Mouth to mouth kissing is a behaviour seen in almost 90% of all human cultures, and used as a non-verbal communication of intimacy, affection and love. For centuries scientists have been pondering the origins of this primitive behaviour and whether it has a functional purpose in our lives.
So where did kissing come from? Apparently, the earliest record of kissing dates back to 1500 BC where references to ‘drinking moisture from the lips’ were mentioned in Northern Indian Vedic texts. What’s more is that the Kamusutra, which details over 30 different types of kissing, dates as far back as the 6th century AD. According to Philematologists (scientists that study kissing!), it is hypothesized that kissing evolved from an early primitive behaviour known as the ’maternal permastication of food’, which quite literally involved the mouth to mouth contact between a mother and child in the exchange of food during infancy. Despite kissing not being a necessary requirement for successful reproduction, it is hypothesized that sexual kissing may have evolved from this display of care and affection, to eventually promote pair bonding and to facilitate in assessing mate suitability. While mouth to mouth contact is seen in numerous animals as part of courtship rituals, sexual kissing appears to be unique to our species, and may explain why our inverted shaped lips appear to differ from all other animals, almost as if they were shaped for such a purpose!
Despite the seemingly unhygienic nature of kissing, and the fact that it does expose us to the risk of oral infection, this primitive affectionate behaviour represents an evolutionary benefit in conferring protection from diseases that may impose more serious consequences. Mouth to mouth contact essentially exposes each person to the diseases of the other, which while not sounding particularly clean, can actually enhance our own immunological control of exposure to infection. According to research by the journal ‘Medical Hypotheses’, kissing represents an evolutionary conserved biological behaviour that boosts our immunity to the Human Cytomegalovirus (HCMV). HCMV is a particularly nasty type of the Herpes virus that can carry a significant teratogenic risk for women i.e. it can have a severe impact on the their unborn children during development, if primary infection occurs during pregnancy. The risks to infected neotates include a number of serious development abnormalities such as enlargement of the liver and spleen, as well as a number of neurodevelopmental disorders including abnormal brain growth, seizures, cerebral palsy and mental retardation. For 30% of infected fetuses the disease is lethal, and as a result, numerous pregnancies are terminated if infection is detected. HCMV is transmitted in saliva, urine and semen. As the disease is only symptomatic during the active phase, it is not an easy virus to readily detect and thus avoid, especially when trying to conceive. In order to avoid infection of the HCMV during pregnancy, researchers have hypothesized that kissing has evolved to allow women to control the time of inoculation, and that transmission of small amounts of the virus at this point through the saliva will confer immunity to the condition and prevent the presentation of symptoms.
It is now understood that affectionate behaviour has a number of stress-relieving effects. As stress, mainly via the ‘stress hormone’ cortisol, has a number of detrimental influences on our endocrine, nervous and immune systems, kissing may in fact confer significant health benefits by reducing these effects. Interestingly, not only does kissing improve our mood and thus reduce stress levels, it may actually act to reduce a number of parameters that are exacerbated by stress. Stress can elevate blood cholesterol levels, in one manner through stimulating the release of cortisol. Chronic elevation of cholesterol can lead to the build up of plaques and the clogging of arteries that may eventually trigger the development of coronary heart disease. It was identified that an increase in kissing behaviour between marital couples during a 6-week trial period lead to a decrease in blood cholesterol levels, and thus an improvement of blood lipid composition and reduced risk of cardiovascular complications.
Surprisingly, kissing may also enhance your dental health! While it wouldn’t be recommended as a replacement for brushing your teeth in the morning, the extra saliva generated during a kiss washes bacteria off your teeth, and as a result encourages the break down of oral plaque. Kissing also burns calories and raises your metabolism too. According to the research, a vigorous kiss burns up to two calories a minute and can almost double your metabolic rate (the rate at which you can process food). And it makes sense, as kissing involves the coordinated contraction of more than 30 facial muscles, the constant exercise improves muscular tone in the face. One in particular, known as the orbicularis oris muscle, is used to pucker the lips and has been informally termed the kissing muscle. It has been suggested that the regular contraction of these muscles during a passionate kiss enhances muscle strength and tone and may actually contribute to maintaining a youthful complexion. So a passionate kiss may be the perfect non-surgical remedy for keeping your face young!
On what is seemingly quite an obvious level, kissing enhances the release of endorphins in the brain and has a number of other emotional health boosting benefits that improve mood and mental well-being, reduces depression and stress, and most importantly promotes intimacy and pair bonding. So not that we need an excuse, but it seems that appreciating the importance of a good kiss will benefit your health and mental well-being in more ways than one, and if not for anything else, then use it as a happiness boost!
For more information see;
Hendrie CA and Brewer G (2010): Kissing as an Evolutionary Adaptation to Protect Against Human Cytomegalovirus-like teratogenesis. Medical Hypotheses 74: 222-224.
Floyd K, Boren JP, Hannawa AF, Hesse C, McEwan B and Veksler AE (2009): Kissing in Marital and Cohabiting Relationships: Effects on Blood Lipids, Stress, and Relationship Satisfaction. Western Journal of Communication 73: 113-133.