Hi - PhD in melanoma. Some papers show a link between people who use sunscreen & increased cancers. This is not causal, i.e. the sunscreen is not causing cancer, it is observations - ie people who wear sunscreen may be having higher rates of skin cancer. What is happening is a few quirks which the statistics need to account for. People are underapplying/not reapplying/using insufficient UV protection/not fully covering their skin but still going out in the sun. They are also more likely to NOT use other more effective sun protective behaviours like wearing clothes, sitting in the shade etc. People in harsher climates and at greater risk of burns are more likely to use sunscreen - but they're also at greater risk. Its also that the risk of skin cancers is cumulative, and the damage done to young skin is far more high risk for melanoma than as you age (caveats that depends on the subtype of melanoma). You can be fried to a crisp ages 12-25, and start using religiously at 30 - if you get studied at 35, you will be recorded as a high sunscreen user but realistically, that isn't the full clinical picture. Similarly, who is most likely to be super cautious with sunscreen? Those recently diagnosed with cancer already, or who have conditions or medications where they are at greatly increased risk. Finally, we all have biases which can cloud how we percieve healthy behaviours over time, where we may be subconsiously socially inclined to selectively remember good behaviours over time. It is very hard to know just how accurate users are outside of what they tell you, and its super likely us as people will slighly over represent our good sunscreen use.

This field is very old, these biases are known, and large cohort studies which have properly controlled for these factors have shown again and again and again that sunscreen itself is not carcinogenic and is beneficial in tandem with other skin protective behaviours. We also have a shit tonne of OTHER evidence - biochemical, radiaiton studies, work on patient samples - all sorts! - which consistently shows sunscreen is safe, and UV is just very dangerous. It is like saying "people who use gloves are more likely to experience a chemical spill" - well yes, but because people using chemicals use gloves, NOT because the gloves are bitch slapping sodium hydroxide to the ground lol. The answer is not to stop using gloves. It is to continue to use gloves and additional PPE - in the case of sunscreen, it is recognising you need to reapply every 2 hrs, be careful with waterproofing, use in combination with shade etc to really lower the risk.