He walks you to your door, wondering how things will end. You fumble for your keys, hidden by lipstick, a wallet, and the various contents of your purse. He shifts slightly, a little nervous, and thanks you for a great time. You smile sweetly, having found your keys, looking subtly at his lips. He leans in, brushing a stray lock of hair from your cheek, and then it happens—in an instant, your lips meet his.
The experience of a fist kiss can be emotionally momentous, thanks in no small part to the chemical and biological changes occurring in the body. As one starts to kiss, the nerve endings in the lips become more sensitive. The stimulation causes these nerve endings to fire signals back to the brain’s cortex to release neurotransmitters, including dopamine, endorphins, and phenylethylamine. Dopamine is largely responsible for feelings of pleasure and motivation to engage in pleasurable activities. Endorphins, which are peptides, are known to relieve pain in the body, but they can lead to feelings of euphoria as well. Phenylethylamine, an alkaloid also found in chocolate, is thought to influence mood and attention. When these neurotransmitters are released throughout the body, they result in sensations of happiness, giddiness, and euphoria. No wonder kissing feels so good.
Meanwhile, the adrenal glands—part of the endocrine system located on top of the kidneys—are also stimulated. They are signaled to produce norepinephrine and epinephrine. These chemicals are responsible for activating the sympathetic nervous system in response to external stressors. As a result, heart rate increases, pupils dilate, blood sugar elevates, and lipids break down in preparation to release more energy. The chemicals also cause blood to move from the stomach to other muscles, including sexual organs as one becomes more aroused. Furthermore, with arousal, the hypothalamus may be stimulated to produce gonadotropin-releasing hormones, eventually leading to the production of testosterone in the testes and ovaries, which also enhances sexual desire. As the kissing intensifies, you become more excited; you feel your heart racing as you yearn for more.
As people kiss, oxytocin, which is a hormone made in the hypothalamus and released from the pituitary gland near the base of the brain, also increases. Among many other functions, oxytocin is thought to reduce stress and increase feelings of connectedness. Along with the endorphins, it is thought to influence feelings of happiness and attachment found in committed, loving relationships. Pheromones, which are chemical messages sent between members of the same species, may also play a part in human attraction. The vomeronasal organ, located between the nose and mouth, usually detects others’ pheromones. Although it is still unclear how they work, pheromones are thought to signal sexual arousal and increase attraction towards appropriate partners. You feel fantastic; the warmth and appeal for your date grows beyond your imagination and leaves you feeling closer than ever.
He squeezes you tightly one last time before you begin to back away, neither of you aware of the internal changes and reactions that have just occurred in your bodies. You barely remember the keys in your hand, as you thank him for a wonderful time. He smiles at you happily, already daydreaming about the few moments before. You unlock the door and slip inside, thinking, “There’s nothing like a first kiss.”