If you've lost that lovin' feeling, blame your neurochemistry.

Scientists have recently figured out why the sexual spark can go out; the chemical signals which make people sexy to new partners, that create that "love at first sight" feeling, only stay active for about two years.

Your relationship isn't doomed, because that hormone is replaced by oxytocin - the cuddle hormone - that gives you that warm, fuzzy feeling you need to stay together for the long term.

But if you still want that lusty hormone fix, here's how to get it:

Abstinence Makes the Heart Grow Fonder

"Put a ban on intercourse," says Debra Herbenick, a researcher at the Kinsey Institute for Research in Sex, Gender and Reproduction at Indiana University Bloomington. "What often happens in relationships is that people start skipping over the fun parts and the foreplay. By agreeing not to have sex, you take away the routine and might end up restoring the excitement of what it felt like when your relationship was new. Using this strategy, some couples who haven't had sex in 15 years have rekindled the romance in a matter of weeks."

Work Up a Sweat

When you and your lover first started dating, your brain was pumping out phenylethylamine (PEA), which pretty much drove you lovesick lustbunnies to chase each other 'round the bedroom. Now that it's been replaced by a tamer brain chemical cocktail, get your PEA fix in other ways. It's generated by exercise, for example, which may explain why people who exercise regularly report being more sexually active. (Plus, exercise acts as a stimulant, increasing blood flow and raising the level of feel-good endorphins.) PEA is also released from roses and lilies (reason enough to give her flowers, right?) and is found in trace amounts in chocolates.

Have a Dangerous Liaison

Danger is a powerful aphrodisiac. In one famous experiment, some men were told by a female assistant that they would have painful electric shocks administered. Others were told they'd feel no pain. No one, in fact, was shocked, but the men who anticipated the pain found the female assistant much more attractive than those weren't scared. Raise your adrenaline levels by adding risk to you sex life - visit a risqué shop or get busy in a semi-public place.

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