Marc H. Bornstein Article

Touch – How We Enter, Understand, and Respond to Our World

You can close your eyes and try to imagine what it’s like to be blind or plug your ears and imagine what it’s like to be deaf. But it is extremely difficult to imagine what it’s like not to perceive touch. Our sense of touch is always “on”, transmitting through our skin a diverse array of sensations- a soft stroke on the arm, the sting of a bee, a cold burst of air, an irritating itch. As a scientist researching touch once mused, we cannot imagine life without the sense of touch because touch is so deeply woven into our sense of self. What do we know about touch? Here we learn about the primacy of touch among the five senses; the formative information that touch conveys; how touch works and its biology; ways we understand the world through touch; how touch shapes our emotional and social well-being; the personal and cultural meanings of touch; and the many practical and therapeutic uses of touch.

The Primacy of Touch in Development

Touch is the first sense to emerge in utero. As early as eight weeks after conception, fetuses give evidence that they sense touch on their faces and react to stimulation there; by 14 weeks, their whole bodies respond to touch. Still in the womb, the fetus begins to accumulate sensory experiences through touch, feeling the warmth and movement of amniotic fluid and the contours of their own bodies, which they actively explore. Fetuses even respond to touch from outside the womb. Between 21 and 33 weeks after conception, fetuses have been observed moving their arms, head, and mouth in response to mothers rubbing their abdomens. Immediately at birth, newborns use their sensitivity to touch around the mouth to nurse on the breast or bottle, and physical contact with their caregivers introduces newborns to the existence of the world outside themselves. While human newborns do not need to cling to their caregivers like other primates do, tightly grasping a finger placed in their hand is a universal neonatal reflex.
“To be meaningful, everything must first be sensed and perceived.”

Touch and the Other Senses Working Together

Our five senses—sight, hearing, smell, taste and touch—are our gateway to the world. To be meaningful, everything must first be sensed and perceived, and the senses naturally work together to help us comprehend and appreciate our environment. For example, we rely on sight and taste to decide if food is safe to eat, sound and sight to ascertain if a disturbance in the woods is benign or threatening, and touch and sight to determine how to grip and lift an object. Stimulation of our senses fuels our biological, cognitive, social and emotional development. However, a person can be blind or deaf or lack the senses of taste or smell and still lead a full productive life. But what if we are deprived of touch? Although it is difficult to separate the contribution of any one sense to what we perceive, this article explores the many unique contributions of touch to our development and the ways in which we understand and relate to others.

Touch Is Information

Touch conveys a wealth of information about the world, and we need touch to navigate our way around our environment. Eons ago, the Greek philosopher Aristotle wrote De anima and expressly linked tactile perception with practical intelligence; in English, to “grasp” a meaning is to understand. Through touch, we localize when and where on our skin an object makes contact and what its many different properties are–whether the object is hard or soft, rough or smooth, heavy or light, hot or cold. We even discriminate subtle differences in types of touch, a pat, a hug, a pinch, a stroke, or a tickle, to name but a few. Touch conveys both pain and pleasure, and touch is a means of communicating emotion: a gentle caress or an abrupt push inform us immediately how our partner feels. Indeed, even newborns use touch to glean information about salient properties of objects such as their texture, weight and temperature.
We sense touch primarily through our skin, the largest organ of the body, and the body’s stoutest shield and protector. Skin shuts out dangerous substances, such as pathogens, while keeping in vital body fluids. Our skin helps us maintain normal body temperature and miraculously heals itself when damaged.

More than Skin Deep: How Touch Works

The top layer of skin is called the epidermis, and just below, in the dermis, is where most touch receptors (nerve endings) are located. Touch receptors transmit tactile sensations on the skin to the brain. Not all regions of skin on the body are equally sensitive to touch. Fingertips, lips, and tongue are more sensitive than stomachs and backs: for example, we can tell the difference between two pin pricks that are only 2 mm apart on our fingertips, but cannot distinguish one from two on our lower backs unless they are 30–40 mm apart. This differential sensitivity reflects the greater concentration of touch receptors on the fingertips than on the lower back, and the number and distribution of touch receptors mean that more sensitive regions of skin are represented in greater magnitude in the parts of the brain that process touch (primarily the somatosensory cortex). Notably, tactile experience affects how parts of the body are represented in the brain. For example, playing certain string instruments, like the violin, that require continuous left-hand fingering (as the right hand holds the bow) results in greater representations of the left-hand fingers in the somatosensory cortex. Albert Einstein played the violin from a young age, and an autopsy of Einstein’s brain showed this.
Besides their number and distribution, touch receptors also come in a variety of types that signal different tactile sensations. Some receptors specialize in mechanical stimulation (like pressure, vibration and texture), others in temperature, pain, and even gentle caresses (which, as you can imagine, play a special role in our emotional well-being). Touch receptors tell us about objects we are exploring (in what's known as active or haptic touch) – for example, "this peach is soft, so it must be ripe" – just as they tell us that we are being touched (which is called passive touch)—like when someone taps our shoulder, or when our sweater feels scratchy – for example, that someone is tapping our shoulder or that our sweater is scratchy. Temperature receptors help us regulate our body temperature and warn us about things that are so hot or so cold that they may harm us. Similarly, pain receptors alert us about danger to the body’s integrity and propel us to take appropriate action–for example, to find and remove a painful splinter. Still other touch receptors reside in our muscles, joints, and tendons. These receptors convey information about our movements and body position (called kinesthetic perception). Some touch receptors carry messages to the brain only slowly, and others swiftly (such as if a flame touches our skin), some persist in signalling their sensations, and others adapt and stop signalling (we are hardly aware of the clothes continuously touching our body). Taken together, touch receptors allow us to perceive many different sensations.
“Numerous studies have examined the effects of supplemental stimulation on the development of preterm babies.”

Touch Is Rooted in Our Biology

A lot of what we know about the biology of human touch surprisingly comes from studies of “touch deprivation” in rats and monkeys and in children who have been reared in compromised situations–premature babies in incubators and children living in institutions. The animal studies have been especially revealing.
Many young animals separated from their mothers show significant developmental delays and behavioural abnormalities, but what exactly about the absence of maternal care causes those adverse effects? To find answers to this question, in the 1980s, scientists first isolated newborn rat pups from their mothers and documented the expected developmental delays. These delays were accompanied by marked changes in the pups’ biochemistry, notably the suppression of growth hormone release and protein synthesis. The question then arose: what type of stimulation would make these growth parameters return to normal? Controlling pups’ body temperature, feeding, and auditory, visual and olfactory stimulation made no difference in their growth. Deprived pups could even be returned to their litter mates and to their mothers, who had been anaesthetized to prevent maternal stimulation but not feeding, and the pups’ growth did not return to normal. The missing active ingredient turned out to be the tactile stimulation derived from mothers’ normal licking and grooming of their pups. When the researchers simulated those tactile sensations by stroking the pups with a wet paint brush at the pressure and frequency of their mothers’ licking and grooming, the growth hormone production and protein synthesis of the pups returned to normal. Loss of tactile stimulation from their mother has long-lasting effects on the pups’ physiology: pups whose mothers licked and groomed them frequently at birth responded more adaptively to stress as adult rats than pups of low licking-and-grooming mothers.
These animal studies informed our understanding about the role of touch in human development. Two situations provide “natural experiments” of what happens to human infants when deprived of touch. One is prematurity and isolation in neonatal intensive care units (NICUs), and the other is orphanage rearing. A study in the 1960s suggested that institutionalized babies provided just 20 minutes of extra tactile stimulation per day after ten weeks fared significantly better on developmental assessments. In the late 1980s, however, the world’s attention was drawn to the plight of Romanian orphans who were living in stark institutional environments deprived of normal human and environmental stimulation. These orphans showed shocking delays in long-term growth and poor socioemotional development. Of course, they lacked many types of stimulation, but because of orphanage understaffing, lack of tactile stimulation–human touch–was a prominent deprivation in these unfortunate orphans’ lives.
Highly premature babies can spend their first weeks (or even months) in incubators and thus do not experience a normal range of sensory stimulation, including touch. With advances in medical treatment, survival rates for these infants have greatly improved. However, a continuing challenge has been to ensure that preterms grow and develop normally, as many suffer significant developmental deficits.
Numerous studies have examined the effects of supplemental stimulation on the development of preterm babies. Not surprisingly, because of the relative salience of the different senses early in development (when sight and hearing are not as well-developed as touch), tactile stimulation is particularly effective in improving developmental outcomes. Following the studies of tactile stimulation of rat pups, researchers have explored whether touch, in the form of massage, combined with moving babies’ limbs, could improve outcomes for preterm babies. Indeed, preterm babies who receive supplemental tactile stimulation gain more weight than those who do not, are more active, show better performance on standardized assessments of development (including orienting, motor behaviour and regulation of state), and on average spend fewer days in hospital. These benefits remain even accounting for other stimulation, food intake, and infants’ medical status. Moreover, the effects of massage persist: when tested after 8 and 12 months, massaged infants weigh more and score better on mental and motor assessments. Similar salutary effects of touch on development have been found with typically developing babies. The “still face” is a psychological paradigm where a mother first interacts normally with her infant but then adopts a nonresponsive stance, remaining still and ceasing to interact. In this way, the still face simulates maternal deprivation by making the mother temporarily socially unavailable to the child. Normally, babies as young as two months of age become upset during the still face. Infants will display negative physiological (hormonal and cardiac) and behavioural (withdrawal, gaze aversion, self-soothing and negative arousal) responses. However, when mothers maintain a still face but continue to touch their infants, the infants cry less, display less negative arousal and self-soothing behaviour, and, notably, their negative physiological reactions are reduced.
Together, these deprivation and experimental studies demonstrate the power of touch in regulating biology and behaviour. What's more, numerous other studies have catalogued the many beneficial effects of touch on babies’ stress responses, arousal, heart rate, blood pressure, immune system and more. Nearly all around the world, parents swaddle infants as an effective means to soothe them, decrease stress, reduce heart rate and induce higher-quality sleep. Touch exerts similar soothing effects on adults. Physical contact–such as holding hands, hugging or receiving a massage from a romantic partner—before a stressful situation (e.g., public speaking) lowers blood pressure, heart rate and stress hormone levels. Volunteer “grandparents” who both received massages themselves and gave massages to infants experience less anxiety and depression, enjoy better sleep and benefit from lower levels of stress hormones. Touch has many practical and therapeutic functions that will be discussed below.
“Touch even informs how best we should grasp an object.”

Touch Affects How We Understand the World

Touch plays a crucial role in apprehending the world around us. Infants first explore the world via sensitive touch receptors in their mouths and on their tongues. Newborns turn their heads reliably toward a touch to the side of their mouth or their cheek and over the next several months eagerly explore their hands, feet, clothes and blanket with their mouths. Everyone has noticed how babies invariably bring objects in their hands to their mouths to discover their features. This hand-to-mouth coordination has even been observed in utero, such as when fetuses suck their thumbs. Newborns can already discriminate some properties of objects by touch, such as texture and weight, and by they're three to four months old, infants palpate objects in ways that conform to the object’s features–for example, by scratching a textured toy but not a soft toy. Actively manipulating an object conveys a lot of information about the object’s properties that static contact just does not deliver.
To investigate the world, adults usually use all available senses, but everyone has had opportunities to use active touch instinctively in order to search “blindly” in a pocket for keys or, hands forward, to find their way in the dark relying exclusively on touch.
Adults deploy several different tactile exploratory techniques, primarily when vision is unavailable, and each is geared to obtain a particular type of information: running a hand along the surface of an object to determine its texture; squeezing an object to determine its hardness or compliance; moving a finger along an object’s edge to determine its contour; grasping an object to determine its shape and volume; laying a hand on an object to determine its temperature; and holding an object to determine its weight. Touch even informs how best we should grasp an object. Reflect for a moment the last time you adjusted a tool in your hand to best accomplish a job. People with nerve damage in their hands frequently drop things because they lack touch receptor feedback to the brain necessary to fix their grip. As people age, their density of touch receptors and thus their tactile sensitivity declines, often making them clumsier.
“Just being touched affects how we feel.”

Touch Shapes Our Emotional and Social Well-Being

Just being touched affects how we feel. A pat on the back can make us feel relaxed and happy, but a jab in the arm can make us feel agitated and angry. Touch also affects how we feel about others. Among babies’ first social experiences is the loving touch of a caregiver. Such touches foster a sense of security and trust in the infant and a connection between infant and caregiver. “Attachment” is the term widely used to refer to the special bond formed between infants and their primary caregivers. The ethologist John Bowlby theorized that this unique bond evolved to ensure infant survival by keeping mother and helpless babe in close physical contact.
Psychologist Harry Harlow’s groundbreaking experiments with infant rhesus monkeys confirmed the importance of “contact comfort” in normal social and emotional development. Infant monkeys raised with access only to wire “surrogate” mothers, one of which was covered with terrycloth and one of which provided life-sustaining milk, spent most of their time clinging to the terrycloth mother, and only briefly visited the wire mother to nurse. Later, only the cloth mother was a source of comfort, and the monkeys used the cloth mother as a safe base to explore their environment.
Social grooming among our primate relatives (macaques and chimpanzees) brings the animals into close physical contact and occupies a significant portion of their day, maybe second only to foraging and feeding. Such touching serves several purposes: it defines and solidifies social relationships (e.g., between mother and offspring, close kin, dominant and subordinate adults, and sexual partners); it facilitates forging new relationships (e.g., chimps are more likely to share food with chimps who groomed them earlier in the day); and it assists in conflict resolution and reduction of aggression.
The socioemotional significance of touch has a lifelong effect, and researchers now refer to the skin as a “social organ.” Neuroscientists have discovered that social functions of touch are actually part of our neural wiring. For example, some mechanical skin receptors are excited specifically by stroking at a pressure and speed resembling a gentle caress, and when stimulated in that fashion generate a pleasant sensation. These receptors communicate in turn, not with the sensorimotor part of the brain, which is the terminal for other mechanical receptors, but with parts of the brain that process emotional and social information.
The pleasant sensation that comes from skin-to-skin contact promotes affiliative behavior between people that facilitates sociality. When Romeo sees Juliet for the first time, he muses to himself:
“See how she leans her cheek upon her hand. / O, that I were a glove
upon that hand / that I might touch that cheek!”
Touch is vital to trust, cooperation and group function. For example, brief celebratory touches, such as chest bumps and hand slaps, enhance individual and group performance in professional basketball players, and do so by reinforcing cooperation. Gentle touches affect social relationships in ways we are not always even conscious of. People are likely to give bigger tips, return money left behind, rate a store more highly and even spend more money if just gently touched in the course of a transaction. The slow stroking of a romantic partner, at the pressure and speed that triggers a pleasure response, can even reduce the subjective feeling of pain. Evolutionary scientists have concluded that the affective function of touch is an adaptation evolved to promote positive physical contact, such as nurturing and supportive social interaction, and so is critical to positive lifelong social relationships.
Touch communicates a wide variety of emotions—from love to anger—without any other cues, and does so just as reliably as do faces or voices. In English, such common expressions as something is “touching” or being “touched” by someone or something is a direct expression of emotion.
“Sometimes reaching out and taking someone’s hand is the beginning of a journey.”

Vera Nazarian

Science Fiction Author

Personal and Cultural Meanings of Touch

Not all forms of touch are equal. The meaning of touch is surprisingly complex, reflecting many factors such as the characteristics of the touch and our personal history, status and culture. Mechanical touch has different physical properties that result in different sensations and perceptions: the intensity of the touch (a tap versus a poke), the frequency of the touch (one pat on the back versus repeated patting), the duration of the touch (a quick hug versus prolonged contact), where on the body the touch occurs (a pinch on the cheek versus a pinch on the behind), all influence whether the touch “feels” pleasant, annoying or painful as well as whether the touch signals affection or aggression.
Who touches whom and how conveys information about the individual such as their gender and status within a society. A hug from a friend may feel pleasant, but a hug from a stranger or a boss may feel intrusive. In the West, men tend to touch women more than women touch men, and older people tend to touch younger people more than vice versa. Touches reflect status differences between groups as well as gender and age mores. How people around the world greet one another regularly involves ritualized touching. The British-American anthropologist Ashley Montagu listed a fantastic array of touch-related greeting behaviours from around the globe that included kissing (once, twice, or multiple times), nose rubbing, cheek rubbing, back slapping, hand shaking, placing the hand over the heart, head bumping, and more. Fist bumping is both a greeting and a shared celebration common today. As one philosopher observed: “Sometimes, reaching out and taking someone’s hand is the beginning of a journey.”
The socioemotional meaning of touch deeply reflects one’s culture. Different cultures follow different rules about what is an appropriate and acceptable touch versus what is taboo. Shaking hands with someone of the opposite sex may be warmly welcomed in one culture but might be considered unpleasant, unwelcome, and offensive by someone from a culture where members of the opposite sex are prohibited from touching. The frequency at which people touch each other varies across cultures and relates to other cultural customs. For example, mothers in Cameroon, where interdependence in social relationships is the norm, maintained body contact with their infants during periods of free play significantly longer than mothers in Greece, where the focus in development is on fostering interpersonal independence. Not surprisingly, some authorities have claimed that societies in which people touch each other often are more peaceful than societies characterized by little mutual touching. Clearly, what our culture teaches us about acceptable and unacceptable behavior factors in whether we touch, whom we touch, and how we interpret touching and being touched.

Practical and Therapeutic Uses of Touch

Because it is so pervasive in life and so powerful a conveyance of information and emotion, touch has an enormous variety of uses in society. As a means to allow the blind to read, Braille was developed as a system of raised dots on a page that are separated by distances that can be perceived using the pad of a finger. Machines have been designed to take advantage of tactile capabilities to help the disabled. For example, touch sensors allow the deaf/blind to operate computers, smartphones and elevators.
The therapeutic uses of touch date back millennia, and the restorative goodness of touch finds many applications today. A notable example is “kangaroo care” (named because it resembles how kangaroos carry their young), where infants clothed only in diapers are held against the bare chest of a caregiver. Kangaroo care started in Bogota, Colombia, in the 1970s to address high infection and mortality rates in hospitals due to crowding and scarcity of incubators. Mothers were encouraged to hold their babies in skin-to-skin contact for extended periods and while breastfeeding. Morbidity and mortality among the infants rapidly declined. In the years since, many studies of kangaroo care have validated its numerous, substantial and long-lasting benefits for babies and families. In low- and middle-income countries, kangaroo care has been found to reduce mortality, infections and severity of infections, and length of hospital stays, and to improve mother-infant bonding, breastfeeding and maternal satisfaction. In high-income countries, where mortality and illness are not high-risk factors, kangaroo care has been found to promote mother-infant bonding and breastfeeding. Among its reported benefits are cardiorespiratory and temperature stability, better sleep organization, improved performance on behavioural assessments, reduced adverse responses to painful procedures and an improved family environment. Little wonder that kangaroo care and other forms of skin-to-skin contact have become accepted parts of newborn care in many hospitals. Of course, skin-to-skin tactile stimulation is not the only sensation kangaroo care affords, but it is certainly a significant component.
Still other well-recognized medical applications of touch include massage therapy whose benefits (in addition to those already discussed for preterm babies) are multiple–reduction of blood pressure, anxiety, heart rate, depressive symptoms and even persistent lower back pain, to name just a few. Hippocrates, the father of medicine, has been credited with saying that “anyone wishing to study medicine must master the art of massage.”
“One touch of nature makes the whole world kin.”

Touching and Being Touched

Touch is where science meets civilization. Through the natural and medical sciences, we have come to understand much more deeply the mechanisms of action and the biochemical, biological and neurological impacts of touch. Through the social and behavioural sciences, we have come to appreciate the meaning and functions of everyday experiences of touch. Touching and being touched are so common that we readily take them for granted and may hardly think about them–except, of course, when they thrill us or when a line is crossed. Some touches are decidedly not positive. Unwanted touches, slaps, or punches are deeply problematic and have long-term problematic consequences for children and adults alike. Solitary confinement or being “out of touch” with other people is mentally damaging. As we have now learned, however, many touches are welcome, longed for, and essential in life. As William Shakespeare wrote in his play Troilus and Cressida: “One touch of nature makes the whole world kin.”

Marc H. Bornstein

Marc H. Bornstein is one of the leading experts in the field of child and youth development and in this capacity has also researched the effects of touch on human development extensively.

He holds a BA from Columbia College, MS and PhD degrees from Yale University, and honorary doctorates from the University of Padua and the University of Trento. He has published widely in experimental, methodological, comparative, developmental, and cultural science as well as neuroscience, pediatrics and aesthetics.