Why does one person describe an injury as unbearable while another seems to cope with the same injury relatively well? And why can two people with apparently similar injuries sometimes recover at very different speeds? The answer is that pain is not simply a measure of how much tissue has been damaged. It is a complex experience created by the nervous system and influenced by biological, psychological and social factors.

When tissue is injured, specialised nerve endings detect potentially harmful stimuli and send signals through peripheral nerves and the spinal cord towards the brain. The brain then interprets these signals as pain. But the intensity of that experience can be influenced by everything from genetics and age to existing illness, stress, expectations and social support.

The International Association for the Study of Pain (IASP) describes pain as an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage. It also emphasises that pain is a personal experience influenced by biological, psychological and social factors.

As Dr Rahul Gupta, Senior Director and HOD, Neurosurgery, Fortis Hospital, Noida, explains, "The experience of pain is not identical for everyone."

Pain starts with an injury, but doesn't end there

Pain often begins when specialised sensory nerve endings, called nociceptors, detect potentially damaging stimuli such as heat, pressure or tissue injury. Signals travel through nerves and the spinal cord before being processed by the brain.

But nociception and pain are not the same thing. The IASP specifically notes that pain cannot be inferred solely from activity in sensory neurons. This helps explain why people with seemingly similar injuries can report very different experiences.

Pain can broadly involve different mechanisms. Nociceptive pain results from tissue damage or inflammation; neuropathic pain is associated with damage to the nervous system; and nociplastic pain involves altered pain processing without a clear ongoing tissue injury or nerve damage. 

Why can two people feel the same injury differently?

Several factors can influence how strongly pain is perceived.

1. Your nervous system and genes

Pain processing involves numerous chemical messengers, receptors and pathways in the nervous system. Genetic differences can influence how these systems respond. Dr Gupta says, "Differences in these chemicals, hormones and the sensitivity of nerve endings can alter how strongly pain is perceived. Genetic factors can also contribute to these differences."

Research reviewed by the National Institutes of Health also identifies genetics, brain function, the nervous, immune and endocrine systems as biological contributors to individual pain experiences.

2. Age and existing health conditions

Age and underlying health can change both pain perception and recovery. Someone with diabetes, osteoporosis, rheumatoid arthritis or other chronic conditions may respond differently to an injury than an otherwise healthy person.

Diabetes is particularly important because prolonged high blood sugar can damage peripheral nerves. Depending on the type and extent of nerve damage, a person may develop pain, tingling or, in some cases, reduced ability to feel touch, temperature or pain.

That reduced sensation can create another problem: an injury may not hurt enough to immediately alert someone that something is wrong. Dr Gupta points out that nerve involvement in conditions such as diabetes and leprosy can reduce pain sensation, potentially allowing injuries or other problems to go unnoticed for longer.

A less painful injury isn't necessarily a minor injury

This is an important distinction. Pain intensity does not always correspond directly to the extent of physical damage.

An injury can cause substantial damage while producing surprisingly little pain, particularly when sensation is impaired. Conversely, significant pain can occur even when the visible injury appears relatively small.

Two injuries that look similar externally may also have very different internal consequences. "There can be damage at a microscopic level that is not immediately visible on routine investigations," says Dr Gupta.

Damage to blood vessels, reduced oxygen supply, internal bleeding or significant blood loss can all influence the eventual outcome. This is particularly relevant with head injuries, where what happens inside the skull may not be obvious from the outside.

With brain injuries, timing can change outcomes

A head injury should never be judged solely by how much it hurts. Traumatic brain injuries can involve bleeding, swelling, bruising or other changes that affect brain function. Some symptoms may also appear or become more apparent later. (CDC)

Prompt medical assessment is therefore important, particularly when there are warning signs or a significant mechanism of injury.

Treatment decisions depend on the nature and severity of the injury. In certain traumatic brain injuries involving bleeding or pressure on the brain, guidelines recommend urgent surgical intervention when specific criteria are met. For example, the Brain Trauma Foundation recommends that acute subdural haematomas meeting surgical criteria be evacuated as soon as possible. 

Dr Gupta says, "In brain injuries, the time taken to receive medical attention is particularly important." He adds that prompt assessment, resuscitation and appropriate treatment can influence the extent of damage and eventual recovery.

Stress and fear can change the pain experience

Pain isn't just biological. Mood, fear, stress, expectations and previous experiences can influence how pain is perceived and how someone responds to it. The NIH describes pain as a biopsychosocial experience in which biological, psychological and social factors interact. Research also suggests that psychological distress, expectations, coping strategies and social circumstances can influence pain outcomes. 

This does not mean pain is "all in the head". Rather, the brain is an essential part of how pain is constructed and regulated. A person's psychological state can also affect whether they participate in physiotherapy, rehabilitation, medication schedules and follow-up care.

Recovery is more than healing the injury

The injury itself is only one part of recovery. Blood and oxygen supply, neurological damage, underlying medical conditions, treatment timing, rehabilitation, sleep, mental health and social support can all influence how someone progresses.

For people recovering from moderate or severe traumatic brain injury, rehabilitation may involve relearning physical or cognitive skills and addressing problems such as depression, sleep disturbances and persistent headaches.

Family and social support can also become particularly important during prolonged neurological recovery. Alcohol adds another complication after a head injury. It can alter behaviour and mental status, potentially making it harder to recognise or accurately assess neurological symptoms. A person who has sustained a head injury should therefore not assume that apparent intoxication explains away concerning changes in consciousness or behaviour.

When should pain after an injury be checked?

Persistent, worsening or unexplained pain should not simply be judged by its intensity. Medical assessment is particularly important when pain is accompanied by symptoms such as loss of consciousness, confusion, repeated vomiting, seizures, weakness, numbness, worsening headache, difficulty speaking, unusual behaviour or increasing drowsiness after a head injury.

Even after a seemingly mild concussion, symptoms that do not improve or become worse warrant medical review.

Pain is the body's warning system, but it is not a perfect damage meter. The brain, nerves, genes, age, underlying health, psychological state, treatment and rehabilitation can all influence what a person feels and how quickly they recover.

As Dr Gupta puts it, "Recovery is therefore not determined by the visible injury alone." That is why two people can walk away from seemingly similar injuries with very different experiences, and why severe pain should not automatically be equated with greater damage, while mild pain should never be assumed to mean that an injury is minor.

Read More: Why Women Ignore Pain Longer Than Men And How It Impacts Long-Term Health



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