Sure, you've rounded the sexual bases in your relationship many, many times, but that doesn't mean you should skip over first. The problem is, as many couples become more serious, their makeout sessions start dwindling until suddenly they're not kissing as passionately—or as often—as they used to. 

Here's why: "Kissing evolved as a way to assess a potential partner's compatibility because it exchanges a host of information about health and hormonal status," says Gordon Gallup, Ph.D., a professor of psychology at the University of Albany. "Yet, once people choose a partner, kissing may die down because there's no longer a need to gauge each other's DNA." 

But even if you know he's The One (or could be!), you owe it to your sex life to keep smooching. "Saliva contains the sex hormone testosterone, which triggers libido," says biological anthropologist Helen Fisher, Ph.D., a research professor at Rutgers University in New Jersey. "So the more time you spend kissing, the more primed you'll be for sex, resulting in a more intense sexual experience." Try these tips to heat things back up. 

Add Novelty
You have four lips and two tongues between you, so be creative. William Cane, author of The Art of Kissing, recommends a move he calls "lip-o-suction." To try it, softly kiss his upper lip while he lightly chews and sucks your lower lip, then switch, explains Cane. No doubt he will try to slip you the tongue, but don't let him...yet. Wait until he's all riled up, then allow your tongues to wander over each other's teeth, inner cheeks, and gums. The alternating sensations of the hard, smooth tooth enamel and the inside of a soft, moist mouth will awaken your senses. 

Sweeten the Deal
Mickey Rourke's character in the movie 9 1/2 Weeks had the right idea when he fed Kim Basinger juicy strawberries during their naked romp. Eat one before making out; strawberries activate the sweetness receptors in your mouth, so when you kiss, your sense of taste will go into overdrive, says Krista Bloom, Ph.D., author of The Ultimate Compatibility Quiz. 

Create Spine-Tingling Chills
Swipe on mint lip balm before planting one on him to engage touch, taste, and smell. "Menthol triggers the body's cold receptors, and when that's combined with your warm breath, you'll feel a tingly sensation from your lips straight down to your genitals," says sexologist Ava Cadell, Ph.D. You can get a similar sensory effect by taking a swig of champagne or seltzer. The bubbles will tickle, tingle, and then evaporate. Just one note: Menthol can irritate sensitive skin below the belt, so if you'll be paying each other some oral attention later, make sure you both wash your lips and rinse out your mouths first. 

Rough It Up
A small dose of pain will take an ordinary smooch to extraordinary heights. "The feel-good endorphins your body releases as you kiss and become more aroused are a natural pain reliever," says Sadie Allison, D.H.S., author ofRide 'Em Cowgirl: Sex Position Secrets for Better Bucking. "Plus, when you apply firm touch to the body, you force more blood to rush to those areas, heightening the responsiveness of your skin receptors." So wrap your hand around the nape of his neck and gently pull him toward you, maintaining eye contact. Then, as your lips meet, slowly get aggressive, letting your passion build naturally. "The idea is to use subtle force. Lightly pull at his bottom lip with your teeth, rake your fingernails down the side of his neck and back, and tug his hair after warming him up with some soft, sensual kissing," says Allison. 

Bring Him to the Brink
For the most erotic type of kiss (with the least erotic-sounding name), try "facial intercourse," suggests Cadell. This type of smooch mimics sex from foreplay to penetration, beginning with a tongue exploration inside your man's mouth. "Rub your tongues together in small and large circles, then dart them in and out of your mouths, as if you were having intercourse," she says. "You can also take turns wrapping your lips around each other's tongues and sucking passionately, alternating between slow and quick movements, much like oral sex."