Given that so many consumers slap on sunscreen as a precursor to diving into the ocean, or a hotel pool on holiday, water resistance is a highly in-demand attribute when it comes to sun protection.
But, until recently, there was no universal immersion procedure to ascertain water resistance.
Both the US Food and Drug Agency (FDA) and Cosmetics Europe have their own methods, but these subtly differ and there is little way of telling whether these differences have an effect on the results or not.
Therefore, the testing of sunscreen water resistance and its calculation were both ripe candidates for standardised procedures under the International Organization for Standardization (ISO).
ISO 16217, which specifies a procedure of water immersion for the in vivo determination of the water resistance of sunscreen products, and ISO 18861, specifying a procedure for evaluating the water resistance retention percentage, were both published this year.
Dr Marc Pissavini, Research Director at Coty and convenor of ISO’s Working Group 7 (WG7: Sun Protection Test Methods) tells Cosmetics Business that work on the procedure for immersion, ISO 16217, began in Paris back in 2015, with work on the second standard, ISO 18861, the calculation of the percentage of water resistance, commencing roughly a year later.
“We first needed to make the immersion process and then to calculate, so the calculation was launched a little bit after,” he says.
“Why we needed two methods is due to the regulations,” he explains. “Water resistancy is regulated in different ways all over the world. What they have in common is the immersion procedure: everybody should use the same procedure to put people into the water and measure the SPF.
“After that, what you do with this measurement depends on the country. In the US, Australia or New Zealand, to measure the water resistancy, you need to put volunteers in a bath, but you only need to know the SPF after the bath, because the water resistancy is the SPF you have after 40 minutes or 80 minutes in that bath. So, if you start with an SPF50 and you finish with an SPF25, in the US, you will only have SPF25. What is important is to know how to put the volunteer into the bath and all the procedures.”
On the other hand, “in Europe, you would do exactly the same: you’d put the volunteer into the bath and follow the ISO 16217, but the calculation is completely different”.
In Europe and UK, as well as in countries including Japan, China, Korea, Taiwan, Mercosur and South Africa, what is measured is the percentage difference of the SPF before and after the bath.
“In Europe, if after the bath you have more than 50% of your original SPF – so, using the same example, if you start with SPF50 and you have more than SPF25 after the bath – you can claim you are water resistant,” Pissavini explains.
From ideation to publication
Pissavini is keen to stress that ISO does not exist to validate methods. Nor was the aim for ISOs 16217 and 18861 to start from scratch. Rather it was “to find an agreement, a harmonisation” between the FDA and Cosmetics Europe methods.
“We refine two methods that already exist and ISO is there to find a compromise and consistencies between both and publish it. The mistake would be to think that ISO is there to undertake research and to validate a method: it’s not.
“Also, you are not obliged to use ISO methods. It’s a standard where if you want it, you can use it. You don’t have to use water resistancy 16217 to test water resistancy. But most countries will now prefer these official methods to something that you’ve come up with yourself, as it’s much easier to compare ISO methods versus another method. And even if it is not mandatory, most countries and organisations, CROs [contract research organisations], for example, will use it.”
The approximately five-year process of taking these standards to publication took place in multiple stages, as Pissavini elaborates.
“The first one [stage] is a New Work Item Proposal. Beforehand, there is an earlier stage that is not mandatory called a Preliminary Work Item, which is really a reflection on the subject during which experts working on the standard will assess whether we have enough data, if the method is advanced enough to present it as a new subject at ISO level, etc.
“However, the first mandatory level of ISO is the New Work Item Proposal. The committee votes on this and, once we have a New Work Item Proposal Working Draft, it is at this stage that experts from around the world discuss all the technical points. There can be as many as six or seven Working Drafts.”
Once WG7’s experts – which includes upwards of 40 individuals representing countries from across the Americas, Europe, Africa, the Middle East, Asia and Australia – think that they have made enough improvements to the method, it can then be presented as a Committee Draft.
“We present this to the Technical Committee, which is made up of countries,” says Dr Pissavini. “It’s not experts who vote, it’s countries – France, the UK, the US, Japan, etc. The Committee normally follows what the Working Group proposed, but adds some comments. These are not necessarily technical but more global comments, such as ‘it is acceptable?’, ‘is it easy to follow?’, ‘does it need to be modified because it’s confusing?’
“With this Committee Draft, if it is accepted, you respond to the comments and see that all of these are answered. Then you jump to the DIS, which is a Draft International Standard.
“You draft it again and resend it to the Technical Committee; you may receive some comments and, as soon as you answer these, you jump to the FDIS, which is the Final Draft International Standard. Here you may have editorial comments, but there cannot be any technical comments at the FDIS stage.”
Finally comes publication, whereby the FDIS is validated by the Technical Committee then published by the ISO Central Secretariat in ISO format and translated into French.
Ordinarily, the shortest timeframe to progress through all required stages is three years, but, as Pissavini notes, “most of the time you have ring tests to validate some point, or you need to run experiments and that requires around one year”, so the full process more frequently takes four years.
ISO 16217 & 18861: The specifics
As mentioned earlier, when it comes to the water immersion procedure for determining the water resistance of sunscreen in vivo, historically two methods have commonly been used with the US opting for the FDA method and Europe using the Cosmetics Europe (formerly Colipa) method. Pissavini notes: “These two methods were similar but with some differences… however, they were similar enough to propose an ISO method combining both.”
The publication of ISO 16217 clarifies and harmonises several potential variables, for example, the definition of the spa, which was inconsistent between the FDA and Cosmetics Europe versions. “We decided to harmonise and to give a definition of the spa,” says Pissavini.
Other inconsistencies between the pre-existing methods that have been harmonised in ISO 16217 include the sample location – essentially where the sunscreen is placed on the back of the volunteer; the subjects’ position in the spa – whether the volunteers are placed closer to the jet, or further away; and the flow measurement of water into the spa.
“Something which was very important was to define the water,” adds Pissavini. “Because you can have different types of water – salt water, tap water, local water. And we also define the hardness, conductivity, pH and temperature of the water. We had to define the temperature of the air outside too.”
Another aspect was providing a standardised sanitation method, which is “perhaps not very important for the SPF, but is very important for the volunteer”.
Something Pissavini highlights as being “very important” is the agitation. “Should the agitation be only made by water, or by bubbles, which is water plus air?” he asks. “This could have an effect!”
In the end, “in the ISO method, we defined that the agitation should be made only by water jets – no air. Because you can imagine that, depending on the spa used, some might have bubbles and some might not. But now it is well defined.”
Also specified within the standard is the range of the value – something incorporated into all methods – which exists to ensure CROs and test institutes complete their experiments to high enough standards. Likewise, CROs are required to use/check the standard once every two months.
Pissavini reiterates that ISO 16217 is not a “revolution”, but a “fine tune [of] the methodology to find the best compromise between the FDA and the Cosmetics Europe/Colipa methods”, which aims to “reduce all the areas that can lead to variability in the final result”.
Publishing ISO 18861 for evaluating the water resistance retention percentage was a rather simpler process.
As Pissavini explains: “You don’t have to harmonise this, as it’s the calculation of a percentage. It was quite an easy method. We had to define the range of the P2 standard, but that was the only difficultly.”
Future focus
In conjunction with publishing ISO 16217 and ISO 18861, WG7 has been developing or improving several other sun protection test methods in recent months.
One of these was a systematic review of the in vivo SPF method, which “is where we already have an ISO method [in this case published in 2010], but we’ve decided to review and update it”, which was also published this year.
“We have also had a revision of the in vitro and in vivo UVA methods, and there are two in vitro SPF methods currently in development at ISO level,” says Pissavini.
These, he says, are especially important, “as we have no alternative method for the SPF in vivo”. The standards, which are being developed in parallel, are for two different testing methods: HDRS (hybrid diffuse reflectance spectroscopy) and SPF PMMA double plate testing.
According to Pissavini, the original plan was to publish these SPF in vitro standards in 2022, but the necessity for a ring test means they may be in the pipeline for a little longer.
In the meantime, sun care manufacturers can breathe easy knowing they now have a water-tight option for assessing their products’ water resistance.
