1. Love is like chocolate. There's a reason newlyweds can't get enough of each other: Love is a kind of chemical addiction, says Helen Fisher, Ph.D., an anthropologist at Rutgers University, who scours MRI bran scans for the secrets of love. Falling in love activates the "pleasure" centers of the brain and increases production of the feel-good chemical dopamine, which plays a key role in addictions. And eating chocolate affects the same brain regions, which is why it's hard to stop at one piece of candy. How? A surge of dopamine is part of a chemical cocktail that boosts your mood and energy levels, and sharpens your ability to focus on -- read: obsess about -- your sweetie. Is it possible to feel that rush even after you've been married for years? Absolutely. "Novelty drives up dopamine too," says Fisher. So you can get a boost from trying something new in the bedroom or ordering takeout Thai food instead of your usual pizza.

2. Your nose knows he's the one. Did you just know he was the man for you? Thank your sense of smell. "Women can sniff out a partner who is a good genetic match for having kids," says James V. Kohl, a clinical laboratory scientist and coauthor of "The Scent of Eros: Mysteries of Odor in Human Sexuality." Kohl and other smell researchers have found that women are instinctively drawn to the scent of men who are genetically different from them, which is a good thing. "If you choose a partner whose genes are too similar to yours, your children are at an increased risk for health problems," he explains. What draws you to one guy over another is his pheromones, unique chemical by-products of hormone production. Women are especially good at detecting pheromones during ovulation, when our sense of smell is strongest. When you like what you smell, your estrogen levels go up, sparking desire.

3. Marriage doesn't make you crazy -- it keeps you sane. Forget the popular image of the married couple driving each other nuts. "Studies show that getting married improves mental health and decreases depression," says Linda Waite, Ph.D., a sociologist at the University of Chicago and coauthor of "The Case for Marriage." In fact, one study found that people who've never walked down the aisle are more likely to be admitted to a psychiatric facility. "Many women gain a deep satisfaction from the intimacy found in marriage," says Scott Haltzman, M.D., clinical assistant professor of psychiatry at Brown University. "That sense of belonging bolsters their sense of self-worth and purpose," enhancing their mental stability.

4. Marriage keeps you healthy, too. Saying "I do" isn't just good for your mind. Married people -- even those in less-than-perfect unions -- are physically healthier than those people who aren't married. They have stronger immune systems, better resistance to viruses such as colds and flus, fewer long-term illnesses and disabilities, fewer hospitalizations, better survival rates for the illnesses they do get, and longer life spans -- by up to eight years! Interestingly, though, when it comes to preventing heart disease and strokes, studies have found that being hitched helps only if your relationship is happy. "Your heart knows whether your marriage is good or not," notes Haltzman.

5. It's better to be hitched than rich. What makes people happiest? Being wealthy helps, but it's a solid marriage that seems to rank highest on the smile scale. According to a Dartmouth study, having a good marriage is equal to the satisfaction gained from earning an extra $100,000 a year. So you really can be rich in love.

6. A dad's love runs deep, too. If you think there's nothing more amazing than a dad nuzzling his newborn or walking hand-in-hand with his grade-schooler, you're right: "When a man holds his child, he experiences a very distinct and powerful hormone change," explains Fisher. "We see this in humans and in animals." His levels of testosterone -- a.k.a. the aggression hormone -- go down, while his levels of the connecting hormones oxytocin and vasopressin increase, which triggers bonding by making him crave closeness.

These physiological changes have been around since the dawn of time, but today's fathers are much more hands-on, which actually deepens their attachment to their kids as they grow. A recent survey found that 93 percent of dads with school-age children hug them at least once a week, which is up from 90 percent a decade ago; 60 percent hug them every day. Hugs have a biological benefit, too: They reduce heart rate, blood pressure, and stress hormones, and boost the immune system -- of the hugger and the huggee.

7. Puppy love is powerful. Many studies have found that pets can lower blood pressure and ease loneliness. Now, new research from the University of Missouri-Columbia suggests the hormonal changes that occur when people and dogs interact could counteract depression and stress disorders, too. Just a few minutes of petting Fido causes a release of happy hormones like serotonin and oxytocin, while reducing stress hormone levels. You don't even need your own pooch to reap the benefits, says researcher Rebecca Johnson: "You get them when you pet any dog."

8. Getting busy keeps you young. People who have physical intimacy four to five times a week look more than 10 years younger than those who have physical intimacy twice a week, according to a 10-year study of 3,500 people at the Royal Edinburgh Hospital in Scotland. Why? Experts aren't sure, but they do know from previous research that the testosterone released during climax helps men maintain muscle mass. As for women, the estrogen surge experienced during physical intimacy may make our hair shinier and skin smoother, both signs of youth.

9. Chick flicks turn him on. Your man may not realize it, and he certainly won't admit it, but this romantic genre is more likely to inspire sensual feelings in him than his favorite action flick, according to a study at the University of Michigan. Researchers there found that watching a romantic movie can boost a guy's progesterone levels by more than 10 percent, increasing his lovey-dovey feelings. Still, getting him to sit through "Bridget Jones's Diary" on DVD may be tricky -- even on Valentine's Day. So rent a chick flick with romantic leanings cloaked in a tough-guy hero. For that, "Casablanca" never fails.

10. Love is a wonder drug. No, really. As if there weren't enough reasons to put on some Barry White, here's more good news about physical intimacy. During a sensual encounter, your body pumps out 200 percent more endorphins (those feel-good chemicals responsible for a runner's high), according to a recent Johns Hopkins University study. Other research has found that physical intimacy relieves headaches and zaps mild depression instantly. The adrenaline released can act as a natural antihistamine, clearing up the winter snuffles. One study even showed it was 10 times more effective than Valium at giving people a calm, contented feeling. No Rx required!