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Diving into the world of water-resistant sunscreens

If you saw the feature on BBC Morning Live today (27 June 2022) about water-resistant sunscreens, you might be wondering how the 'water-resistant' claim on your sunscreen bottle has been tested and what this really means for the protection you will receive.

At CTPA, we’ve gathered together the answers to the common questions we are asked about water-resistant sunscreens.

Dr Emma Meredith, Director-General of CTPA and a Pharmacist says:
“In the UK, if a sunscreen says that it is water resistant or very water resistant, it will have been tested using an internationally recognised, validated method.  The method has been developed over many years by suncare experts from around the world to make sure it gives reliable and consistent results. 
“A robust body of evidence is required to substantiate sun protection claims and these in-depth testing regimes by manufacturers must be taken into account if any ad-hoc testing of a product is to be carried out or any challenge of an on-pack claim is made.
“The recognised industry test method assesses and compares the SPF before and after being in a whirlpool with fast moving water.  This determines that the sunscreen will not be completely washed off, even under tough water conditions.
“It’s really important to stress that no sunscreen is 100% waterproof or 100% effective at blocking UV rays – and these claims must not be made.  This is why the product label will tell us to reapply our sunscreens, even water-resistant products, after we have been swimming or towelling dry.”
 

What is the difference between water-resistant sunscreens and non water-resistant sunscreens?

Water-resistant, or very water-resistant, sunscreens are designed to stick to the skin for longer.  There are various ways in which these products are designed; for example, some products incorporate ingredients that help the UV filters penetrate the upper layers of the skin where they are protected more from being washed off.  Others rely on the technique of binding the UV filter tightly to the skin, using water and abrasion-resistant material.

As with all sunscreens, it is important to follow the instructions for application and use; and remember not to use sunscreen to stay longer in the sun.

What’s the difference between ’water-resistant’ and ‘very water-resistant’ sunscreens?

The difference between these two claims relates to how long the sunscreen was tested for in the water during the internationally recognised water resistance test.  For both claims, the sunscreen must retain at least 50% of its original SPF after going through the testing process.

In the test, the same amount of sunscreen is applied to each volunteer in the same way. For ‘water-resistant’ sunscreens, the volunteers then are in a whirlpool bath for 40 minutes and for ‘very water-resistant sunscreens’, they are in the whirlpool for 80 minutes in total.  The water in the whirlpool must be constantly swirling to represent the volunteers moving around in the water, as if in a pool or the sea.

How much protection is lost after being in the water?

To pass the test, a product must retain at least 50% of the initial SPF value after immersion in water. In fact, an SPF 30 product will stop approximately 96% of UV rays reaching the skin and after robust water resistance testing the product will still filter out at least 93% of the sun's UV rays. However, a non water-resistant product could be washed off the skin completely meaning no protection from UV rays (until reapplication).

Why doesn’t the industry test method use chlorinated water or salt water to better represent a pool or the sea?

The official testing process uses specially standardised tap water and this is a harsher solvent than salt or chlorinated water. This is because purer water has more ability to act as a solvent and remove sunscreens from the skin than water which is already heavily saturated with chemicals such as salt or chlorine.  Also, it is very important to ensure that water used in the testing is standardised, for reliable results.  Chlorinated water or sea water are not standardised.

More help and advice for staying safe in the sun

For more helpful advice about how to stay sunsafe, visit our page how do sunscreens work?  You will find videos from Dr Anjali Mahto, Consultant Dermatologist and British Skin Foundation spokesperson, as well as a factsheet answering the most frequent questions CTPA receives about suncare.

Finally, don’t miss our joint blog with British Skin Foundation Chief Executive Matthew Patey OBE: It’s official! Suncream is a Self-Esteem Essential. So how should you apply it to get the best protection?

 

27 June 2022

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