Is SPF 100 a Scam? The Truth Behind High SPF Sunscreens
If you’ve ever shopped for sunscreen, you’ve probably seen bottles labeled SPF 30, SPF 50, at most SPF 50++. But in some countries, you’ll find sunscreens boasting SPF 100, 110, or even 130 - numbers that seem to promise unbeatable protection from the sun.
It sounds great, right? After all, SPF 100 must be twice as protective as SPF 50, right?
Not exactly.
What Does SPF Actually Measure?
SPF, or Sun Protection Factor, is one of the most misunderstood numbers in skincare. Many people assume that higher SPF means dramatically better protection, but that’s not how it works.
SPF is a multiplier of UVB exposure, not a time extension (1). I wrongly assumed that if your skin could tolerate sun for 5 minutes before starting to burn, then with SPF 15 it could withstand 5x15=75 minutes, and with SPF 30 it could withstand 5x30=150 minutes. Well, that's not exactly right.
The SPF number tells you how much more UVB exposure your skin can tolerate before burning, compared to bare skin. It does not mean you can stay in the sun 100 times longer with SPF 100. Here is how SPF is measured (2):
(Minimal Erythemal Dose (MED) on protected skin)
SPF = -------------------------------------------------------------------------
(Minimal Erythemal Dose (MED) on unprotected skin)
- Minimal Erythemal Dose (MED) = The amount of UV radiation needed to cause visible redness.
- SPF 100 means it takes 100 times more UVB radiation to cause a burn compared to bare skin.
- SPF 50 means it takes 50 times more UVB radiation to cause a burn.
At first glance, SPF 100 seems like a big improvement over SPF 50—but in reality, it only blocks about 1% more UVB rays. UVB protection does not increase linearly—it follows a diminishing returns curve.
| SPF Level | UVB Radiation Blocked | UVB That Still Reaches Skin |
|---|---|---|
| SPF 15 | 93% | 7% |
| SPF 30 | 96.7% | 3.3% |
| SPF 50 | 98% | 2% |
| SPF 100 | 99% | 1% |
This happens because SPF measures how much UV radiation reaches the skin, not how much is blocked. Here’s the key difference:
- SPF 50 allows 1/50th (2%) of UVB radiation to reach the skin.
- SPF 100 allows 1/100th (1%) of UVB radiation to reach the skin.
While SPF 100 reduces UVB exposure by half compared to SPF 50, the difference in absolute UVB blocking is only 1% more protection—because SPF 50 already blocks 98% of UVB rays, leaving very little left to block.
This is why dermatologists and regulatory agencies often say that SPF 50 is already sufficient—because the increase in protection is minimal, but the risk of misuse (thinking you don’t need to reapply if you have a higher SPF) increases.
Why Some Countries Allow SPF 100 (and Others Don’t)
SPF 100 sunscreens are available in some countries but banned in others. This isn’t because they don’t work, but because different health agencies have different approaches to sunscreen regulation and consumer protection.
The European Union and Australia cap SPF labeling at 50+ to prevent misleading claims (3,4), since SPF 50 already blocks 98% of UVB rays, while SPF 100 blocks 99%—a negligible difference in real-world protection. Studies show that people using high-SPF sunscreens tend to stay in the sun longer (5), leading to greater UV exposure despite the higher SPF. To counteract this, some countries limit SPF claims to 50+ to encourage correct usage rather than relying on high numbers for a false sense of security.
In contrast, countries like the US, China, and some parts of Latin America allow SPF 100+ on labels as long as the sunscreen meets testing standards. The reasoning is that most people don’t apply enough sunscreen, so a higher SPF may help compensate for under-application - and there are studies that support this (6,7).
Even in regions where SPF 100 is "banned," the formulas themselves are not. In the EU and Australia, an SPF 100 sunscreen can still be sold, but it must be labeled SPF 50+ to comply with regulations. This means that if a brand sells SPF 100 in the US and SPF 50+ in Europe, the product may be exactly the same—the only difference is the label. The goal of these regulations isn’t to stop consumers from using high-SPF products but to prevent misleading marketing and ensure people focus on proper application and reapplication, which matter far more than chasing higher SPF numbers.
What about UVA (the silent killer)?
SPF (Sun Protection Factor) measures protection against UVB rays, the type of ultraviolet radiation responsible for sunburn and direct DNA damage leading to non-melanoma skin cancers.
UVB rays primarily affect the outer layers of the skin, causing visible sunburn. SPF testing is based on erythema (redness), which is triggered by UVB exposure, making it a straightforward way to measure how much UVB protection a sunscreen provides. It does not account for UVA protection. UVA rays, on the other hand, penetrate deeper into the skin, damaging collagen and elastin, leading to wrinkles, sagging, hyperpigmentation, and an increased risk of melanoma (8,9) (the deadliest type of skin cancer). Unlike UVB, UVA is present all day, year-round, and penetrates through clouds and glass.
Why Isn’t There a Universal UVA Protection Rating?
Unlike UVB protection, which is easy to measure using erythema response, UVA exposure does not cause an immediate, visible reaction like sunburn. This makes it harder to quantify its protection factor in a simple, standardized way. However, several methods exist:
- In the EU, Australia, and Japan, broad-spectrum sunscreens must provide UVA protection equal to at least one-third of their SPF rating, determined through in vitro tests like critical wavelength assessment (a measure of how much of the UVA spectrum a sunscreen absorbs) (10,11).
- Persistent Pigment Darkening (PPD), used in the PA+ system (common in Japan and South Korea), evaluates how long it takes for UVA exposure to cause lasting pigmentation. PA+ to PA++++ rankings indicate increasing levels of UVA protection (12).
- In the US, the FDA only requires a pass/fail “broad-spectrum” designation, with no clear UVA protection scale (13).
The lack of a globally standardized UVA rating makes it difficult for consumers to assess how much protection a sunscreen provides beyond its SPF value. While SPF 100 may prevent sunburn better than SPF 50, it does not necessarily mean superior UVA protection, which is why dermatologists recommend choosing broad-spectrum sunscreens with proven UVA filters instead of focusing solely on SPF numbers.
So, what's the veredict? Is SPF 100 worth it?
The difference in UVB blocking between SPF 50 and SPF 100 is just 1%, and the added protection is often outweighed by the risk of misuse. SPF 100 might be useful for high risk individuals, or in prolonged outdoor activities, mainly because higher SPF may help offset the fact that most people don't apply enough sunscreen, as indicated by so many studies to even be worth referencing (but I'll reference some anyway: (14,15)).
But even in those situations, you shouldn't forget that UVA exposure remains a concern: SPF only measures UVB protection. A broad-spectrum sunscreen with strong UVA filters is more important than just a high SPF number. SPF 100 isn’t a scam, but correct application and reapplication matter far more than the SPF number.
References
1.U.S. Food and Drug Administration. Sun Protection Factor (SPF). FDA. Sun Protection Factor (SPF) | FDA
2.Latha, M. S., Martis, J., Shobha, V., Sham Shinde, R., Bangera, S., Krishnankutty, B., Bellary, S., Varughese, S., Rao, P., & Kumar, B. R. (2013). Sunscreening agents: a review. Journal of Clinical and Aesthetic Dermatology, 6(1), 16–26. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3543289/
3.European Commission. Questions and Answers on the Commission Recommendation on the efficacy of sunscreen products and the claims made relating thereto. Press Release MEMO/07/282. Press corner | European Commission
4,11.Therapeutic Goods Administration. Australian regulatory guidelines for sunscreens. Australian Government Department of Health. https://www.tga.gov.au/publication/australian-regulatory-guidelines-sunscreens-args
5.Autier, P., Dore, J. F., Schifflers, E., Cesarini, J. P., Lejeune, F., Koelmel, K. F., ... & Lienard, D. (1999). Sunscreen use and duration of sun exposure: a double-blind, randomized trial. Journal of the National Cancer Institute, 91(15), 1304–1309. https://doi.org/10.1093/jnci/91.15.1304
6.Ou-Yang, H., Stanfield, J., Cole, C., Appa, Y., & Rigel, D. (2012). High-SPF sunscreens (SPF ≥ 70) may provide ultraviolet protection above minimal recommended levels by adequately compensating for lower sunscreen user application amounts. Journal of the American Academy of Dermatology, 67(6), 1220–1227. https://www.jaad.org/article/S0190-9622(12)00260-5/abstract
7.Williams, J. D., Maitra, P., Atillasoy, E., Wu, M. M., Farberg, A. S., & Rigel, D. S. (2018). SPF 100+ sunscreen is more protective against sunburn than SPF 50+ in actual use: Results of a randomized, double-blind, split-face, natural sunlight exposure clinical trial. Journal of the American Academy of Dermatology, 78(5), 902–910.e2. https://www.jaad.org/article/S0190-9622(17)32908-0/abstract
8.Qin, J., Holman, D. M., Jones, S. E., Berkowitz, Z., & Guy, G. P. (2023). Ambient ultraviolet A, ultraviolet B, and risk of melanoma in a nationwide United States cohort, 1984–2014. Journal of the National Cancer Institute, 116(12), 1928–1936. https://academic.oup.com/jnci/article-abstract/116/12/1928/7730113
9.Jin, S. G., Padron, F., & Pfeifer, G. P. (2022). UVA radiation, DNA damage, and melanoma. ACS Omega, 7(37), 32936–32948. https://pmc.ncbi.nlm.nih.gov/articles/PMC9494637/
10.European Commission. Commission Recommendation of 22 September 2006 on the efficacy of sunscreen products and the claims made relating thereto (2006/647/EC). Official Journal of the European Union. EUR-Lex - 32006H0647 - EN - EUR-Lex
12.Japan Cosmetic Industry Association. UV Protection Grade (PA) System. JCIA. https://www.jcia.org/en/common/download/top/jcia-notifications-spf-pa.pdf
13.U.S. Food and Drug Administration. Labeling and effectiveness testing: sunscreen drug products for over-the-counter human use. Federal Register, 76(117), 35620–35665. https://www.federalregister.gov/documents/2011/06/17/2011-14766/labeling-and-effectiveness-testing-sunscreen-drug-products-for-over-the-counter-human-use
14.Petersen, B., & Wulf, H. C. (2014). Application of sunscreen—Theory and reality. Photodermatology, Photoimmunology & Photomedicine, 30(2–3), 96–101. https://doi.org/10.1111/phpp.12099
15.Kim, S. M., Oh, B. H., Lee, Y. W., Choe, Y. B., & Ahn, K. J. (2010). The relation between the amount of sunscreen applied and the sun protection factor in Asian skin. Journal of the American Academy of Dermatology, 62(2), 218–222. https://doi.org/10.1016/j.jaad.2009.06.047