The millions of microbes exchanged in a single kiss – 02/26/2024 – Science

We can observe mouth-to-mouth contact between fish, birds and primates.

But intimate kissing, with contact between tongues and exchange of saliva, appears to be an exclusively human act and is common in more than 90% of cultures. Why?

Some authors have suggested that intimate kissing could help to value and affectively select your future partner, according to the chemical sensation produced by saliva.

Others have argued that intimate kissing evolved to protect pregnant women against dangerous uterine infections caused by viruses transmitted through saliva. Exposure to the virus before pregnancy could immunize the mother and protect the fetus.

80 million bacteria in an intimate kiss

In fact, these are mere hypotheses. We don’t know the reason why human beings kiss.

But, whether to select our partner or to immunize the future mother, there is no doubt that the countless microbes that live in our mouth play an important role.

A study published in 2014 analyzed the microbes present in the mouths of 21 couples after an experimentally controlled intimate kiss.

The researchers proved that, during the kiss, couples exchange part of the microbiota on the tongue and the other’s bacteria remain for hours in the new tenant’s saliva.

The study also concluded that the more we kiss our partner, the more similar the composition of saliva microbes will be between us. It seems obvious, but it needed to be demonstrated.

The researchers even calculated exactly how many kisses are needed to maintain the effect on the saliva microbiota: at least nine kisses a day.

But the most interesting thing is that the study authors calculated the number of bacteria we exchange in a kiss. To do this, they prepared a yogurt with previously labeled bifidobacteria and lactobacilli and gave it to one of the partners to drink.

After a passionate kiss that lasted just ten seconds, the researchers took samples from the “receiver” and calculated the number of yogurt bacteria that were passed from one to the other.

The conclusion was that, in an intimate kiss lasting just ten seconds, we are capable of exchanging around 80 million bacteria. In other words, with a single kiss, we exchange not only all of our love, but also something as intimate as several million bacteria.

The oral microbiome

The oral microbiome designates the community of microorganisms that live in the oral cavity (mouth, tongue, gums and throat).

It includes thousands of different species of bacteria, viruses, fungi and other single-celled organisms, which form a complex and dynamic ecosystem.

More than 700 different bacterial species have been identified. Most of them have beneficial effects, such as digesting certain nutrients, protecting against invading pathogens or regulating the local immune system.

A few are responsible for oral diseases — such as tooth decay, periodontal disease, halitosis (bad breath), oral candidiasis, etc. — and non-oral diseases — cardiovascular, diabetes and respiratory diseases.

The presence of some oral pathogens, such as the bacteria Porphyromonas gingivaliswhich causes chronic periodontitis, which is a risk factor for the formation of amyloid plaques, cognitive deterioration and dementia, typical of Alzheimer’s disease.

Kisses can transmit herpes

The microorganisms exchanged during kissing are not necessarily harmful.

In most cases, this exchange does not pose a significant health risk, as long as people have good general and oral health. But there are several infectious diseases that can be transmitted through kissing.

Herpes is a type of virus that can be easily transmitted through saliva.

Infectious mononucleosis (known as kissing disease), for example, is caused by the Epstein-Barr virus. It is a very common disease among teenagers and young adults.

Its symptoms include fever, sore throat, extreme fatigue, and swollen lymph nodes.

Simple or cold sores are transmitted through direct contact, including kissing. Its symptoms include painful blisters around the lips or in the mouth.

And genital herpes, although it is most commonly transmitted through sexual contact, can also be transmitted through kissing if there are active lesions in the mouth or around the lips.

Another type of herpes that can be transmitted through saliva is cytomegalovirus. In most cases, it does not cause serious symptoms, but it can pose a risk to people with compromised immunity or pregnant women, as it can cause very serious complications during pregnancy.

This form of transmission explains why the number of people who have antibodies against this type of herpes (the prevalence) is so high. More than 70% of the population, for example, have had contact with the Epstein-Barr virus throughout their lives.

Cavities, pharyngitis and flu

There are many other pathogens that can be transmitted through kissing if saliva is exchanged.

Among them, some bacteria such as Streptococcus mutans or Streptococcus pyogenes They cause cavities, throat infections and pharyngitis. But there are also bacteria associated with periodontal disease, such as Porphyromonas gingivalis.

And, of course, there are viruses that cause respiratory infections, such as the flu, respiratory syncytial virus and other common cold viruses.

Kissing can also transmit some types of papillomavirus and even fungi, such as yeast. Candida albicanswhich causes candidiasis.

Oral hygiene for healthy kissing

Diet, oral hygiene, smoking and alcohol consumption, use of antibiotics and other medications, genetics and other underlying medical conditions influence the composition and health of the oral microbiota.

Maintaining a healthy balance of the oral microbiota is essential to prevent diseases and their transmission through kissing. This involves frequent and adequate brushing of the teeth and tongue, combined with the use of dental floss and mouthwash — the latter, in moderation.

Furthermore, visiting the dentist regularly, limiting excessive sugar consumption and avoiding smoking are the best ways to keep your mouth healthy.

And, if we’re healthy, we don’t need to worry about sharing our microbes.

_{This article was originally published on the academic news website The Conversation and is republished under a Creative Commons license. Read the original Spanish version here.}