Contents / Sommaire
- 🇬🇧 SPF, PA+, PPD,… How UVA and UVB protections are measured and labeled in the world
- 🇫🇷 SPF, PA+, PPD… comment les protections contre les UVA et les UVB fonctionnent-elles ?
- 1. Protection UVB
- 2. La protection UVA
- F.A.Q. / Démystification de mythes
- 3. References
When choosing a sunscreen, we have to pay attention to the numbers and information on the packaging.
UVA or UVB protection, SPF, PPD, PA+,… what are the meaning of all of these? This article will tell you everything you need to know!
At the end, I have also added an in-process F.A.Q. which aim is to debunk myhts about sunscreens.
This article is the third part of the Sunscreens and Your Skin series which deals with everything related to sunscreens (how they work, how to use them, how to choose them…).
In the previous articles from the series, I have discussed:
- in Part 1, about what broadspectrum sunscreens are and what kinds of filters are included in them,
- in Part 2, about the differences between organic (or chemical) and inorganic (or physical) sunscreens as well as about micronisation (reduction of inorganic filters into nanoparticles), especially to avoid white cast.
- in Part 4, about some organic filters showing health risks.
If you are interested to know what sunscreens protect from, namely UV rays and their effects on the skin (skin aging, skin cancer…) you can access the thematic Ultraviolets and the Skin series.
🇬🇧 SPF, PA+, PPD,… How UVA and UVB protections are measured and labeled in the world
1. UVB protection
UVB rays are part of the ultraviolet radiation that a human eye can’t see. They are medium-wavelength, between 320 nm – 290 nm (nanometer) and are partially filtered by the Earth’s atmosphere. The part that reaches the Earth’s surface can have positive as well as deleterious effects on our skin like vitamin D synthesis, essential to our health, or skin burns.
a. UVB protection label
When sun protection was first developed, it was especially against UVB radiation as it causes sunburns, a quick and visible reaction, unlike UVA radiation (see more in the 2. UVA protection section).
Internationally, the UVB protection of a sunscreen is indicated by its Sun Protection Factor (SPF), a number. It’s usually the information that is the most eye-catching on the packaging. The higher the number is, the more protection against UVB rays the product gives.
What does it mean?
b. UVB protection (SPF) meaning
The SPF is measured as the ratio of the amount of UVB radiation required to cause an erythema (a slight burning) on a protected skin after application of 2mg/cm2 of product to that required to the same result on the same unprotected skin.
The SPF formula:
SPF = MED of protected skin / MED of unprotected skin
with MED = minimal erythemal dose (1).
Theoretically, when used in the correct amount, a product with SPF 30 will protect the skin until it is exposed to 30 times more UVB rays than that is required to burn the unprotected skin (2). In real-life, that is not always the case as the amount of product applied is usually less than the one the SPF measure is done with.
As seen in the image below, a product with:
- SPF 15 absorbs 93.3 % of UVB radiation
- SPF 30 absorbs 96.7 %,
- SPF 50 absorbs 98 %.
The formula to calculate sunscreen percentage absorption is (3):
- Absorption = 100 – (100/SPF).
As the SPF is only used to indicate a UVB protection, it’s not an indicator of the UVA protection. Thus, other techniques must be used to assess the UVA protection.
2. UVA protection
UVA rays are also part of the ultraviolet radiation. They are long-wavelength, between 320 nm – 400 nm (nanometer) and are not filtered by the Earth’s atmosphere. Accounting for 90% of the UV rays reaching the Earth’s surface, they are known for their deleterious effects on our skin, namely skin aging and skin cancers.
a. UVA protection labels in the world
Several techniques, specific to each country, are used to determine the UVA protection factor. Thus, the labels can differ from country to country depending on their regulations and, unfortunately, they are not always comparable between one another, unlike SPF (see more in the 1. UVB Protection section).
Are European sunscreens better than the American ones? A study done on 20 US sunscreens marketed as protecting from UVB and UVA radiations (broadspectrum) in 2017 showed that 19 of them complied with the American federal agency FDA UVA protection rules but only 11 of them met the European Union UVA protection requirements (see just below for more information) (8). Although the study evaluated a very small number of sunscreens, EU UVA regulations seem to be stronger so that sunscreens that reach the EU market may be more protecting than those under US UVA regulations.
So, how is UVA protection labeled in the world?
In Europe, in order to indicate that a sunscreen offers a minimum UVA protection, a UVA logo is put next to the SPF number.
It means that the UVA protection factor (UVAPF) is equal at least 1/3 of the labeled SPF, or the ratio of UVAPF/SPF > 1:3.
In the United-Kingdom, the UVAPF is indicated with the Boots star rating system.
Starting from no star, meaning “No claim” on UVA protection, it can go up to 5 stars meaning “Ultra” UVA protection with a ratio UVA/UVB > 0.91, meaning that UVA and UVB protection are almost uniform.
In some Asian countries (Japan, South Korea and China), the “PA” label is used for UVA Protection. PA is followed by one (low protection) or several “+” (up to 4 for very high protection) to indicate the UVA protection factor of the sunscreen.
PA measure is based on the Persistent Pigment Darkening (PPD) method (see below for further information).
PPD factor is also available on several European sunscreen brands like La Roche-Posay or Bioderma.
PA and PPD numbers are correlated:
|PA++++||PPD 16+||Very high|
- In the USA, a product also protecting from UVA radiation can be classified as broadspectrum (UVA and UVB protection) if it contains SPF 15 or higher. Those with SPF 2 to 14 cannot state the label (7).
b. UVA protection meaning
As mentioned above, there are several techniques measuring the UVA protection factor (UVAPF) of a sunscreen:
In vivo protocols, like the one based on the Persistent Pigment Darkening (PPD) method developed in Japan. PPD is a tanning occurring between 2h and 24 hours after UVA exposure (for more of the effects of sun on the skin, click here).
It is based on the ratio of the minimal persistent pigment darkening dose on protected skin to the minimal persistent pigment darkening dose on unprotected skin of the same subject:
UVAPF = MPPDD on protected skin / MPPDD on unprotected skin
with (MPPDD = minimal persistent pigment darkening dose) (5).
- In vitro methods, like the COLIPA technique, are based on the measurement of the UV transmission through a layer of sunscreen applied onto a UV transparent support.
F.A.Q. / Myths debunked
SPF 50 twice as protective as SPF 30
This is something I have recently heard even though dermatologists usually say the opposite. I do agree with the latter and this is actually easily explained because the statement is based on a false interpretation of simple mathematics.
Here is the false reasoning:
While SPF 50 blocks 98% of UVB rays, SPF 30 blocks 96,7%. That means that 2% of UVB rays are not filtered by the SPF 50, and 3,4% for the SPF 30.
Then, if we compare the percentage of UVB rays that is not filtered, we can see that 3,4% is almost twice as much as 2%, meaning that SPF 50 would give almost twice as much UVB protection than SPF 30.
Actually, this is far from being as positive, and the correct statement would rather be:
- if we look at the amount of UVB rays that are not stopped by the SPF 30, the SPF 50 blocks almost 50% more.
Another correct interpretation would be:
- if we look at the amount of UVB rays that are not stopped by the SPF 50, almost twice as much are not filtered by the SPF 30.
Anyways, the correct statements are less impressive than the false one.
Finally, I’d like to emphasize that this kind of misinterpretations also occur in other science areas, like pharmacology, where industrials may conclude that their medicine will diminish XX disease by YY%. Here is an amazing video that talks about that kind of fallacies in cholesterol, it’s long and a little bit technique but I strongly suggest you see the video until the end. You can agree with the speaker or not but you have to reckon that pharmaceuticals love to manipulate numbers.
If you were lucky to try various sunscreens, do you prefer European, Asian or American ones? Leave a comment below!