Following a survey, a study published in 2015 in JAMA Dermatology reveals that less than half of the participants know how to correctly read a sunscreen label, and only 43% understand what the SPF index means. This finding highlights a lack of information that can confuse consumers when faced with the variety of sun protection products available. Many end up making their choice randomly, without paying attention to the essential indications. So, what exactly does the SPF correspond to? In this article, we will together decode what this key term means.

Sun Protection: What is SPF and what does it mean?
Sunscreen labeling: What is the purpose of the SPF symbol and the following number?
Primary sunscreens are products primarily used to protect against UV rays (e.g., beach sun care products), whereas for secondary sunscreens this is not the case (e.g., tinted skin care products, lipsticks, etc.).
Introduced in 1934, the SPF index, an abbreviation for "Sun Protection Factor," is a indicator numeric measure of a sunscreen's effectiveness in blocking erythemal UV rays that cause sunburn. It is typically expressed on a scale ranging from 2 to 50+, the latter representing the highest level of protection. However, labeling rules can vary by country. Due to frequent consumer confusion about the actual effectiveness and duration of sunscreen protection, several countries have implemented labeling rules.
Is there a difference between the acronyms IP, SPF, and FPS? In reality, these three terms refer to the same concept: the level of protection provided by a sunscreen against UV rays responsible for actinic erythema. The acronym FPS stands for "Facteur de Protection Solaire" in French, while SPF is its English equivalent (Sunburn Protection Factor). The abbreviation IP, for "Protection Index", is also used, especially in some French-speaking countries. Regardless of the brand or the country where you purchase your sunscreen, it is a universal value.
Country | Permitted SPF Value |
---|---|
European Union (in accordance with the Cosmetics Regulation (EC) No. 1223/2009) | Minimum SPF of 6; SPFs > 50 should be indicated as SPF 50+ |
United States (in accordance with the FDA's final rule, 2011) | Minimum SPF of 2; broad-spectrum sun products with SPF values from 2 to 14 must be labeled with a "Skin Cancer/Aging Alert" warning; SPF 60+ is the maximum SPF indicated on the label |
Australia / New Zealand (in accordance with the AS/NZS 2604:2021 standard) | Minimum SPF of 4; maximum allowed value indicated on the SPF label is 50+ for products with SPF ≥ 60 only; can display prevention claims (cancers, keratoses, sun spots) if broad-spectrum sunscreen with an SPF ≥ 30; minimum SPF of 15 for secondary sunscreens |
Canada (according to Health Canada, Sunscreen Monograph Reference Document, 2012) | Minimum SPF of 2; SPFs > 50 should be indicated as SPF 50+; sunscreens without broad-spectrum protection or sunscreens with an SPF < 15 must carry a warning label "Skin Cancer/Aging Alert" |
Japan (as per the JCIA) | Minimum SPF of 2; SPFs > 50 should be indicated as SPF 50+; claims such as "prevents wrinkles" are prohibited |
China (according to the CFDA) | Minimum SPF of 2; SPFs > 50 should be indicated as SPF 50+ |
Although useful, this measure remains "imperfect". This globally accepted standard primarily reflects the ability of a sunscreen to prevent certain UV rays from "burning" the skin. More specifically, it refers to the amount of solar energy required to produce a slight redness on protected skin, in accordance with the ideal conditions for sunscreen use, compared to that required on skin completely devoid of sun protection. However, it does not take into account the effects of the remaining UV rays, which can also contribute to the premature aging of the skin (photoaging) and the formation of skin cancers (photocarcinogenesis).
It is often read that UVB rays are the cause of sunburns. However, erythemal UV rays are composed of 85% UVB (between 290 and 320 nm) and 15% UVA-II (between 315 and 340 nm).
Contrary to popular belief, the SPF does not represent the duration one can stay in the sun without risk. Indeed, many consumers think that if a person starts to slightly redden after 10 minutes spent outside without sun protection, applying an SPF 50 sunscreen would theoretically allow them to stay in the sun 50 times longer before getting a sunburn. This means they could stay in the sun for 8 hours without getting sunburned (10 minutes * 50 = 500 minutes) and about twice as long as with an SPF 30.
However, this is a misconception. The SPF is related to a received and filtered solar energy dose, not a fixed duration. Several factors can affect the degree of sunscreen protection: the intensity of UV radiation at a given time and place, the phototype, the amount of sunscreen applied, the activities carried out (swimming, etc.), the intake of certain medications, or even the frequency of reapplication. That's why even a product displaying a high SPF must be applied generously and regularly to maintain optimal protection.
In addition to clearly labeling the SPF, sunscreens must also provide a description of the level of protection they offer (low, medium, high, or very high) on the same label.
Level of Protection | Measured SPF | SPF claimed on the label |
---|---|---|
Minimal protection | 4 - 14.9 | Four, Six, Ten |
Moderate protection | 15 - 29.9 | 15, 20, 25 |
High Protection | 30 - 59.9 | 30, 50 |
Very high protection | Greater than or equal to 60 | 50+ |
But then, what does the number visible after the SPF correspond to?
The number following the SPF label indicates the percentage of erythemal UV rays blocked. The higher it is, the greater the percentage of UV light it blocks. Indeed, an SPF 50 means that 1/50 of the erythemal UV rays will reach the skin, assuming that the sunscreen has been correctly applied, or that the user is protected 50 times better than without sunscreen. However, many believe that a high SPF offers twice, or even three times the protection of an SPF 30, thus giving a false sense of security.
In reality, the increase in protection is not linear. An SPF 30 already provides nearly optimal protection when applied correctly, blocking about 97% of erythemal UV rays. An SPF 50, on the other hand, blocks about 98%, and an SPF 100 about 99%. Thus, the difference in protection between an SPF 30 and an SPF 50 is minimal (about 1%) and does not provide substantial protection. However, although the gains in protection are marginal, they can become significant for sensitive skin, light phototypes, or in contexts of frequent or prolonged exposure.
Therefore, it is crucial not to rely solely on the SPF, but also on the product's formulation, particularly the "broad spectrum" label that includes long UVA rays, as well as proper application and regular reapplication to maintain effective sun protection.
Sun Protection Factor Value | Percentage of UV rays blocked by the sunscreen | Quantity of UV rays not blocked by the sunscreen |
---|---|---|
SPF 2 | 50% | 50% |
SPF 15 | 93.3% | 6.7% |
SPF 20 | 95% | 5% |
SPF 30 | 96.7% | 3.3% |
SPF 50 | 98% | 2% |
SPF 80 | 98.75% | 1.25% |
SPF 100 | 99% | 1% |
It's important to remember that no sunscreen can block 100% of erythemal UV rays, thus providing complete protection from sunburn and the resulting skin damage.
How is the SPF value of a sunscreen determined?
To determine the SPF of a sunscreen, rigorous tests in vivo in the laboratory (ISO 24444) are conducted on a non-tanned skin area of volunteers (e.g., inner part of the arm). The sunscreen is then generously applied (2 mg/cm2 of skin), and then exposed to an artificial source of UV rays (solar simulator) for approximately 20 minutes.
In Europe, the Sun Protection Factor (SPF) is accepted if it is determined based on at least 10 subjects.
After 24 to 48 hours, the exposed areas of the skin are examined, and the fraction of UV radiation that will produce a slight redness with and without sun protection is measured. The SPF value is determined by dividing the amount of UV rays needed to cause a slight sunburn on protected and unprotected skin.
Although it is the current SPF test, several test methods in vitro will soon be implemented: the in vitro "double plate" method (ISO 23675) and the hybrid diffuse reflectance spectroscopy method (HDRS - ISO 23698) are in the final phase of international standardization. They are expected to become the first ISO standards published for SPF tests in vitro.
While laboratory testing is fairly effective in determining the SPF of a sunscreen, it only provides an indication of its effectiveness against erythemal rays and not against UVA rays, which penetrate deeper.
The essential takeaway on SPF.
The Sun Protection Factor (SPF) can be regarded as the "protection factor against sunburn".
The number following the FPS notation indicates the amount of erythemal UV rays filtered by a sunscreen.
The higher the FPS, the more the additional benefits decrease.
It is recommended to use a sunscreen with an SPF of at least 30 on all exposed skin areas daily.
No sunscreen can filter out 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).
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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