The purpose of pain is to protect the body by warning it of both internal and external damage. Pain is sensed by free nerve endings found in the skin, the membranes that surround the internal organs, the bladder and the muscles. There are no pain receptors in the brain or liver, but the membranes that cover them warn of sources of pain coming from outside.

Tight clothing can squeeze in the morning, but after a few hours the tightness is no longer noticeable. Pain, however, does not work the same way as other sensations do. Even if you do not get used to a particular kind of pain, you can learn to control the sensations caused by it. For example, if you think about pleasant things or keep yourself busy, the pain sensation is not as dominant in the brain as it is if you actively think about pain.

Often, pain is not felt at its actual source. For example, a headache is usually caused by tension in the muscles of the shoulders. When no blood circulates to the shoulder muscles, the resulting loss of oxygen causes pain that is sensed as a headache. Similarly, heart pain can be felt in your hand. Likewise, when you hit your elbow the nerve pain can be felt in your little finger. This happens because information from several areas of the body often travels through the same nerve pathways in the spinal cord and the brain.

Painkillers prevent nerve impulses caused by pain from reaching the brain, so that the pain message is not transmitted. Excessive intake of painkillers will reduce their effectiveness and may even cause poisoning. The cause of the pain should be treated first, whereas the pain itself should only be taken care of after its cause has been determined.