In this article:
What is the “two finger” rule for sunscreen?
Can I get a higher SPF by combining two SPF products?
Do I need to wear sunscreen when on the computer or in front of screens?
Is waterproof or sweatproof sunscreen better than water-resistant sunscreen?
Can supplements help boost a suncare routine?
Do I need to be more cognizant of wearing SPF when I’m on a plane or visiting the mountains?
Do you need to wear sunscreen under clothing?
So, you’ve mastered the suncare basics. You know the difference between mineral and synthetic sunscreens and even have a SPF reapplication reminder set on your phone. You might even be the go-to source for skin care and sunscreen tips in your friend group.
Congrats! It looks like you’re ready to level-up your sunscreen knowledge. Can you achieve a higher SPF through combining sunscreens? And can all those “SPF supplements” out there really shield our skin from damage?
To answer those questions and help you wade through all the advanced-suncare facts (and myths) out there, we tapped board-certified dermatologists Dr. Corey L. Hartman and Dr. Beth McLellan to guide us through what to know about sunscreen.
Time to dive head-first into our dermatologist-led intermediate guide to sunscreen!
What is the “two finger” rule for sunscreen?
The “two finger” rule for sunscreen is exactly what it sounds like: a guide to help you apply an adequate amount of SPF to your face that requires applying sunscreen to the entire length of two of your fingers (usually your pointer and middle).
So, is this an okay method for application? Yes, it is, if you “apply from the crease where your finger meets your hand to the fingertip,” says Dr. McLellan. Be generous with your coating! “Add a third finger to include the neck,” adds Dr. Hartman.
This method isn’t just a popular TikTok hack–it has roots in research. “A study from 2016 established the recommendation that the entire body requires about an ounce of sunscreen, or about a shot glass amount, for adequate protection. If you consider that the face is about 4-5% of the body's surface area then the face should receive about 0.05 ounces of product to provide enough protection,” explains Dr. Hartman (1). “Since it isn’t feasible to measure that amount each day, it’s been suggested that about two finger lengths of sunscreen is about the amount (0.05 ounces) necessary to protect the face.”
Ultimately, no application guideline is perfect, so the key point to keep in mind is to apply an even layer of sunscreen to all exposed areas. And if in doubt, it’s never a bad idea to apply more!
Can I get a higher SPF by combining two SPF products?
Yes and no! Did we confuse you there? Let’s clear it up...
“Unfortunately, getting a higher SPF is not that simple. Merely adding the different SPF numbers for different products won’t give the total sum of the numbers in sun protection,” says Dr. Hartman. “The good news is that although the math may not add up exactly right, there is always a benefit to adding extra layers of protection."
Dr. McLellan points out “combining sunscreens can sometimes make re-application easier. For example, people may start the day with a lotion but find it easier to re-apply using a powder.”
However, there is a caveat: You should be cognizant of what types of sunscreens you’re layering. Research has suggested that combining synthetic sunscreens with mineral sunscreens can prompt instability in synthetic filters, leading to a decrease in the ingredient’s SPF abilities (2). So, when layering sunscreens combine similar ingredients with one another for ultimate protection.
Do I need to wear sunscreen when on the computer or in front of screens?
“Blue and green light can play an important role in causing unwanted pigmentation so protection from these light sources is especially important in people trying to lessen hyperpigmentation,” explains Dr. McLellan (3). Unfortunately, it doesn’t end there. Research also suggests that blue light can cause skin barrier disruption and trans epidermal water (moisture) loss (4).
What can you do? “Current recommendations suggest that even in front of screens sunscreen should be applied, particularly one with iron oxides (tinted sunscreens) which may protect against HEV more effectively than other filters,” adds Dr. Hartman.
Is waterproof or sweatproof sunscreen better than water-resistant sunscreen?
Let’s cut right to the chase: There’s no such thing as waterproof sunscreen (5).
“The best that we can achieve in formulation of sunscreen products is water-resistant, at least so far,” says Dr. Hartman. Water-resistant sunscreens can tolerate wet or sweaty skin for anywhere from 40-80 minutes and must undergo testing, outlined by the US Food and Drug Administration, to be able to label themselves as such (6).
Although these sunscreens hold up better when put up against sweat and water Dr. McLellan reminds us that “reapplication of sunscreen after swimming or other water activities is crucial to maintain effective sun protection.”
Can supplements help boost a suncare routine?
Supplements can’t replace a broad-spectrum SPF, however, supplements rich in antioxidants can help boost skin’s defences against environmental aggressors- like UV rays. “Research shows that certain vitamins can act as antioxidants which can be helpful in protecting the skin from the breakdown of collagen that leads to photoageing,” explains Dr. Hartman.
So, which antioxidant-rich supplements are best for fortifying skin against pro-ageing external players? “A board-certified dermatologist can help advise on the best supplements to maintain healthy skin,” says Dr. McLellan.
Dr. Hartman suggests exploring Polypodium leucotomas. He elaborates, “Polypodium leucotomos is a tropical fern from Central and South America. Its leaves contain antioxidants and other compounds that may protect against skin damage caused by inflammation and unstable molecules called free radicals” (7). Consult your health care provider before starting any new supplements.
Do I need to be more cognizant of wearing SPF when I’m on a plane or visiting the mountains?
“UV exposure increases at high altitudes so you may find your skin is more sensitive to the effects of the sun when in the mountains,” says Dr. McLellan. The board-certified dermatologist adds, “Similarly, UV exposure through airplane windows can be significant. Some studies have even shown elevated risks of skin cancers in pilots and flight crew members” (8). However, it’s worth noting data supporting this goes back several decades, before the mid-1990s availability of sunscreens with broad spectrum sun protection.
To protect yourself from stronger UV rays Dr. McLellan suggests application (and reapplication) of a broad-spectrum sunscreen SPF and when on a plane, “consider closing the window shade to protect your skin.”
Don’t forget that mountains and air travel aren’t the only instances that require more diligent suncare. Dr. Hartman reminds us, “Any situation that places one closer to either the equator or the sun makes UV rays more potent.”
Do you need to wear sunscreen under clothing?
Yes! “Regular clothing provides very minimal sun protection,” explains Dr. McLellan. “Wearing SPF underneath with significant sun exposure is a good idea.”
If slathering on sunscreen underneath your clothing doesn’t sound appealing, worry not! You have another option: UV protective clothing (9). Sun-protective fabric doesn't use SPF as a measurement, but instead uses Ultraviolet Protection Factor (UPF), which takes into account the amount of both UVA and UVB rays that can penetrate a fabric and reach your skin. A solid UPF to shoot for is 30, with 50 being the gold standard.
But UPF clothing can’t cover everything! McLellan reminds us, “It is also important to apply SPF to all areas not covered by the clothing – often the face and hands.”
Learn more about sunscreen.
References for this information:
- American Journal of Epidemiology, May 2016, pages 824-833
- Photochemical & Photobiological Sciences, October 2021, pages 1,273-1,285
- Photodermatology, Photoimmunology and Photomedicine, May 2018, pages 184-193
- Journal of Cosmetic Dermatology, March 2021, pages 714-717
- American Academy of Dermatology, Accessed July 2023, Webpage
- U.S. Food and Drug Administration, Accessed July 2023, Webpage
- The Journal of Clinical and Aesthetic Dermatology, February 2021, pages 50-60
- British Journal of Dermatology, July 2019, pages 55-64
- Skin Cancer Foundation, Accessed July 2023, Webpage
