In pictures: 15 facts about kissing that will surprise you
The word kiss originates from the Old English term 'cyssan', which means 'to kiss' in turn from 'coss' ("a kiss").
Researchers believe that kissing evolved from the practice of premastication also known as kiss-feeding, a process used by mothers to feed their infants by passing chewed food to their babies' mouths.
Affectionate mouth-to-mouth kissing was first described in the Hindu epic, the "Mahabharata".
Several academics and scholars are of the opinion that, kissing spread slowly to other parts of the world after Alexander the Great and his army conquered parts of Punjab in northern India in 326 B.C.
According to recent studies, the average person spends around 336 hours kissing in a lifetime.
As kisses weren't shown in Indian cinema for many years, the first open-mouthed smooch they saw was in a little-known English-language film in 1926.
Kissers should beware as a single snog can contain up to 278 types of bacteria, some of which may carry diseases, while a passionate peck can raise hormone levels enough to shorten your life by a full minute.
The first openly gay big-screen kiss came in the 1922 film Manslaughter, which featured two lesbian women kissing.
The most kisses seen in a film was 191 - Don Juan, in 1926 - while the longest-ever kiss lasted a breathtaking (and strength-sapping) 31 hours and 30 minutes.
In 2011, a Thai couple locked lips for 46 hours, 24 minutes and nine seconds to celebrate Valentine's Day. The previous record of just over 32 hours was set in 2009 by a couple in Germany, according to Guinness World Records.
Recent studies suggest that increasing the frequency of kissing in marital and cohabiting relationships results in a reduction of perceived stress, an increase in relationship satisfaction, and a lowering of cholesterol levels.
Kissing can also cause the adrenal glands to secrete epinephrine and norepinephrine (adrenaline and noradrenaline) into the blood, thereby causing an adrenaline rush, which has a beneficial impact on the cardiovascular system because the heart pumps faster.
A passionate kiss generally burns up to 2–3 calories per minute.
Kissing is a complex behavior that requires significant muscular coordination involving a total of 34 facial muscles and 112 postural muscles. The most important muscle involved is the orbicularis oris muscle, which is used to pucker the lips and informally known as the kissing muscle.