290-310 nm), and UVA (320-400 nm). Visible light, which the naked eye can see, is 400-800 nm. Fortunately, the earth’s atmosphere blocks all UVC, most UVB, but none of the UVA rays. UV rays affect our skin in various ways: UVB rays cause sunburn and DNA damage, and increase risk of developing skin cancers. UVA causes skin pigmentation and formation of deeper wrinkles as it penetrates deeper into the skin, damages cell DNA by causing radical oxygen species formation, increases inflammation, and affects the immune system’s ability to respond to these damaged cells. 

Sunscreens block UV rays and their harmful effects on the skin. In the US, sunscreens are required to be labeled with SPF, or sun protection factor, which only refers to the product’s UVB coverage. Sunscreen with SPF 15 blocks 93% of UVB rays and SPF 30 blocks 97%. This protection levels off - SPF 50 blocks 98% and SPF 100 blocks 99% of UV rays, and most  sunscreens rated above SPF 50 are chemical based, so consider the amount you’ll be using if you reapply at the recommended intervals (roughly every 2 hours). Most folks do fine with a product that is labeled SPF 30-50.  For maximum skin protection, you need protection from UVB and UVA rays. Unfortunately in the US, there is no label or scale to inform you about a product’s level of UVA coverage other than the term broad-spectrum, which indicates that the product blocks at least some UVA. This is decidedly not the case abroad, where Asian sunscreens have a PA+++ rating scale. The FDA states it is still studying multiple sunscreen ingredients used abroad for safety, but most experts agree that US sunscreens are years behind the times when it comes to new sunscreen ingredients. So for now, unless you have a trip abroad planned where you can stock up on sunscreens from overseas, make sure you see “broad spectrum” on any sunscreen product you purchase in the United States.

For physical sunblocks, zinc oxide offers broad-spectrum coverage of both UVA and UVB, while titanium dioxide is better at UVB coverage, so often you’ll find products mixing the two, or using zinc alone. Chemical sunscreen ingredients mostly “specialize” in one part of the UVA/UVB spectrum, and so most products will contain several in order to offer the best combined UVA and UVB coverage. 

Are chemical sunscreens risky? 

While chemical sunscreens provide great UVR protection, there is some  mild controversy over whether they can affect human health in other ways. It’s been shown that the body does absorb some chemical sunscreen ingredients with regular use over large body areas, and with reapplication. That doesn’t necessarily mean these chemicals are harmful, and it’s reassuring that recent large-scale reviews in the United States as well as Europe show no conclusive evidence linking chemicals such as oxybenzone or octinoxate to health problems. In both analyses, the experts note that studies showing potential changes in thyroid or kidney function with exposure to oxybenzone come from the lab, and the same effects have not been seen in human studies. That being said, there is ongoing research in this area. We will point out here that the sun is a proven carcinogen - as vital as it is to human life - so sunscreen used properly does reduce your risk of skin cancer. If you are worried about the unknown effects of chemical sunscreens, we recommend you stick to mineral sunscreens for daily use, use sun protective clothing as much as possible, and reserve the chemical sunscreens for occasions where you need the lighter, sheerer formulations. 

What about absorption of nano metals in physical sunscreens? 

Many people prefer to use physical sunscreens to lower exposure to chemicals, but dislike the white cast these products may produce. To minimize the whitening effect, some manufacturers use nanonized, or micronized particles of zinc and titanium in the sunblocks. These smaller particles help mitigate the whitening but there has been some controversy over whether these tiny metal particles pose health risks. The concern is that these much smaller particles may penetrate the skin and be absorbed into the body. Fortunately, the body of current evidence shows that when sunblocks are applied to intact skin, these tiny metal pieces just can’t make it past the skin barrier and remain in the stratum corneum, or top layer of skin. The only time micronized metals may pose a higher risk is when used in spray products that are accidentally inhaled, thus posing a risk to the lungs. This is reflected in the European Union’s classification of titanium dioxide as a safe ingredient. If in doubt, don’t apply sunblock to areas of broken skin - cover that area with sun protective clothing instead.

If you’re struggling with sensitive skin, look for a physical or mineral sunblock to add to your routine. Remember that sunscreen should typically be used as the last step of your skincare routine, after any treatment serums or moisturizers, but under makeup. These come in a wide variety of price points and formulations, but if you have very dry skin, you can often find moisturizing products with SPF built in, and those seeking a light, sheer foundation look may find tinted sunblocks helpful as the last morning skincare step. 

For those with darker skin tones, there are many sunscreen products formulated with different tints to suit all skin tones. Tinted sunscreens may also offer additional protection because in addition to the included sun protective factor, they usually contain iron oxide, which is used to color foundations and makeup but also happens to reflect visible light and may help reduce flaring of pigmentary disorders such as melasma or other conditions that worsen with exposure to visible light. It’s a win-win!

For those with acne-prone skin, mineral sunblocks may be less likely to induce a  breakout as chemical sunscreens sometimes cause sensitivity directions. Also, you may want to look for oil-free on the label of the product to reduce risk of having a reaction. 

A final word on choosing sunscreen: the above factors are important when considering which product to incorporate into your daily routine, but in the end, the best product is the one you’ll actually use consistently and correctly! Your friend may rave about a $70 product but if you find yourself using 3 drops of it because you want the bottle to last, you aren’t getting anywhere near the SPF factor on the label, which makes it less effective at protecting your skin. Or, you may choose a mineral sunblock for its environmental profile, but because it leaves a white cast, you hesitate to use it daily or don’t apply nearly enough to protect your skin. We recommend that you focus on finding a broad-spectrum, SPF 30-50 sunblock that fits your budget and texture preferences. Choose one that you will like using daily over treatment serums and under makeup (if you wear it). If you really dislike mineral products, choose a chemical sunscreen for the face and then consider a physical sunblock for use on larger body areas or when spending extended time outdoors. Better yet, cover up exposed skin with sun protective clothing like a rashguard or leggings

Ok, I’ve picked a sunscreen. How do I use it properly?

When using sunscreen, apply liberally, and evenly, to all exposed skin - and you’ll need more than you might think! For the average adult, you need ½-1 teaspoon for the face and neck, 1 teaspoon for an arm, 1-2 teaspoons for a leg, or the back, or chest and abdomen - this adds up to nearly a shot glass for your entire body.  Now you see why finding a product you like and will use correctly is important! Don’t forget to reapply sunscreen after 2 hours or after swimming or sweating. And of course, if you have specific health concerns, ask your dermatologist - we’re always happy to point you in the right direction. 


Disclaimer: As with all of the information on this site, this post is meant to be for informational and educational purposes only, and is not medical advice. When in doubt, please ask your physician.

Teresa Fu, M.D.

Dr. Teresa Fu is a board certified dermatologist and mother of two. She graduated from Stanford Medical School and practices in the San Francisco Bay Area.