Bad news, beauty buffs: Layering SPF make-up over sunscreen could be a dangerous mistake for your skin.

Mixing chemical sunscreen with make-ups and moisturisers that contain a zinc-based SPF make both less effective at blocking cancer-causing UVA light, a new study has found.

You should definitely still wear sunblock: A slip, slop, slap, seek and slide lifestyle is fully endorsed by TND.

But some products should not mix, according to a study by the University of Oregon and the University of Leeds published in Photochemical & Photobiological Sciences.

“We still recommend consumers use sunscreen, but suggest they should be careful to avoid mixing sunscreen with zinc oxide,” study co-author Professor Richard Blackburn from University of Leeds said.

Zinc on its own is an “effective and harmless UV blocker”, Professor Blackburn told News Medical.

But when it is mixed with other chemical sunscreen ingredients it causes both to be much less effective at sun protection.

It is possible to buy hybrid sunscreens that contain zinc as well as other sunscreen ingredients, but the research suggests these should be avoided.

And it also advises against putting make-up with an SPF (which often contains zinc) on top of a chemical sunscreen.

This is a step often recommended by beauty influencers as a way to double down on sun protection.

The researchers created five SPF15 chemical sunscreens (containing no zinc oxide) and found them to provide effective protection against UVA.

They then added 6 per cent zinc oxide to one of the mixtures, and tested all six by exposing them to UV light over two hours.

Science says sunscreen and SPF make-up do not mix. Image: TND

They found the protection offered by the cocktail of sunscreen and zinc oxide – which is similar to that provided by make-up and sunscreen – dropped by 84.3 per cent to 91.8 per cent over that time frame.

But the protection offered by the chemical sunscreen on its own only dropped by 15.8 per cent.

Yikes!

• Related: Five common sunburn myths busted

Professor Blackburn said putting on sunscreen and make-up with SPF was even worse than not wearing any, because people stay in the sun longer when they think they are protected.

His colleague, Professor James Hutchinson from the University of Oregon, told News Medical the study also found that combining zinc with other chemical sunscreen ingredients could be toxic, based on tests with zebra fish embryos.

“So not only is the lack of effective UV protection an issue, the product itself may be causing harm during use in the sun,” he said.

What can you do about it?

Professor Blackburn said the industry conducts no testing to find out how different sunscreen and UV blocking ingredients react with each other.

He and the other authors have therefore called for more stringent testing practices.

And in the meantime?

Although the risk of skin cancer is frightening, and premature ageing is less than ideal, you can take a simple step to protect yourself.

You guessed it: Check the ingredients.

Choose a make-up base that is free from zinc oxide and work in a healthy helping of sunscreen as a separate step.