Language is saturated with touch metaphors. We call emotions “feelings”; we are “touched”; problems are “thorny” or “sticky”; sensitive people are “touchy.” A toccata is a musical composition intended to showcase touch technique. The exclamation touché acknowledges a fencing strike. A touchstone was originally used to test metals. The Latin phrase noli me tangere, literally “don’t touch me” (70), derives from Jesus’s purported words to Mary Magdalen after the Resurrection and has become an expression meaning “don’t meddle or interfere” (70). We call concrete reality “tangible.” Touch is a primary way we understand experience.

Touch is essential for infant development. Ackerman recounts massaging a premature infant in a hospital incubator. Massaged babies gain weight up to 50% faster than unmassaged babies. They are more alert and discharged sooner. Saul Schanberg’s Duke experiments found that rat pups separated from mothers stopped growing; growth resumed only with the mother’s return or with very heavy stroking simulating the mother’s tongue—gentle stroking didn’t work. This mirrors the rare phenomenon of psychosocial short stature (PSS), in which children experiencing severe and consistent emotional neglect or distress sometimes stop growing, with normal growth resuming upon transfer to a safer and more nurturing environment.

Touch deprivation in monkeys leads to psychological distress and brain damage. When mothers are absent, infants lower food needs to conserve energy; if the mothers fail to return, this adaptation stunts growth. For human infants, touch signals safety. Even inanimate stimulation, like that from a lamb’s-wool blanket, helps.

As the oldest, most immediate sense, touch is an urgent alarm system. The skin has diverse receptors for tickling, itching, and pressure, but the brain avoids overload through adaptation. Though a sweater may feel scratchy when first put on, we soon stop noticing it until something changes. Some deep receptors in joints and tendons never adapt; without them, we’d lose balance. Losing the sense of touch through anesthesia or illness can be disorienting, blurring the self/external boundary.

Various nerve receptors convert mechanical energy into electrical signals. Meissner’s corpuscles, in hairless areas like fingertips (9,000 per square inch) and genitals, respond to light touch and low-frequency vibrations. Pacinian corpuscles, deeper near joints and in genitals, react to pressure and high-frequency vibrations. Merkel’s disks register continuous pressure; Ruffini endings sense deep pressure. Free nerve endings respond more slowly. Together, this network perceives everything from a caress to violin vibrations.

Hair is a cultural symbol as well as a touch organ. In nearly all cultures, hair signifies identity. Biologically, head hair may have evolved to protect the skull, but all body hair functions to extend the sense of touch. Each of the body’s approximately 5 million hairs grows from a follicle with nerve endings. Hairy skin is thinner and more sensitive—the slightest hair movement signals the brain. This makes hair an early-warning system for the body. Some animals have vibrissae, or whiskers—long hairs attached to highly sensitive clusters of nerve endings that aid in navigation.

Temperature perception is based on change, as Ackerman herself noticed when she placed one hand in hot water and the other in cold, then both in warm: The “hot” hand felt cold and the “cold” hand felt hot. Humans have distinct receptors for hot and cold, with cold receptors more numerous and closer to the surface, especially on the face, making us more sensitive to cold—an important trait since humans lack the thick fur found in many other mammal species. We shiver to warm ourselves and sweat to cool ourselves. Warm-bloodedness allowed ancestors to migrate and adapt to diverse climates.

Touch collaborates with sight to produce a three-dimensional understanding of the world, allowing us to infer what something feels like—whether it is hard or soft, heavy or light, hot or cold, by looking at it. Painters and sculptors use tangible media to produce visual effects. Historian Svetlana Alper observes that the Dutch painter Rembrandt van Rijn used thick, high-relief paint to reflect light in a way that unites “the visible and the substantial” (95), letting viewers almost feel texture. Proprioceptors inform the brain about body position, creating an often-distorted mental map in which hands, head, and mouth feel disproportionately large due to nerve density. This touch-based sense of physical reality makes art and surgery possible.

Ackerman visits the Touch Dome at San Francisco’s Exploratorium, a maze navigated in total darkness. Walls feel soft, floors slope, hands plunge into dry beans or grasp rope hammocks. A brush feels alien. The darkness induces claustrophobia and panic; one must trust touch through slides and up unseen handholds. A final ramp returns to bright light after the intense expedition into pure touch.

Many animals are masters of touch. Sponges and tapeworms rely on it as their primary sense. Nocturnal or underground creatures like moles have exceptional touch. Cockroaches use cerci to detect vibrations; alligators engage in stroking courtship; sea turtles feel through shells. Helmut Tributsch of the Free University of Berlin suggests that some animals can predict earthquakes because their dry skin and fur sense the static electricity from electromagnetic disturbances preceding seismic activity.

Tattooing is an ancient art—the skin as canvas for expression, magic, and identity, dating from Neolithic farmers to ancient Egypt and Tahiti. The Maori developed moko; Japanese full-body irezumi is a serious folk art. Photographer Sandi Fellman notes that tattoos embody “beauty created through brutal means” (100). Inks can be poisonous, and fully tattooed skin can’t breathe properly. In Japan, some individuals with masterpieces donate their skin to museums; Tokyo University has 300 such skins.

Pain is subjective and shaped by mental state. In the 1962 film Lawrence of Arabia, protagonist T. E. Lawrence (based on the real-life author of the autobiography Seven Pillars of Wisdom) the protagonist holds his hand in a flame, explaining that he can make the pain bearable by not fearing it. Soldiers ignore wounds by focusing on survival; religious martyrs endure pain through spiritual purpose. Cultures use painful initiations like the Sioux sun dance. People endure leg waxing or sports pain. This pain differs from torture because it is chosen; the context of choice makes the pain less distressing. “Referred pain” appears elsewhere than its source; amputees feel “phantom-limb pain.”

Ackerman considers the many ways people try to relieve pain. Anesthetics block pain signals; these include illicit substances like cocaine as well as pharmaceuticals. Endorphins are natural anesthetics produced by the body in response to aerobic exercise, relaxation, hypnosis, acupuncture, or even placebo. Aspirin inhibits pain receptors at injury sites. “Lateral inhibition” creates sensory confusion—rubbing near a stubbed toe overwhelms pain signals. This sensory confusion may explain why mild pain feels pleasurable during sex—a brain receiving strong pleasure signals may construe pain as pleasure. Endorphin levels rise in pregnancy, preparing for childbirth.

Pain’s biological purpose is warning. Damaged tissue releases prostaglandins, stimulating nerves to signal the brain. Acute pain forces immobilization for healing. The pattern theory holds that different nerve impulse combinations create sharp, burning, or aching sensations at different speeds. The body responds fully—pupils dilate, blood pressure rises, sweating—responses shared with anger and fear, reinforcing pain’s emotional component.

Kissing is a form of intimate touch with complex origins. Some anthropologists say it evolved from the practice of smelling faces to gauge health. Desmond Morris calls it a “Relic Gesture” from when mothers chewed food before passing it lip-to-lip. We kiss dice for luck, icons for reverence, and dying lips in the Roman custom of capturing souls. Using “X” for kisses stems from a medieval custom in which those who could not read or write would sign documents with a cross for “St. Andrew’s mark,” then kiss it. Ackerman states that according to some anthropologists, lips flushed from kissing evoke female genitalia during arousal.

Ackerman discusses the extraordinary complexity and versatility of the human hand. The hand is an instrument of both action and perception—Kant called it “the visible part of the brain” (116). Hands build, comfort, and gesture. Holding hands initiates romance, comforts the sick, and lowers blood pressure. Blind hairstylists cut by touch; people read Braille. Robotic hands struggle to match this precision. Fingerprints are unique, used since ancient China as a method of identification. The handshake originated as proof of being unarmed. The hand often symbolizes the whole person.

In a physically distant society, people seek “professional touchers”—doctors, hairdressers, massage therapists, tailors. Doctor visits are often driven by desire to be touched. Massage techniques include Swedish, Japanese shiatsu, and reflexology. Loving touch has health benefits: Rabbits that were regularly petted had 50% lower arteriosclerosis rates on the same high-cholesterol diet. Heart attack patients with pets had higher survival rates regardless of marriage status. In a “nontactile society,” we turn to animals for touch.

Every culture develops unspoken rules around touch. Ackerman states that in Fiji, touching another person’s hair without consent is considered as offensive as touching someone’s genitals without consent. Women touch other women’s hair and faces more than men touch the hair and faces of other men. Higher-status people are more likely to initiate physical contact with lower-status people, while lower-status wait for permission.

Even fleeting, unnoticed touch impacts mood. At Purdue, library patrons briefly touched by a librarian reported feeling happier, without consciously registering the touch. Waitresses who touched diners received larger tips. People were more likely to return money “lost” in phone booths when researchers lightly touched them. This subconscious response likely stems from infant experiences where touch meant safety, love, and well-being.