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Medically reviewed by Last updated on Oct 25, 2023.

What is Pain?

Harvard Health Publishing

You accidentally touch a hot stove. In a millisecond, you jerk your hand away. What just happened?

You have pain receptors throughout your body, both outside and within. These receptors send electrical messages through your spinal cord to the brain. You only become aware of pain after your brain receives and interprets these electrical messages. In some cases, such as when you touch a hot stove, the body can spring into defensive action even before the brain knows what is happening. That's because pain messages that reach the spinal cord can cause an automatic reflex response, making muscles near the source of the pain contract to get away from the pain.

Pain receptors and nerve pathways differ throughout the body. Therefore, the sensation of pain differs, too, depending on where the message comes from and how it travels. At times, the source of pain is difficult to locate. For example, some people feel the pain from a heart attack in the neck or jaw. People also differ in their ability to tolerate pain and how they respond to pain medication.

Pain is classified into two types:

Acute pain:

  • Usually has a clear source
  • Begins suddenly
  • Doesn't last a long time
  • Can increase heart and breathing rates and raise blood pressure

Acute pain is generally useful. It's a clear sign of danger. Examples include touching a hot surface, stubbing your toe or being cut.

Chronic pain:

  • Usually lasts a month or more, and could last years
  • Can come and go many times or remain constant
  • Can disturb sleep patterns, decrease appetite and cause depression
  • Often has little or no effect on blood pressure, heart or breathing rates

Chronic pain can outlive its usefulness; the message has been sent and received, but keeps being sent over and over. Examples include arthritis, cancer and back injuries.


Pain is the symptom. Acute pain often has a clear source and may be described as  sharp, radiating, stabbing or boring. Chronic pain is more persistent, lasting months or years, and it may or may not have an obvious source and more often described as throbbing or aching. In some cases, it is accompanied by numbness or tingling.


To diagnose the cause of pain, doctors usually try to determine the intensity of the pain and what's causing the pain. This can be challenging. No laboratory test can prove that pain exists, and describing pain in words can be difficult. Also, each person experiences pain differently.

Your doctor may ask you questions about the history of your pain. He or she may ask you to describe your pain using a scale, such as 0 (no pain) to 10 (unbearable pain), or use other scales and measurements. Once your doctor determines whether your pain is acute or chronic, and uncovers the source of the pain, he or she can determine the best way to treat it. However, doctors often begin treating pain before they identify the cause.

Expected Duration

How long pain lasts will depend on its source and severity.


Trying to prevent pain before it happens can be dangerous. Acute pain is an important message that is essential to survival. Some people are born with a rare disorder (congenital analgesia) and do not feel pain. They live in great danger because they miss warning signals that could mean life or death.

Once the cause of pain is diagnosed, it may be possible to prevent the pain from coming back. For instance, a person diagnosed with a stomach ulcer can take medications to heal the ulcer and prevent continuation of the pain.


Your doctor probably will treat your pain while he or she tries to figure out the cause. Many drugs are helpful, though how well they work depends on the patient and the nature of pain.

Analgesics (painkillers) are the most common pain remedy. Acetaminophen (Tylenol and other brand names) interferes with pain messages. Aspirin and ibuprofen (Advil, Motrin and others) work in two ways: 1) by interfering with pain messages, and 2) by reducing inflammation, swelling and irritation that can make pain worse.  Topical pain relievers (such as lidocaine patches, IcyHot, Aspercreme or BenGay) may lessen pain by numbing the area, reducing inflammation or  causing a form of skin irritation that "distracts" the brain from focusing on pain.

Narcotic pain relievers, such as morphine and codeine, are the most powerful pain treatments. These usually are reserved for the most intense pain. They can cause serious side effects, can be addictive and often cause constipation.

Other drugs such as anesthetics, antidepressants, anticonvulsants and corticosteroids may work against certain types of pain.

Sometimes medications are injected directly into the region of pain or near a nerve to interrupt the pain signal.

Non-drug treatments for pain include:

  • Acupuncture
  • Massage
  • Relaxation
  • Psychotherapy
  • Transcutaneous electrical nerve stimulation (TENS), which uses electrical impulses to stimulate the nerve endings at or near the site of pain

Non-drug treatments may be especially useful for people with chronic pain. In some cases, these treatments may stimulate natural painkillers, called endorphins, which are created within the body. In other cases, non-drug treatments work directly on nerves to interfere with pain messages. Sometimes, it isn't clear why the pain stops.

Treatment options

The following list of medications are in some way related to or used in the treatment of this condition.

View more treatment options

When To Call a Professional

Pain means some kind of problem exists. And while different people tolerate different degrees of pain, you should never ignore pain. Consult a doctor if you cannot determine why you are experiencing pain, if pain continues or if it doesn't respond to simple treatment.


For people with acute pain, the outlook is usually good. Many drugs are effective in relieving pain. When the cause of the pain is removed, the pain subsides.

People with chronic pain may have a more difficult time. The sources of pain can be hard to find and difficult to treat, and pain may continue even after its causes are addressed. Chronic pain can cause complications such as sleep disorders, loss of appetite and depression. Doctors are learning more about the causes and treatment of chronic pain, but chronic pain sufferers may need to learn to cope with pain for a long time. Lifestyle changes and non-drug treatments may need to become a part of daily life.

Additional Info

American Pain Society


Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.