There are lots of theories - the primary being that reflexology works through the nervous system.
There are a large number of nerve endings in the feet, hands and ears which are where the 3 reflexology maps of the body are located.
When health imbalances occur, such as a stiff neck, blockages of various chemicals accumulate in the neck reflexes of the feet, hands and ears.
The longer there is neck tension, the thicker the blockage becomes. Because nerve impulses flow from the end of one nerve to the beginning of the next, blockage between nerves will reduce the amount of nerve energy going through the body. Without enough nerve energy supply in the body, its parts and functions, cannot perform in a healthy manner.
This concept is illustrated by corrosion that accumulates on the terminal of a car battery. The thicker the corrosion, less electrical current flows from the battery to the car. The car runs rough. For the car to run smoothly, the corrosion must be cleaned off the battery terminal, so that the electrical current can flow fully.
So you see, for the neck to feel better, blockage between nerve endings in the neck reflexes of the feet, hands and ears must be eliminated, so that the current through the nerves can flow fully to the body again. When full nerve flow is restored, the body can balance itself and is better able to heal itself.
Reflexology works for many reasons. Besides normalizing nerve supply, beneficial chemicals are released during reflexology.
One most commonly known group of chemicals is endorphins - the body's natural opiates. Endorphins induce a sense of well being and are natural pain reducers.
Stress causes organs and glands to become either overactive of interactive. Reflexology helps to normalize the body's functions, stabilizing under or over active activity.
So some of the reasons people get better by having reflexology sessions are that the nerve energy supply is improved, there is an increase of beneficial chemicals and the body is normalized.