Touch “is the core of sentience, the foundation for communication with the world around us, and probably the single sense that is as old as life itself.” Indeed, touch is “the most intimate of senses” .
From infancy to adolescence and through all of life, interpersonal haptic behavior plays a vital role in our lives. Human haptic behavior extends far beyond the sensory world to every aspect of the social world. Interpersonal touch expresses warmth, affection, intimacy, immediacy, and love [2–4] but can also threaten and even injure. Haptic behavior also plays a central role in promoting health and happiness throughout the lifespan [1, 5–8]. Within social relationships, touch differs based on sex differences and relational stage. Cultural differences in touch also exist. Finally, sometimes touch is avoided, either because people have a predisposition that causes them to be touch avoidant, or because there is a taboo against touch. These issues are explored in this chapter, starting with the social significance of touch.
The social significance of touch
Experts believe that touch is the first sense to develop and the last sense to depart when we die . From the time babies are in the womb, tactile stimulation plays a critical role in human development. Touch provides a channel for connecting to others and learning about the world. As Moszkowski and Stack  noted, “touch is an important modality through which infants and mothers communicate; it is also a vital means through which infants self-regulate and explore their surroundings” (p. 307). People who are deaf or blind are able to adapt to the loss of these senses and lead healthy, productive, and socially meaningful lives, but “an existence devoid of tactile sensation is another matter; sustained physical contact with other humans is a prerequisite for healthy relationships and successful engagement with the rest of one’s environment” (p. 28) . Children who are deprived of contact with others are disadvantaged socially, emotionally, cognitively, and physically.