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Signification du sigle SPF.

SPF 20, 30, 50: What Does It Mean?

It is common to see the indications SPF 20, 30 or 50 on the packaging of sun creams. It is also not uncommon to find them on the bottles or tubes of certain skincare products and makeup. Cosmetologists advise to pay attention to these numbers which accompany the mention "SPF". But what do they correspond to? And why are they important?

IP, SPF, FPS: What Are These Acronyms For?

The IP, SPF or FPS indications are often confusing. Some users are bewildered by the multitude of sun protection products available on the market and often end up choosing one at random without really caring about the indications displayed. In reality, there is no difference between IP, SPF or FPS. These terms mean exactly the same thing: SPF stands for "Sun Protection Factor", FPS stands for "Facteur de Protection Solaire" and IP stands for "Protection Index". Thus, the number written on your tube of sunscreen has the same value, regardless of the brand or the country where you bought it: it is therefore a universal value.

Each of these indications represents the level of protection/efficiency of a sunscreen product against UVB-induced sunburn. What is interesting, therefore, is not the letters but rather the numbers that precede them. There are four levels of SPF:

  • From 6 to 15 for a weak protection;

  • From 15 to 25 for a medium protection;

  • From 30 to 50 for a high protection;

  • From 50+ for a very high protection.

These protection indexes are the ratio between the time of exposure necessary to induce a sunburn with and without cream. If, for example, a person develops redness after 5 minutes of exposure without sun protection, the application of an SPF 50 sun cream multiplied by 50 the time of exposure before getting a sunburn (5 minutes * 50 = 250 minutes). This means that it will then, in theory, take 250 minutes, or 4 hours and 10 minutes, to get a sunburn with the sunscreen. However, these estimates have some drawbacks. Indeed, certain factors can weaken or even eliminate the action of the cream, such as poor application, insufficient quantity of sun cream, perspiration, swimming, rubbing with the towel or clothing, etc... They are only effective under ideal conditions. This is why it is important to apply them regularly to protect your skin.

It is important to remember that no protection can completely stop the sun's rays. These sun protection indices can also tell us how much UVB is blocked by your sun protection product. That's why, even when we're wearing sunscreen, we still get a tan.

For example, an SPF 15 product blocks about 95% of UV rays, an SPF 30 protects you against 96.7% of UVB, while an SPF 50 stops about 98.3% of UVB.

For example, this means that a sunscreen product with SPF 30 absorbs about 97% of UVB, while the remaining 3% penetrates the skin.

In other words, the higher the SPF, the more UV will be blocked by the product, the less it will penetrate your skin so the more protected you are.

How To Choose Your SPF?

The choice of sun protection to be applied depends on various criteria: 

  • The phototype: The lighter the skin, the higher the level of protection should be. Darker skin tones, which are less vulnerable to UV rays, can do without maximum protection when they are not subjected to prolonged and repeated exposure to the sun.

  • The season: Even in winter, the application of a sunscreen is necessary because UV rays pass through clouds: a cloudy veil lets 90% or more of UV rays through. On the other hand, it is possible to afford to use a medium protection.

  • Time of day: Since the sun's power varies according to the time of day, it is possible to alternate SPF levels throughout the day. In the morning and late evening, it is possible to use medium protection if you are outdoors. On the other hand, between 11am and about 3pm, you should use screens with a higher SPF, especially in summer: this is when UVB rays are strongest.

  • Geographical area: People living in tropical areas, where the sun is bright all year round and most of the day, need to protect themselves from the sun properly. In addition to an SPF 50 cream, it is best to reduce sun exposure.

Sources

  • DOWDY J. C. & al. Simplified method to substantiate SPF labeling for sunscreen products. Photodermatology, Photoimmunology and Photomedecine (2003).

  • LIM H. W. & al. Sunscreens: An update. American Journal of Clinical Dermatology (2017).

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