Everyday Sun Protection: A Guide to Choosing Sunscreen

Everyday Sun Protection: A Guide to Choosing Sunscreen

Sunscreen is an essential component of any skincare routine, providing protection against the sun's damaging rays and serving as the foundation of an anti-aging regimen. But simply applying a layer in the morning isn't enough - there are many factors to consider when it comes to properly using sunscreen. In this article, we'll delve into the specifics of reading labels, determining proper usage, and applying sunscreen correctly, ensuring that you're able to fully benefit from this key product.

Types of sunscreen

As we detail in our article on sunscreen, these protective products work by preventing the sun's harmful UV rays from reaching and damaging the DNA within your skin cells. Sunscreens utilize chemicals such as oxybenzone, avobenzone, octisalate, and octinoxate to absorb UV rays that reach the skin's surface, while sunblocks contain tiny particles of minerals such as zinc and titanium that sit on top of the skin and reflect the sun's rays. However, these reflective ingredients can also lead to a heavy or white cast on the skin, though there are now many products that aim to minimize these effects.

Some people prefer chemical-based sunscreens, which tend to have a lighter, more elegant feel. There is some debate over whether chemical sunscreen ingredients pose potential health risks due to their absorption into the body with regular use, but it is also true that some chemical sunscreens may offer broader UV protection than pure mineral sunblocks. Ultimately, the choice between mineral and chemical sunscreens comes down to personal preference. Many products formulated for sensitive skin, including those for babies or children, are mineral-based.

Reading sunscreen labels 

In the United States, sunscreens are considered an over-the-counter drug, regulated by the Food and Drug Administration (FDA), so unlike cosmetic products, the labels are strictly regulated. Let’s look at the important terms to look for when selecting a product: SPF (sun protection factor), broad spectrum, and water-resistant and sweat-resistant. 

Understanding and choosing an SPF

In the US, the SPF (Sun Protection Factor) of a sunscreen refers to its ability to block UVB rays, which can cause sunburn and DNA damage that increases the risk of skin cancer. Generally, the higher the SPF, the greater the protection. SPF is intended to extend the length of time you can stay in the sun without getting burned. For example, if your skin would normally burn after 15 minutes in the sun, applying an SPF 30 sunscreen would extend that period by 30 times. However, it's important to remember that no sunscreen is perfect - even an SPF 100 still allows some UV rays to pass through.

While you might assume that using a product with the highest possible SPF is the best option, it's worth noting that SPF protection levels off after a certain point. For example, SPF 30 blocks about 97% of UVB rays, SPF 50 blocks about 98%, and SPF 100 blocks about 99%. As a result, for most people, a product labeled SPF 30-50 is sufficient. Another factor to consider is that many products rated above SPF 50 contain chemical filters, so if you're concerned about the absorption of chemical sunscreen ingredients, it's worth considering the amount you'll be using if you plan on reapplying regularly.

Why is it important to choose “broad-spectrum”? 

SPF is not the only factor to consider when selecting a sunscreen - for optimal skin protection, you need protection from both UVB and UVA rays. While UVB rays cause sunburn and DNA damage, UVA rays penetrate deeper into the skin and can lead to skin pigmentation and the formation of deeper wrinkles. Sunscreens labeled "broad-spectrum" offer some level of UVA protection, but unfortunately in the US, there is no label or scale to inform consumers about a product's level of UVA coverage (unlike the SPF labeling system for UVB coverage). In contrast, other countries have rating scales that indicate UVA protection, such as the "PA" system in Asia (with "PA++++" being the maximum level of UVA protection).

The US Food and Drug Administration (FDA) states that it is currently studying the safety of newer sunscreen filters, including the UVA blockers used abroad, but many experts believe that US sunscreens are currently behind the times in this regard. Therefore, for now, it's always a good idea to choose a product labeled "broad-spectrum" to ensure you're getting some level of UVA protection in addition to UVB protection.

How often should sunscreen be reapplied? 

In the US, sunscreen products are tested in a laboratory setting where SPF is determined. This SPF value is calculated based on a standardized process that involves applying the product at a thickness of 2 milligrams per square centimeter of skin. This thickness is sufficient to provide protection for about two hours. Practically speaking, this might mean that if you apply a layer in the morning under makeup, you should strongly consider reapplying sunscreen to exposed areas to maintain your protection by noon at the latest—and especially if you go out for lunch or an afternoon run. It's important to remember that real-world conditions can affect the effectiveness of sunscreen. For example, if you're sweating heavily, wiping with a towel, or go swimming, your sunscreen will need to be applied more frequently. If you’re at the beach all day, you’ll definitely want to reapply every few hours for maximum coverage.

It's a good idea to reapply sunscreen to ensure that you're fully protected. Additionally, if you're spending a full day at the beach, it's a good idea to reapply every few hours to maintain maximum coverage. So the next time you head out into the sun, don't forget to slather on some sunscreen and keep yourself safe!

Do "water-resistant" and "sweat-resistant" mean anything?

The terms “water-resistant” and “sweat-resistant” are allowed on labels if the product is formulated to stay on wet skin and provide protection for either 40 or 80 minutes – the label will state which applies. (In 2011 the FDA disallowed the use of the terms “waterproof” and “sweatproof”, as really no sunscreens are completely waterproof). Practically, what does this mean? It means that if you’re going for a run or swim, slather on a sunscreen that is rated for 80 minutes, and then reapply every 90 minutes to 2 hours that you are in the water or anytime after sweating heavily.   

How much sunscreen is necessary? 

Remember how SPF is determined by applying sunscreen at 2 milligrams per square centimeter of skin? That may not sound like a lot, but it translates into more than most people use regularly - about ½ to ¾ a teaspoon for your face and neck alone, and 1 ounce for a full adult body. For daily use, you’ll probably use about 1-1.5 teaspoons for your face, neck, ears, hands, and chest (exposed areas). If covering larger body areas,  you’ll need more than you might think - up to 1 teaspoon per arm, and 1-2 teaspoons for each leg, the back, and the chest and abdomen (up to a shot glass for the whole body). On your face, remember that sunscreen goes on after treatment serums, but before makeup. When it’s time to reapply your sunscreen, you should be using these same amounts 

We hope this deep dive into sunscreen helps you understand the important factors when choosing a product to protect your skin. Choose a broad-spectrum, SPF 30 sunscreen that you like the feel and look of, that fits into your daily routine, and that fits your budget. Apply your sunscreen evenly and generously to exposed skin, and remember to reapply every 2 hours and sooner if swimming or sweating heavily, and consider using sun protective clothing to cover exposed areas as well (hats, sun jackets.) The bottom line is, the best sunscreen is one that you will use regularly. Your favorite celebrity’s recommended sunscreen may seem nice, but if you don’t like the way it feels on your skin or if it’s too expensive, you might not use it regularly or liberally enough. If you still have questions, make sure to bring them up with your dermatologist.


Disclaimer: As with all the information on this site, this article 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.