We’ve found that the protection offered by popular water-resistant sun creams plummets in conditions that replicate the sea and fast-moving water.
We tested water-resistance claims made by two popular sun creams and found that the sun protection factor (SPF) dropped by up to 59% after 40 minutes in salt water.
Water-resistance claims are made on the majority of sun protection products, yet our findings expose serious flaws in the current testing regime.
As well as looking into water-resistance claims, we checked the SPF and UVA of 15 popular sun creams.
Head straight to our Best Buy sun creams page to find out which sun creams will keep you protected in the sun without leaving your skin feeling sticky or greasy.
How we tested sun cream water-resistance claims
Sun cream water-resistance is tested using an industry guideline that involves human volunteers being immersed in a bath of water. They do two stints of 20 minutes, broken up by 15 minutes during which they air-dry – no towelling or patting is allowed.
The sunscreen’s SPF is compared before and after these two stints. The guideline requires the use of tap water in a bath, which continuously circulates to simulate ‘moderate activity’.
The guideline also allows for the product’s SPF to drop by up to 50% after immersion.
We decided to try a more realistic test. It still took place in controlled conditions, but we used chlorinated water to mimic a pool and salt water to emulate the sea. We also added a third scenario using tap water that was moving more than required by the guideline.
What we found
We tested two popular sun creams and found that, in the main, they weren’t as water-resistant in our more realistic conditions as they were in gently moving tap water.
One of the sun creams tested saw its SPF drop by 59% in salt water and moving water. In tap water, one product’s SPF fell by 21%, and the other by 40%. SPFs dropped by more than a third in chlorinated water. See the results in our graphic below.
You may already be surprised that you could buy an SPF30 sun cream that drops to SPF15 after immersion in tap water and that it would be acceptable under the guidelines. But our results suggest its SPF after immersion would be even lower if you went into the sea, moving water or chlorinated water.
Unacceptable sun cream guidelines
In reality, there’s no way to know from looking at the label of your sun cream what SPF you’ll end up with after going into the sea or pool.
These hidden differences between products would be less of an issue if the UK had stricter water-resistance requirements, as there are in Australia and the US. There, the labelled SPF of a sun cream must be the SPF it provides after immersion (in tap water).
We think that the current requirements around water-resistance claims are unrealistic to the point of being meaningless. You could rely on a product to provide a level of protection that it’s incapable of delivering, putting you at risk in the sun.
Nikki Stopford, Which? director of research and publishing, said: ‘Our research shows water-resistant sun creams don’t live up to their claims when subjected to rigorous tests – raising serious questions about the current guidelines.
‘With 15,400 new cases of melanoma each year, manufacturers should be required to robustly test their products and make only claims that can be relied on, ensuring holidaymakers know they can trust their sun cream to protect them.’