How do sunscreen labels work?
Are you clueless on how to read a sunscreen label? Do you want to be informed and confident when choosing the best sunscreen? This page will answer all of the questions you may have on how to read a sunscreen label and how to pick the best sunscreen. Undoubtedly, many people pick out a sunscreen based on the big number SPF number we see on the bottle. The SPF, or sun protection factor, of a product, is important. However, there are other important things to keep in mind. The main things to consider are:
Sun Protection Factor
Water Resistance and the amount of time covered
Broad Spectrum Coverage
How to Read A Sunscreen Label
Sun Protection Factor (SPF)
SPF is a measure of the minimal erythemal dose. On a related note, erythema is a medical term for redness. The minimal erythemal dose is the amount of ultraviolet radiation needed to cause visible redness on the skin. SPF is calculated by dividing the minimal erythemal dose with sunscreen by the minimal erythemal dose without sunscreen. (1)
However, this SPF number is based on a minimum concentration of sunscreen of 2mg per centimeter2 of skin. In reality, most people are applying between 0.5 and 1mg/cm2. There are 2 different theories on how SPF changes based on concentration. The exponential decrease model (1) and the linear relationship model. (2)
Let’s say you buy SPF 50 and only apply enough to get a concentration of 1mg/cm2, are you getting SPF 25 in that case? The answer is no; now you’ve applied SPF √50=7.07. What if you applied 0.5mg/cm2? You’re getting SPF ∜50=2.66.
You once again buy SPF 50, and yet again you only applied to a concentration of 1mg/cm2. In this model, the SPF is now 25 based on the assumption that concentration and SPF are linearly related.
If you’re going with the full shot glass amount for your body, this should be irrelevant because you’re applying the full 2mg/cm2. At least, I hope so.
Is a higher SPF better?
Yes, but it depends on what we’re talking about. I’ve heard and always read that there is not a linear relationship between increasing amounts of sun protection and increasing the SPF. For example, some people say SPF 60 isn’t twice as good as SPF 30.
This is actually a very common misconception among both patients and the medical community. A sunscreen with SPF 60 is twice as good as SPF30 when you think about it in a different way. SPF 30 filters out 96.7% of the UV radiation. Then, SPF 60 filters out 98.3% of that radiation. Therefore, SPF 60 is only able to filter 1.6% more UV radiation than SPF 30.
However, when we think about how much UV radiation is transmitted to the skin, SPF 30 allows 3.3% of UV rays to hit the skin. Meanwhile, SPF 60 will only allow 1.65% of the UV radiation to reach the skin. Therefore, SPF 60 cuts the amount of UV rays that hit the skin in half. That’s where you get HALF the dose of UV radiation.
Can you add SPF by layering on sunscreen?
For example, what happens when I add SPF 15 sunscreen to SPF 4 sunscreen?
You do not have SPF 19 from layering sunscreen that way. There is no cumulative addition of the SPF from different products.
What level of SPF should I look for in a sunscreen?
Consumers don’t use nearly as much sunscreen as recommended or necessary to achieve the sun protection factor labeled on the bottle. Countless studies have proven this. Just because you squirted a handful of sunscreen onto your hand, and used it to cover your entire trunk and arms doesn’t mean you’re protected to SPF 70. There is a minimum concentration that must be achieved on your skin for sunscreen’s protective powers to work as discussed above.
For this reason, I recommend that you splurge on the higher SPF sunscreens (70+). This is better than the SPF 30 that won’t be covering you to SPF 30 in reality. The higher SPF can compensate for the fact that most people don’t apply nearly enough sunscreen. Also, the application of sunscreen in the real world is not nearly as perfect as the way it is applied in most laboratory testing. (3) Sunscreen is like birth control. Theoretically, it should prevent 99% of pregnancies. But, people don’t use it the correct and perfect way every time.
The FDA is currently investigating whether they will ban sunscreen producers from labeling their products with anything greater than SPF 50. The final ruling should be out in the coming years.
Broad-spectrum sunscreen is able to block both UVA and UVB rays. UVB rays are the higher energy, more damaging ones. However, UVA is also implicated in skin cancer and aging. SPF only measures UVB blocking ability. There is no SPF rating scale for UVA rays. A star rating system for UVA has been proposed where 1 star is low protection, 2 stars for medium protection, 3 stars for high protection, and 4 stars for the maximum protection you can get in an over the counter product. (4) The FDA still hasn’t made any hard and fast rules regarding UVA labeling. We will see how this changes in the future. If you want to make sure there’s UVA protection in your sunscreen product, look for ingredients like ecamsule, avobenzone, and zinc oxide.
Due to new FDA regulations, waterproof sunscreens don’t exist anymore. (5) Sunscreens can now claim water resistance for either 40 or 80 minutes. This means you can expect the SPF claimed on the bottle for that amount of time while you are swimming or sweating.
Other Parts of the Sunscreen Label to Keep in Mind
Similarly, sunscreen can no longer be called sunblock.(5) Hence, you will no longer find waterproof sunscreens or sunblock. This is because sunscreen can never block out 100% of the UV rays.
Broad Spectrum and SPF 15+
Sunscreens that are both broad spectrum and SPF 15 or greater help to prevent sunburn. Furthermore, these sunscreens can claim that they prevent early aging and skin cancer on the label.
What about my SPF 4 Australian Gold with built in Bronzer?
Finally, there is no reason to wear tanning oil. If you have that stuff in your house please get rid of it. You’re lulling yourself into a false sense of security where you think that applying something has to be better than applying nothing at all. SPF 4 doesn’t protect against the sun in any significant way. This low level of protection can’t claim to prevent aging or skin cancer under the new FDA regulations. If you can’t go without the glisten your tanning oil provides, try putting your normal SPF 15+ sunscreen on first, and then adding a layer of tanning oil. Tanning oil is for tanning leather. You’re not trying to become leather, are you?
Don’t buy anything Australian Gold sells unless it has SPF 15 or more. On a side note, I do love their Soothing Aloe After Sun Gel. It feels amazing after you’ve been outside. It’s the only thing that won’t give my face a horrible burning sensation after a sunburn.
Did you learn how to read a sunscreen label? Do you have any other questions? Leave your comments below.
- Petersen B, Wulf HC. Application of sunscreen–theory and reality. Photodermatol Photoimmunol Photomed. 2014;30(2-3):96-101.
- Osterwalder U, Sohn M, Herzog B. Global state of sunscreens. Photodermatol Photoimmunol Photomed. 2014;30(2-3):62-80.
- Ou-yang H, Stanfield J, Cole C, Appa Y, Rigel D. High-SPF sunscreens (SPF ≥ 70) may provide ultraviolet protection above minimal recommended levels by adequately compensating for lower sunscreen user application amounts. J Am Acad Dermatol. 2012;67(6):1220-7.
- Osterwalder U, Herzog B. Sun protection factors: world wide confusion. Br J Dermatol. 2009;161 Suppl 3:13-24.