For patients with rosacea or another skin condition that worsens with sun exposure, sunscreens are an important part of management. It's no wonder there are so many sunscreens out there. For consumers, it can be daunting staring down a drugstore aisle and picking the right sunscreen.
Sun Protection Factor (SPF) - What It Is and Why It Matters
SPF is the most recognizable number that is useful to understand. There's a common misconception that an SPF of 15 means you can stay in the sun 15 times longer without getting a sunburn. In reality, SPF is a ratio of how much more solar energy your skin can tolerate with a sunscreen compared with bare skin. As the SPF goes up, the more UVB your sunscreen blocks. Confused? Don’t worry, even dermatologists miss the nuances of what SPF means.1
Consumers should know that SPF is measured in the lab using a standardized UVB radiation source emitting energy at a set amount. Also, the sunscreen is applied at a set amount (2 mg per cm2) to the skin. In reality, the sun does not produce energy at a constant rate. As the sun gets stronger in midday, you skin will be subjected to more energy per unit of time. This is why the "15 times longer" doesn't really hold up for a sunscreen product with an SPF of 15.
Is a sunscreen with SPF 30 twice as strong as a sunscreen with SPF 15?
The answer is kind of. For a sunscreen with SPF 30, you get 1/30th of the UVB rays. With a SPF 15, you get 1/15th of the UVB rays. When looking at it this way, the SPF 30 sunscreen is "twice" as strong as the SPF 15 sunscreen. In reality, what this fraction means is that for an SPF 30 sunscreen you're protected from 97% of UVB rays. For an SPF 15 sunscreen, you're already protected from 93% of UVB rays. By doubling the SPF, you block an additional 4% of UVB rays.
I still tell my patients that by getting a sunscreen with a higher SPF, they are taking out an "extra insurance policy" that their sunscreen is going to keep them protected. In the real world, it's hard to remember to apply enough and reapply frequently enough for every person in the family. A higher SPF sunscreen gives you a buffer. There are some studies that show an SPF of 50 in a split-face study in preventing sunburn.2 Also, a higher SPF doesn’t mean the price is higher for popular sunscreens.3
With that being said, I warn patients that buying an SPF 100 sunscreen doesn't mean they can reapply less frequently or stay out longer in the sun than they would ordinarily. Some scientists have demonstrated this misguided behavior with higher SPF products.4 This would defeat the purpose.
Bottom line on SPF:
- A higher SPF does mean more protection but only from UVB rays. Natural sun has both UVB and UVA rays - but more about that later.
- As the SPF goes up, you get a diminishing amount of benefit. In other words, a product with SPF 100 only provides a small benefit, from a lab testing perspective, over a product with SPF 30 with regard to blocking UVB rays. But in the real world, a higher SPF is likely to provide more protection to regard the risk of sunburn.
- SPF is a lab-generated value that does not always apply to the real world.
Why Broad Spectrum Matters - Blocking Harmful UVB and UVA Rays
Sunlight is composed of both UVB and UVA rays. UVB rays are the type that cause sunburns and drive skin cancers. UVA rays penetrate deeper, drive skin photoaging, and likely contribute to skin cancers as well. SPF does not tell you anything about whether a sunscreen blocks UVA. The FDA allows sunscreen manufacturers to label their products "broad spectrum" only if they demonstrate in bench testing that their products also block the longer UVA rays. This is an important feature to look for in any sunscreen product. If I had a choice between a sunscreen with an SPF of 100 but no broad-spectrum protection and a sunscreen with an SPF 30 but with broad-spectrum protection, I would buy the SPF 30 broad-spectrum sunscreen for me and my family.
Using Enough, Applying Frequently, and Watching Out for Water
In the real world, the effectiveness of sunscreens in preventing sunburns, decreasing the risk of skin cancer, and reducing photo-damage means much more than SPF and broad-spectrum.
One simple rule is to use enough. In lab testing of sunscreens, the FDA ensures that every test subject gets a standard amount of sunscreen. In the real world, many parents can only throw sunscreen at their kids minutes before they jump into the pool. Studies have shown that in the real world, consumers use about ½ or less of the recommended amount of sunscreen.5 The average adult in swim trunks needs a shot glass full of sunscreen to cover exposed skin for one application.
If it's hot out or there is a pool involved, consumers have to make sure the sunscreen they pick is water-resistant. Water and sweat dilute or wash away sunscreens, decreasing their effectiveness. Consumers should pay attention to how long the sunscreen is rated for water resistance. Once the 40 or 80 minutes are up, it's time to apply another shot glass. If water isn't involved, consumers still often don't reapply frequently enough. Remember, it isn't about time but energy delivered to the skin. When the sun is the highest, reapplying sunscreens frequently is even more important.
Give time for sunscreens to work into the skin - a sunburn can happen in minutes in areas with a high UV index. Dermatologists recommend waiting at least 15 minutes (30 minutes is ideal) before going out after putting on sunscreen.
Finally, pick a product you and your family actually like. It's important that a product smells nice, feels good on your skin, does not cause irritation, and rubs in well. Researchers have shown that these factors are critical in determining the popularity of sunscreen products.
Picking the Right Sunscreen - What I Do:
- SPF is very important, but it's not the only thing you should think about. Pick an SPF 30 or higher. A higher SPF buys you a little more protection.
- Pick a product with "broad spectrum" on the label.
- Use enough. Reapply frequently enough.
- If there is going to be water or sweating, pay attention to the water resistance rating.
- Select a product you can afford that smells nice, doesn't cause skin irritation, and feels good on your skin.
Here are the 3 of the most affordable sunscreens that are popular with consumers and provide the right amount of protection.3 They are all lotions of SPF 45 or above, with broad-spectrum protection and a water resistance rating of 80 minutes. Average cost is $0.74 per ounce.
They all meet AAD sunscreen criteria.6
- NO-AD Sunscreen Lotion, SPF 45
- NO-AD Sport Sunscreen Lotion, SPF 50
- Banana Boat Sunscreen Sport Family Size Broad Spectrum Sun Care Sunscreen Lotion, SPF 50
- Herzog SM, Lim HW, Williams MS, de Maddalena ID, Osterwalder U, Surber C. Sun protection factor communication of sunscreen effectiveness: A web-based study of perception of effectiveness by dermatologists. JAMA Dermatol. 2017 Feb 1. doi: 10.1001/jamadermatol.2016.4924. [PubMed]
- Russak JE, Chen T, Appa Y, Rigel DS. A comparison of sunburn protection of high-sun protection factor (SPF) sunscreens: SPF 85 sunscreen is significantly more protective than SPF 50. J Am Acad Dermatol. 2010;62(2):348-349. doi: 10.1016/j.jaad.2009.05.025. [PubMed]
- Xu S, Kwa M, Agarwal A, Rademaker A, Kundu RV. Sunscreen product performance and other determinants of consumer preferences. JAMA Dermatol. 2016;152(8):920-927. doi: 10.1001/jamadermatol.2016.2344. [PubMed]
- Autier P, Doré JF, Négrier S, et al. Sunscreen use and duration of sun exposure: a double-blind, randomized trial. J Natl Cancer Inst. 1999;91(15):1304-1309. [PubMed]
- Autier P, Boniol M, Severi G, Doré JF; European Organization for Research and Treatment of Cancer Melanoma Co-operative Group. Quantity of sunscreen used by European students. Br J Dermatol. 2001;144(2):288-291. [PubMed]
- How to select a sunscreen. American Academy of Dermatology website. https://www.aad.org/public/spot-skin-cancer/learn-about-skin-cancer/prevent/how-to-select-a-sunscreen Accessed February 10, 2017.