Black lace. White satin. Red velvet. Or for some, even just a plain pair of cotton underwear. Any of these bring up images or memories?

Before the 20th century, most undergarments were used as shapewear (think corsets). Being squeezed half to death just wasn't that sexy, so the concept of alluring, sexually suggestive underwear is actually quite recent. It appeared in the late 19th century when women started wearing less constraining "dessous."

Since then, our lingerie has become a kind of fashion statement: are you sporty, classic, trendy? Do you prefer lace or satin? Sheer or opaque? Do you wait with bated breath for the next Victoria’s Secret fashion show? Do you choose your underwear for comfort or looks?

"Intimate apparel" was worth $10.9 billion in sales in the U.S. in 2009, a figure that has been growing each year. It is also estimated that each woman spends up to $360 per year on underthings. Curiously, it's single women who tend to spend the most.

So, what makes us so willing to spend money on garments that so very few people will see? Here’s my take on it.

It Makes Us Feel Sexy

Whether you're gettin' some or not, what you're wearing under your clothes is like a dirty little secret that you can take everywhere with you. Passersby in the street won’t know that you’re wearing your cute pink polka dot bra and thong kit, but you do. And you feel all the sexier for it.

It’s easy to indulge in fantasies of spontaneous sex in the elevator when we wear lingerie. Plus, when we spend the day fantasizing about hot sex, we get home ready for some action!

I dare you to wear your black lace set and not feel a titillating sexiness. It’s perfect when you need to boost your confidence for a hot date. (Manufacturers are increasingly making sexy getups for plus-sized women as well. Read more in Worried About Weight? How to Have Spectacular Sex Anyway.)

It Makes for Great Foreplay

Sometimes, sex is meant to be savored. Lingerie adds some visual interest and provides a bit of an extra challenge in terms of removing it. And if you're wearing lingerie that you love, it gives you the chance to stand back and be admired. There is pleasure in seeing and being seen, and lingerie adds to that pleasure. You could even let your partner take some hot photos for later.

Lingerie also encourages partners to take their time, to enjoy the view and to extend the sensual moment of sliding a pair of lace panties down a hot pair of legs. It's a way of building arousal and sexual tension, which can lead to some pretty explosive sex. Think of it as an intimate strip tease: exotic dancers never take off everything at once! (Learn more about exotic dancing from someone who's been there in Exotic Dancers: They Aren't Who You Think They Are.)

It's a Special, Private Showing

Many women love wearing lingerie for themselves, but we also like to do it for our partners. Nothings says "I'm thinking about you" like a sexy outfit. What better way to put you both in the mood?

Sometimes, lingerie can be about showing off your best assets and making your partner crazy for you. Surprise them when they undress you, or start something by walking into the bedroom in a see-through lace chemise or a sexy bra, thong and garters with your favorite high heels.

It Makes for Great Role-Play

If your usual underwear mode is "as comfortable as possible", then lingerie can put you into a different kind of mood. You can play the sultry mistress, the mysterious spy or the experienced call girl.

Wear plain white panties under a plaid skirt to play the innocent schoolgirl, or black lace under a red dress to play the irresistible femme fatale. Take that French maid costume out of the closet and clean up your Master’s drawers. Lingerie provides infinite possibilities for imaginative role-play!

It Sends a Message

Everything about lingerie says "special," whether it’s just you feeling especially sexy getting to work, or your partner feeling especially loved because you put on their favorite nightie. In fact, the kind of lingerie you wear can tell a lot about your personality in bed. A tank and panties says "fun and playful" while a clingy lace baby doll tells a whole different story.

So, what sort of story are you hoping to play out tonight? Either way, you're probably both in for a happy ending.