Typically listed as Citrus grandis (grapefruit) peel extract on ingredient lists, the peel from this fruit is loaded with a class of ingredients known as furanocoumarins and coumarins, which are primarily responsible for what’s known as a phototoxic reaction that occurs when skin is exposed to the sun. Low amounts of this ingredients aren’t likely to be problematic, but watch out if it’s listed toward the beginning to middle of an ingredient list, especially if the product in question has a telltale grapefruit scent.
References for this information:
Food and Chemical Toxicology, March 2012, pages 756-60
Journal of Agricultural and Food Chemistry, December 2005, pages 9,790-9,794 and November 2013, pages 10,677-10,684