Ah, love. In the heady days of a mutual crush, pulses race, knees go weak, and heads reel. So strong are these feelings, they've launched a thousand songs and poems.

But it's more than just a metaphor. Love does indeed impact our bodies in measurable ways. You feel different and are different. Read on to find out what researchers have discovered about this thing called love.


Addicted to love
Dopamine is the brain's pleasure chemical. It plays a role in gambling, drug use, and, well, love. When we fall in love, dopamine is released, making couples feel elated and energetic about each other.

"That someone takes on special meaning to you and you focus on this individual because the dopamine system has been activated," says Helen Fisher, a biological anthropologist. "It is what triggers very goal oriented behavior, where no one else matters but your new partner."

Dopamine can be present in both early-stage and long-term romantic love, she says.

'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, N.J.

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.

Testosterone takes off
Although testosterone is thought of as a macho hormone, it helps stoke the fire in both sexes. "It is just one of the many pieces for romantic love," says Fisher. "Sex can drive up your testosterone levels."

Men naturally have higher testosterone levels and trace amounts in saliva. One theory says that when people lock lips, the transfer of this hormone could increase sexual desire in a partner.

Tongue tied?
Another possible ingredient in the love potion is norepinephrine (it's still being studied). This stress hormone increases the heart rate, and may be the reason you feel hot and flustered when that special person notices you.

Fisher says it might also be responsible for that butterflies-in-your-stomach sensation. "It can cause that awkward feeling," she says. "Sweaty palms, dry mouth, fumbling words."

Love connection
The major histocompatibility complex (MHC) is a set of genes that controls cell-surface molecules, which the body uses to tell self from foreign invaders.

Our bodies exude MHC levels through sweat and body odor, as well as saliva. There are a wide variety of MHC types, but they tend to more closely match in people who are related.

Based on scent and taste, studies suggest we can pick up on MHC levels in other people, and it's thought that the more you differ in MHC, the stronger the attraction.

Follow your nose
The saying is usually love at first sight, but your nose plays a part too. Pheromones, which are chemical messengers, are theorized—but not proven—to play a part in human sexual attraction. (They're major players in insect behavior.)

Fisher says she isn't a fan of the pheromone theory, but believes smell is a part of love.

"Once you fall for someone, their smell can be a powerful thing," says Fisher. "Women will wear their boyfriends T-shirts and throughout tales in history men have held on to their lover's handkerchief."

This article originally appeared on Health.com.