Biology counts in loving relationships

When it comes to a healthy relationship, some biological facts can help you build one. Here's what to know before you dive fully into a relationship:

1. Love is all chemicals. When in love, your brain pumps out the love-potion ingredient dopamine (the addictive substance that sugar, sleep and tobacco also release) and increases the release of serotonin, the euphoria hormone. You also get a surge of the hormone oxytocin, which promotes a feeling of togetherness. The trouble? You develop a tolerance to dopamine over time, and the chemical tide that drives humans to stick together starts to recede as well. Relationships can lose some of their luster, which is why they need to move from being purely romantic to a deeper level of lifelong bonding.

2. Tears are good. When he or she says the L word or pops the question, go ahead and tear up. It's good for you. Emotional tears do more than keep the Kleenex folks in business. They also carry stress hormones and are a way of getting rid of them.

3. Till death do you part. When it comes to longevity, a committed relationship or marriage helps you, especially if you're male. It can reduce guys' risk of an early death by as much as 30 percent; women's risk by 20 percent. Why? Men need confidants; women already have them. But for both, less-risky behaviors follow marriage. Guys report losing the time used for risky behaviors to "honey do" lists; women lose it to writing such lists.