I live in Mumbai, and right now, the city is HOT. It doesn't help that I have a really low tolerance for sunshine as well as heat. To add to the irritation, people keep recommending various types of sunscreen, which is one of the many things associated with ameliorating the effects of this kind of weather. Sunscreen is used to protect the skin against sunburn by absorbing some of the ultra violet (UV) rays that would otherwise come in direct contact with our skin. The Wikipedia page on sunscreen says that using sunscreen also helps to prevent some types of skin cancer.
But what if the very thing that's supposed to prevent cancer may be causing it?
Retinyl Palmitate is a chemical added to many sunscreen brands available in the market. It is used to improve the appearance of skin by reducing dry and damaged skin. In 2010, the American Academy of Dermatology stated that retinyl palmitate does not cause cancer, However, in 2012, the US National Toxicology Program (NTP) published a study on the effect of retinyl palmitate on mice. The study found that the chemical increased the photo-carcinogenicity (cancer causing activity) of ultra violet light.
If you can find a sunscreen without retinyl palmitate in it, buy it.
Another study, conducted by the Cosmetic Ingredient Review (CIR), published its report in 2013. The study notes that retinoids readily penetrate the skin and goes on to state that repeated oral doses of retinyl palmitate were potentially toxic to rats at the sub cellular level. However, the study found that retinoid and its esters were not toxic in human subjects, and that the results of the animal studies were mixed.
From the research done so far, it appears that retinyl palmitate may be carcinogenic for animals. There is no conclusive published evidence pointing to it being a carcinogen for humans.
I think there should be some more testing done to be absolutely sure, especially since sunscreen is such a commonly used product. Till then, if you can find a sunscreen without retinyl palmitate in it, buy it.