cited from https://www.psychologytoday.com/basics/oxytocin
What is Oxytocin?
Oxytocin is a powerful hormone. When we hug or kiss a loved one, oxytocin levels drive up. It also acts as a neurotransmitter in the brain. In fact, the hormone plays a huge role inpair bonding. Prairie voles, one of nature's most monogamous species, produce oxytocin in spades. This hormone is also greatly stimulated during sex, birth, breast feeding—the list goes on.