Pain is caused by specialized nerve endings called nociceptors detecting something potentially harmful, whether that’s heat, pressure, a chemical irritant, or tissue damage. These sensors trigger electrical signals that travel through your nerves to your spinal cord and up to your brain, where the sensation is processed as pain. But this straightforward pathway is only part of the story. Pain can also arise from nerve damage, changes in how your brain processes signals, inflammation, psychological factors, and even your genetics.
How Your Body Detects and Signals Pain
Your body is equipped with millions of nociceptors, nerve endings scattered throughout your skin, muscles, joints, and organs. These sensors respond to specific threats. Some activate in response to heat, others to intense pressure, and others to chemicals released by damaged cells. When a nociceptor detects something harmful, tiny channels on its surface open, allowing charged particles to rush in. This creates an electrical impulse.
That impulse travels along nerve fibers toward your spinal cord, where it gets relayed upward to the brain. The speed depends on the type of nerve fiber involved. Some fibers are wrapped in an insulating sheath that lets signals travel fast, producing the sharp, immediate pain you feel when you stub your toe. Other fibers are thinner and uninsulated, carrying the slower, duller ache that follows a few seconds later.
Once the signal reaches your brain, it’s processed across a network of regions sometimes called the “pain matrix.” One subdivision handles the sensory side of pain: where it is, how intense it feels, and what kind of sensation it produces. Another subdivision handles the emotional response: how unpleasant the pain feels and how urgently your body wants to escape it. This is why pain is never purely physical. The same injury can feel worse when you’re anxious or exhausted, because the emotional processing centers are already activated.
Three Main Types of Pain
Not all pain works the same way, and the cause determines the category it falls into.
Nociceptive pain is the most straightforward type. It comes from actual or threatened damage to your body’s tissues, things like a broken bone, a burn, a surgical incision, or joint inflammation from arthritis. The pain is usually well-localized, meaning you can point to where it hurts. Medical tests can typically identify tissue damage that matches the pain you’re experiencing.
Neuropathic pain comes from damage or disease in the nervous system itself. Instead of nerves reporting on a problem elsewhere, the nerves are the problem. Common causes include diabetes (which damages small nerve fibers over time), compressed nerves like carpal tunnel syndrome or sciatica, viral infections like shingles and HIV, physical trauma, neurotoxic chemicals, and tumors pressing on nerves. Neuropathic pain often comes with other sensory symptoms like pins and needles, numbness, or muscle weakness. One of its frustrating features is that sensory hypersensitivity can persist long after the original cause has resolved, because the nervous system has been fundamentally altered by the damage.
Nociplastic pain is the newest recognized category and the hardest to pin down. It arises from changes in how the nervous system processes pain signals, without clear evidence of tissue damage or nerve injury. Conditions like fibromyalgia, chronic low back pain, and whiplash-associated disorders fall into this category. People with nociplastic pain often experience widespread pain that doesn’t follow a predictable nerve distribution, along with fatigue, sleep problems, and difficulty concentrating. Diagnostic tests may show some abnormalities, but they don’t fully explain the level of pain the person experiences.
How Inflammation Amplifies Pain
When tissue is injured, the damaged cells and immune cells flooding the area release a cocktail of chemical messengers: prostaglandins, bradykinin, cytokines, and other compounds. These chemicals don’t just signal existing damage. They actively sensitize nearby nociceptors, lowering the threshold for activation. A stimulus that wouldn’t normally hurt, like light pressure on a bruise, suddenly becomes painful because the nociceptors in that area are now on a hair trigger.
This is why anti-inflammatory medications work for many types of pain. They interrupt the production of these sensitizing chemicals, particularly prostaglandins, reducing both swelling and the heightened sensitivity that comes with it. It also explains why inflamed areas are tender to the touch even when the original injury isn’t being disturbed.
Why Pain Shows Up in the Wrong Place
Sometimes you feel pain in a location far from the actual source of the problem. This is called referred pain, and it happens because nerves from different parts of your body converge on the same relay neurons in your spinal cord. Your brain receives the signal but can’t always distinguish which branch it came from, like crossed telephone lines.
The classic example is a heart attack causing pain in the left arm, jaw, or shoulder rather than the chest. But referred pain patterns are common throughout the body. Problems in the cervical spine can produce headaches or shoulder pain. Lumbar spine issues can cause pain in the buttocks, groin, thigh, or even below the knee. Knowing these patterns matters because the location where you feel pain isn’t always the location that needs treatment.
Psychological Factors That Change Pain Perception
Pain is not “all in your head,” but what’s happening in your head profoundly shapes how much pain you experience. Depression, anxiety, and chronic stress are among the most potent predictors of whether acute pain transitions into chronic pain. The relationship runs both directions: developing a persistent pain condition substantially increases your vulnerability to mood disorders, and existing mood disorders amplify pain.
One of the best-studied psychological contributors is catastrophizing, a pattern of magnifying pain sensations, ruminating on them, and feeling helpless to manage them. This isn’t a character flaw. Brain imaging studies show that people who catastrophize more have measurably different activity in pain-processing regions. In people with chronic low back pain, catastrophizing is linked to abnormal connectivity in the amygdala, a brain region central to threat processing. In fibromyalgia patients, those with the highest levels of catastrophizing show reduced connectivity in the brain’s built-in pain-dampening circuits.
Anxiety also heightens pain sensitivity and has been proposed as one reason women and men sometimes experience different levels of pain from the same stimulus. These psychological factors don’t replace physical causes of pain. They layer on top of them, turning the volume up or down on signals that are already there.
Genetics and Pain Sensitivity
Your genes influence how sensitive you are to pain. The most dramatic example involves a gene called SCN9A, which provides instructions for building a specific sodium channel in pain-sensing nerves. Different mutations in this single gene can produce opposite extremes. An inactivating mutation, one that shuts the channel down, can cause congenital insensitivity to pain, a rare condition where a person literally cannot feel physical pain. An activating mutation in the same gene causes hypersensitivity, where ordinary stimuli produce intense pain.
In one documented case, an 11-month-old boy with one SCN9A mutation was completely insensitive to pain, while his mother carried a different mutation on the same gene and experienced hypersensitivity. Most people fall between these extremes, but natural genetic variation in pain-related channels and receptors helps explain why two people with identical injuries can report very different levels of pain.
How Widespread Chronic Pain Is
Pain that persists beyond normal healing time is staggeringly common. In 2023, 24.3% of U.S. adults reported chronic pain, and 8.5% experienced high-impact chronic pain that frequently limited their ability to work or carry out daily activities. That means roughly one in four adults lives with ongoing pain, and about one in three of those people finds it significantly disruptive to their life.
There is no objective blood test or scan that measures pain. Clinical assessment still relies on subjective tools like the numerical rating scale, where you rate your pain from 0 to 10, or the visual analog scale, where you mark a point on a 10-centimeter line. These scales have been in use since the 1950s and remain the standard because pain is inherently personal. Two people rating their pain as a 7 may be experiencing very different things, but these tools give clinicians a consistent way to track whether your pain is improving or worsening over time.