Acupuncture needles are sterile, disposable, and as thin as a hair. They bend easily, and could easily slip into the channel of a hypodermic needle. This is why there is very little if any pain during a treatment. Instead, most patients find these treatment extremely relaxing to the point of failing asleep.
The stimulation of an acupoint is triggered when a disposable, sterile needle is inserted. Information is then transmitted to the brain where it prompts the body to release hormones and chemicals that reduce pain, regulate the endocrine system, and calm the nervous system.
Endorphins (neuro-chemicals) relieve pain by increasing the flow of blood and oxygen to the affected areas.
Auriculotherapy is based on the theory that specific areas of the external ear correspond to specific areas of the body. The needles send a message to the brain activating those areas.