Scientists have warned that some sunscreens can become toxic over time - producing a chemical that can cause cancer.
US and French scientists studied a number of brand-name sun lotions containing a chemical called octocrylene.
They found that over time the chemical can break down and produce a compound called benozophrene, which can cause skin and liver cancers.
Scientists want the chemical banned, reports The Mirror.
Their study has been published in the journal Chemical Research in Toxicology using brand-name sunscreen bought from shops in the USA and France.
Scientists artificially aged the products.
Speaking to France Info about the study Dr Didier Stien, one of the authors, said: "When it is on the skin, benzophenone can induce dermatitis. It can cause cancer, especially liver cancer.
"It is a molecule that affects thyroid function and disrupts the development of reproductive organs.
"To our knowledge in the scientific literature and in general, no one [before this study] had demonstrated that octocrylene degrades into benzophenone."
In the study's conclusion scientists said: "There is enough scientific literature to make an argument that octocrylene/benzophenone products can pose a threat to individual and public health.
"Several jurisdictions, including the Republics of Palau and the Marshall Islands as well as the U.S. Virgin Islands, have banned octocrylene in sunscreen and cosmetic products, effective in January 2020.
"It is agreeable that there needs to be more refined and rigorously produced, unbiased data regarding exposure and toxicity of both these chemicals and the products that contain them."
The Cosmetic Toiletry & Perfumery Association was reported to have said that the new study doesn't show that sunscreens containing octocrylene pose any health risk to humans, only that benzophenone impurities can exist after manufacture in sunscreen products.
Sun screen will have a number on the back of the packaging which shows how long you can use them after they are opened.
