How does acupuncture relieve pain?

Traditional Chinese acupuncture involves the insertion of extremely fine needles into the skin at specific "acupoints." This may relieve pain by releasing endorphins, the body's natural pain-killing chemicals, and by affecting the part of the brain that governs serotonin, a brain chemical involved with mood. ref: https://www.health.harvard.edu/healthbeat/relieving-pain-with-acupuncture#