Why Do Humans Kiss?

Pucker up! Few and far between is the person who doesn't like to kiss or be kissed (when it's consensual)...but when you really think about it, it's kind of a funny behavior! Even as a person who considers kissing one of her favorite pastimes, I admit I've never thought too long or deeply about why putting my mouth on another person brings me such joy.

I think we all know what kissing is, but just in case: kissing is the act of placing your mouth on someone or something, usually gently, sometimes repeatedly, or for an extended period. Usually, this is two people placing their lips together.

But when most other species of animals don't perform the same behavior, it begs the question, how did humans begin doing this, and why do we continue?

Evolutionary Perspective—Where did kissing come from?

It would be easy to assume that everyone kisses, but that's actually not true. Suzannah Weiss, resident sexologist for Biird and AASECT-certified sex educator, tells us that "romantic kissing is actually not universal within the human species." She notes a recent study of 168 cultures, which found romantic or sexual kissing only took place in 46 percent, and explains that "romantic and sexual kissing were more common in places with more complex cultures with multiple social classes."

Records of people kissing date back about 4500 years, to early human cuneiform writings, but scientists suspect kissing may have begun as far back as 100,000 years ago. It may have been a biological tool to suss out the immune system of a potential partner; Weiss says, "saliva contains hormones as well as information about the person's genes that indicates how compatible your immune systems are."

She explains that "there's also been research showing that societies where people wear more clothes are more likely to practice kissing. This may be because the face is the only part of the body that is exposed when the rest of the body is covered in clothes, and people are craving skin-to-skin contact."

Kissing also may have begun through our primate ancestors, as a method of transporting pre-chewed food from mother to baby. This is a habit used across many species. Babies naturally use their mouths for breastfeeding, so giving food to an infant by mouth-to-mouth could have been a natural next step as a baby moved from breast milk to food.

The act of kissing may play an important role in who we choose as partners. In addition to providing us with biological info, Weiss says that "the lips are one of the most sensitive parts of the body, so kissing someone is a way to get to know them better." Because humans have a less strong sense of smell than many other species, kissing is also a way to get close to another person and find out how your body reacts to their pheromones.

Psychological and Emotional Aspects

Known as the love hormone, oxytocin is key to helping us feel bonded to one another. Kissing may make our bodies create it, but that hasn't been proven true across all genders.

Weiss explains, "one study found that kissing increased oxytocin—a hormone involved in bonding—in men but not women." She add that "oxytocin is usually released during activities like cuddling and sex, so if kissing were combined with these activities, it would probably release oxytocin."

Even if it hasn't been proven to trigger the release of oxytocin, kissing still has psychological and emotional benefits. "It's a physically intimate activity, so it lets someone know that you have some kind of attraction or affection for them," notes Weiss.

Kissing is a way to get to know someone better, and it can be a good indicator of whether you'll be a fit for further intimacy. And even if things don't go further, kissing can be fun. It may release other happy hormones, like serotonin and dopamine, as well as lower your stress levels.

Social and Cultural Influences

Since not every culture kisses, it makes sense that not all cultures have the same habits and practices around kissing. Weiss notes that kissing rules aren't even consistent throughout the country, saying that "Even within the US, the social norms around kissing vary based on subculture."

She explains, "In religious communities, for instance, it may be expected that someone go on several dates and be committed to someone before kissing them. At places like nightclubs, raves, and bars, kissing may be a fun activity that doesn't have to lead to anything after the night is over. For some sex workers, kissing is off-limits because it is considered too emotionally intimate."

Health Benefits and Risks

Kissing is a two way street when it comes to our health, both having benefits and creating risks. Let's look at the different impacts it can have on our bodies.

On the plus side, kissing the same person over a period of time can boost both of your immune systems. "One study found that partners who frequently kissed had similar oral microbiomes, meaning that bacteria were transferred between the two mouths," says Weiss, who adds that "while this might sound like a bad thing, this includes good bacteria that help to fight off infections."

On the other hand, kissing can open us up to a host of negative bacteria and viruses, too. You can transmit germs for everything from cold sores to a cold to COVID. Illnesses such as Mononucleosis, known as the "kissing disease," can leave you incapacitated for month.

Kissing tends to be more common in societies with stronger oral hygiene. Because illnesses such as gum disease can be transferred via kissing, good oral hygiene is important so that your kissing doesn't cause anyone harm.

Personal and Intimate Relationships

Can a couple be happy together without kissing? Such a thing may be possible, but kissing certainly doesn't hurt, and it may be an indicator of relationship satisfaction. "Couples who kiss more frequently are more satisfied in their relationships," says Weiss. "In fact, kissing appears to have more of an impact on relationship satisfaction than intercourse. Couples who kiss frequently also have better sex lives," she adds.

There are many types of kisses, and they aren't all sexual. Parents kiss their children goodnight, we kiss our pets, and friends often kiss on the cheek in greeting. A kiss is a way of expressing affection, just like a hug.

And for our romantic relationships, they may be one of the keys to longevity. "If you want your relationship to last, don't forget to kiss your partner on the way out the door, when you come home, when you say goodnight or any time when it's convenient," suggests Weiss. "If you can get into the habit, you'll get to enjoy the benefits on a daily basis," she adds.

Keep in Mind

Kissing is unique to humans and to our primate cousins, who may have handed it down to us. It's something that just shy of half the human population does, mostly in areas with numerous social classes and strong oral hygiene. It's a way to express emotion, affection, and attraction, depending on the type of kiss, and it's something many people enjoy.

Kissing can boost our immune systems, but it can also put our health at risk, depending on whom we're sharing our mouths with. If kissing someone romantically, you should always get consent first, as it's a physically intimate activity. We enjoy it as people because it releases happy chemicals, help us feel bonded to one another, and may reduce stress.

Kissing is free, fun, and it helps relationships thrive—what's not to love?!