You've been there: your best friend wears a certain perfume that smells amazing on her, but the second it hits your skin your stomach churns. What's the deal? "Body chemistry has everything to do with how fragrances smell," Anne Nelson Sanford, cocreator of Lurk fragrances, says. "It depends on the pH of your skin." And since you and your friend aren't the same person, perfumes are going to smell differently on you two. But it's not just body chemistry that affects the way perfume smells. Find out what else changes the way your perfume smells when you keep reading.