I’ve written about this before, but I think it bears repeating. Nowadays we are more and more concerned about the contents of our food, whether it has been sprayed by insecticide and the new worry, whether is contains an e-coli virus. In English we talk about preservatives in this context, so it is natural to assume that the Spanish equivalent would be “preservativo”.
Not so … “preservativos” are what you (or some people anyway!) get from those little dispenser machines outside the chemists. Be warned! I have talked to a class of Spanish teenagers about “preservativos” in food – an experience not to be repeated!