Even if you consider yourself a complete perfume idiot -- even if you couldn't tell Chanel No. 5 from Shalimar if your life depended on it -- you probably know that perfumes are made of more than one scent. You won't find too many perfumes (at least none you'd want to actually buy) that consist entirely of sandalwood oil, for example, or patchouli.

You might not know, however, exactly how a fragrance is constructed. All the different scents aren't thrown together willy-nilly into a big pot and then funneled into dainty glass bottles. No, there's a science -- an extremely exact science -- to it, one that some people spend large chunks of their lives perfecting. We can't go into all the details in this article, but here's the general idea: All perfumes, even the most basic ones, blend three scents, or "notes."

The top note, which might last a couple of hours, is your first impression of the perfume. The heart notes are the foundation of the fragrance, and this lasts a couple of hours longer. So by the time only the base notes are left to linger, the perfume could (and probably will) smell 180 degrees different than it did at first.

There's really no limit to how many ingredients can go into each note. The specific arrangement of the base note, heart note and top note -- and their reaction with your skin -- is what gives a perfume its own personality and causes its aroma to subtly change.

On the next page we'll give you more insight into top notes.