Benzophenone
In plain terms
A fragrance ingredient and product-protecting UV absorber, and a different chemical from oxybenzone (benzophenone-3, the sunscreen filter). It is flagged by several agencies as a possible carcinogen, which is why it is worth skipping where you can.
What the evidence shows
Benzophenone is a compound with a sweet floral smell, used as a fragrance ingredient and as a UV absorber that protects a product and its packaging from light, in things like lotions, soaps, and nail polish. It is worth saying up front that this is not oxybenzone: oxybenzone is benzophenone-3, a sunscreen filter, while plain benzophenone is a separate chemical with its own profile. The concern is cancer. The International Agency for Research on Cancer lists it as possibly carcinogenic to humans, based on animal studies showing liver and kidney tumors, and the US National Toxicology Program reported similar findings; California lists it under Proposition 65 for cancer with no safe level set for personal-care products, and the FDA removed its approval for use in food. The honest limits: the cancer evidence is from animals, human proof is not established, and benzophenone is on the EU list of endocrine-disruptor candidates but is not strongly hormone-active on its own. Even so, when an ingredient draws a possible-carcinogen call from IARC, a Proposition 65 cancer listing, and a lost food approval, and it is only there to absorb light or add scent, skipping it costs little. It can also form in sunscreens over time as the filter octocrylene breaks down, which is a separate route worth knowing.
On the label
Listed as benzophenone, which is not the same as benzophenone-3 (oxybenzone) or benzophenone-4 (sulisobenzone). It shows up in fragranced lotions, soaps, and nail products. Easy to avoid by choosing fragrance-free or benzophenone-free products.