Based on a survey, a 2015 study published in JAMA Dermatology found that fewer than half of participants could interpret a sunscreen label and only 43% understood the meaning of the SPF rating. This reveals an information gap that can confuse users faced with the variety of sun care products. Many choose at random and overlook essential details. What does SPF indicate? In this article, we explain this key term.
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Sunscreen protection: what is SPF and what does it mean?
Summary
Published June 23, 2021,
updated on June 23, 2025,
by
Stéphanie, PhD, Doctorate in Life and Health Sciences
—
11 min read
Sunscreen labeling: what do SPF and the following number indicate?
The primary sunscreens are products used to protect against UV rays (e.g., beach sunscreens), whereas for the secondary sunscreens this is not the case (e.g., tinted skin care, lipsticks, etc.).
Introduced in the 1960s by Franz Greiter, the SPF value—short for Sun Protection Factor—is a indicator numeric measure of a sunscreen’s effectiveness at blocking erythemal UV rays that cause sunburns. It is expressed on a scale ranging from 2 to 50+, the latter representing the highest level of protection. However, labeling regulations can vary by country. Because consumer confusion about actual effectiveness and duration of protection is common, several countries have implemented labeling standards.
Is there a difference between the acronyms IP, SPF, and FPS? These three terms refer to the same concept: the level of protection a sunscreen offers against UV rays that cause actinic erythema. The acronym FPS corresponds to "Sun Protection Factor" in French, while SPF is its English equivalent (Sunburn Protection Factor). The abbreviation IP, for "Protection Index", is also used in some French-speaking countries. Regardless of the brand or country where you buy your sunscreen, it is a universal value.
| Country | Authorized SPF value |
|---|---|
| European Union (in accordance with Cosmetics Regulation (EC) No. 1223/2009) | Minimum SPF 6; SPF values above 50 should be indicated as SPF 50+ |
| United States (per the FDA final rule, 2011) | Minimum SPF of 2. Broad-spectrum sunscreens with SPF values from 2 to 14 must carry a “Skin cancer/skin aging alert” warning. SPF 60+ is the maximum SPF displayed on the label. |
| Australia / New Zealand (in accordance with AS/NZS 2604:2021 standard) | Minimum SPF of four; maximum label value of SPF 50+ applies only to products with SPF ≥ 60; may display prevention claims (cancer, keratoses, sun spots) if broad-spectrum sunscreen with SPF ≥ 30; minimum SPF of 15 for secondary sunscreens |
| Canada (according to Health Canada, Reference Monograph on Sunscreens, 2012) | Minimum SPF 2; SPFs > 50 must be listed as SPF 50+; sunscreens without broad-spectrum protection or with SPF < 15 must carry the warning "Skin cancer/skin aging alert" |
| Japan (according to the JCIA) | Minimum SPF of 2; SPF values above 50 must be labeled SPF 50+; claims such as “prevents wrinkles” are prohibited. |
| China (according to the CFDA) | Minimum SPF of 2; SPF values greater than 50 must be indicated as SPF 50+. |
Sunscreen labeling guidelines by country.
Source: Pirotta G. Sunscreen Regulation in the World. The Handbook of Environmental Chemistry. Springer International Publishing (2020)
Although useful, this measure remains "imperfect". This global standard reflects a sunscreen’s ability to prevent certain UV rays from "burning" the skin. More precisely, it refers to the amount of solar energy needed to cause a slight reddening on protected skin, in line with ideal sunscreen application conditions, compared with that required on unprotected skin. However, it does not account for the effects of residual UV rays, which can also contribute to premature skin aging (photoaging) and skin cancer formation (photocarcinogenesis).
Sunburn is often attributed to UVB rays. However, erythemal UV radiation consists of 85% UVB (between 290 and 320 nm) and 15% UVA-II (between 315 and 340 nm).
Contrary to a common belief, SPF does not indicate the safe duration of sun exposure. Indeed, many consumers think that if someone begins to redden after 10 minutes outdoors without sunscreen, applying SPF 50 would allow 50 times longer exposure before a sunburn. That means about eight hours in the sun without burning (10 minutes * 50 = 500 minutes), roughly twice as long as with SPF 30.
However, this is a misconception. SPF is linked to a dose of solar energy received and filtered, not to a fixed duration. Multiple factors can affect sunscreen protection: the intensity of UV radiation at a given time and place, phototype, the amount of sunscreen applied, activities such as swimming, certain medications, and reapplication frequency. This is why a product with a high SPF must be applied in sufficient amount and at regular intervals to maintain consistent protection.
In addition to clear SPF labeling, sunscreens must also include a description of the protection level they provide (low, medium, high, or very high) on the same label.
| Protection level | Measured SPF | SPF value stated on the label |
|---|---|---|
| Low protection | 4 – 14.9 | |
| Moderate protection | 15 - 29,9 | 15, 20, 25 |
| High protection | ||
| Very high protection | ⩾ 60 |
Categories of sunscreens based on SPF.
Source: Australian Government – Department of Health and Aged Care. Australian regulatory guidelines for sunscreens (2023).
So what does the number displayed after SPF represent?
The number after SPF indicates the percentage of erythemal UV rays blocked. The higher the number, the more UV light it blocks. SPF 50 means 1/50 of erythemal UV reaches the skin, assuming correct sunscreen application, or that the skin is 50 times more protected than without sunscreen. Many believe high SPF offers two or three times the protection of SPF 30, creating a false sense of security.
In reality, The increase in protection is not linearSPF 30 offers near-optimal protection when applied correctly, blocking about 97% of erythema-causing UV rays. SPF 50 blocks about 98% and SPF 100 about 99%. Thus the difference in protection between SPF 30 and SPF 50 is minimal (about 1%) and does not provide substantial additional coverage. However, marginal gains can become significant for sensitive skin, lighter phototypes, or during frequent or prolonged exposure.
Effective sun protection requires more than SPF. It relies on product formulation, including the term “broad spectrum,” which covers long UVA—proper application, and regular reapplication.
| SPF value | Percentage of UV radiation blocked by sunscreen | Amount of UV rays not blocked by sunscreen |
|---|---|---|
| SPF 2 | ||
| SPF 15 | … 93,3% | 6,7% |
| SPF 20 | 95% | tags, including 5% |
| SPF 30 | tags and values such as 96,7% | … 3,3% |
| SPF 50 | ` tags) so I can translate it while preserving the tags and the `98% | … 2% |
| SPF 80 | 98.75% | |
| SPF 100 | 99% | 1% |
Amount of erythemal UV blocked or transmitted by sunscreen at different SPFs.
Source: Silva dos Reis V. M. et al. Sun protection factor: meaning and controversies. Anais Brasileiros de Dermatologia (2011)
No sunscreen can block 100% of erythemogenic UV rays or prevent sunburn and resulting skin damage.
How is the SPF value of a sunscreen determined?
To determine a sunscreen’s SPF, rigorous tests in vivo in a laboratory (ISO 24444) are performed on an unexposed skin area of volunteers (e.g., inner arm). The sunscreen is applied at 2 mg/cm2 of skin, then exposed to an artificial UV source (solar simulator) for 20 minutes.
In Europe, SPF is accepted if determined on at least ten subjects.
After 24 to 48 hours, the exposed skin areas are examined and the UV dose that causes slight redness with and without sunscreen is measured. The SPF value is calculated by dividing the UV dose required to cause a mild sunburn on protected skin by the dose required on unprotected skin.
Although this is the current SPF test, several test methods in vitro will soon be applied: the in vitro "double plate" (ISO 23675) and the hybrid diffuse reflectance spectroscopy (HDRS – ISO 23698) method are in the final stage of international standardization. They are expected to become the first ISO standards published for in vitro SPF testing in vitro.
Although laboratory testing determines a sunscreen’s SPF, it only indicates efficacy against erythemal rays and not against the UVA, which penetrate deeper skin layers.
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Essential information on SPF.
Sun protection factor (SPF) can be considered the "protection factor against sunburn".
The number after SPF indicates the amount of erythema-inducing UV rays filtered by a sunscreen.
The higher the SPF, the fewer additional benefits.
We recommend daily use of a sunscreen with an SPF of at least 30 on all exposed skin areas.
No sunscreen filters 100% of the UV rays that cause sunburn.
Sources
DOWDY J. C. & al. Simplified method to substantiate SPF labeling for sunscreen products. Photodermatology, Photoimmunology and Photomedecine (2003).
SILVA DOS REIS V M. & al. Sun protection factor: meaning and controversies. Anais Brasileiros de Dermatologia (2011).
BILODEAU D. & al. Beyond UV radiation: A skin under challenge. International Journal of Cosmetic Science (2013).
OSLIN D. W. & al. Minimal erythema dose (MED) testing. Journal of Visualized Experiments (2013).
KUNDU R. V. & al. Assessment of consumer knowledge of new sunscreen labels. JAMA Dermatology (2015).
LIM H. W. & al. Sunscreens: An update. American Journal of Clinical Dermatology (2017).
RIGEL D. S. & al. 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 American Academy of Dermatology (2018).
PIROTTA G. Sunscreen regulation in the world. The Handbook of Environmental Chemistry. Springer International Publishing (2020).
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