I seem to be having a senior moment! We're U.S. citizens travelling through JFK en route to Rome. I'm running low on a particular skin care product and thought I'd pick it up in the duty-free shop in JFK. But is it only duty-free for non-U.S. citizens? I've never really thought about it. We usually do our obligatory stroll through the shops in other countries before returning home. Please advise this very old 57 year old!