Acupuncture is a method of encouraging the body to promote natural healing and to improve functioning. The classical Chinese explanation is that channels of energy run in regular patterns through the body and over its surface. These energy channels, called meridians, are like rivers flowing through the body to irrigate and nourish the tissues. An obstruction in the movement of these energy rivers is like a dam that backs up in others.
The meridians can be influenced by needling the acupuncture points; the acupuncture needles unblock the obstructions at the dams and re-establish the regular flow through the meridians. Acupuncture treatments can therefore help the body's internal organs to correct imbalances in their digestion, absorption, and energy production activities, and in the circulation of their energy through the meridians.
The modern scientific explanation is that needling the acupuncture points stimulates the nervous system to release chemicals in the muscles, spinal cord, and brain. These chemicals will either change the experience of pain, or they will trigger the release of other chemicals and hormones which influence the body's own internal regulating system.