Retinyl Palmitate
In plain terms
A storage form of vitamin A used in anti-aging skin care and some sunscreens. The open question is about using it on skin that is then exposed to sun.
What the evidence shows
Retinyl palmitate is where the evidence splits. A National Toxicology Program study applied it to hairless mice that were then exposed to UV light and found it sped the development of skin tumors, and an independent panel confirmed that reading. Dermatology researchers pushed back hard in the Journal of the American Academy of Dermatology: those mice grow tumors from UV alone within weeks, the tumor-free control cream also raised tumors, and some study arms ran backwards, so they argue the result does not carry to human skin. The EU's safety committee landed in the middle, saying the finding may point to a problem but cannot be cleanly extrapolated to people. There is no human evidence either way. The cautious read is product-specific: the question is real for a leave-on product worn in the sun, thinner for one used at night.
On the label
Listed as retinyl palmitate, vitamin A palmitate, or retinol palmitate. The concern attaches to products worn on sun-exposed skin, mainly daytime lotions and sunscreens, not to night creams.