Thousands of years after acupuncture was invented, controversy remains over whether the Chinese traditional medicine technique works. While previous trials have shown mixed results, a new study shows that, at the very least, those needles really do cause something to happen in our bodies.

Scientists have long been skeptical about the value of acupuncture, though practitioners have questioned whether the acupuncture in many studies was done “correctly.” Other trials suggest that acupuncture does “work,” but only as a placebo. In a study published this week in the journal Evidence-based Complementary and Alternative Medicine, researchers measured the biological effect of the procedure. They found that if you do acupuncture correctly, your body releases more nitric oxide at the points where the needles are inserted. The nitric oxide increases blood flow and triggers your body to release natural anesthetics, which can create either warming or cooling sensations. (The study was funded in part by the National Institutes of Health.)

The scientists inserted acupuncture needles into 25 people, ages 18 to 60 and both men and women. Then they tried two different methods. In one, they twisted the needles for two minutes every five minutes, for a total of 20 minutes. In the other, they applied electrical heat for 20 minutes.

Using a device that can measure the molecules in specific skin regions, researchers were able to detect the nitric oxide being released at these acupuncture sites for both methods.

There are caveats, as always. The sample size is small, and these results should be considered in light of more skeptical research as well. Next, the team wants to do further research to understand the underlying cellular mechanisms and the differences between the two techniques.