Kissing is a complex social behavior that varies widely between cultures and individuals. It develops from a combination of biological, psychological, and social factors. Biologically, kissing increases heart rate and the release of hormones like oxytocin, dopamine, and serotonin that promote bonding. Historically, kissing has been depicted in art since the 19th century and was categorized by the Romans into different types of kisses. The practice and meaning of kissing depends greatly on the surrounding cultural and historical context.