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"O" is for oxytocin

Oxytocin is a chemical that calms and bonds couples together by promoting intimacy.

"It is what hugging, kissing and touching are made of," says Fisher, a visiting research associate at Rutgers University in New Brunswick, NJ.

Oxytocin levels also rise in new moms, promoting milk production and bonding with babies.

So, if you feel the urge for a stay-at-home movie night to cuddle with your beau, it may be oxytocin at work.

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