Either a sincere smile or grimace can reduce the pain of a needle injection by as much as 40%, according to a new study.

A genuine, or Duchenne, smile—one that elevates the corners of the mouth and creates crow’s feet around the eyes—can also significantly blunt the stressful, needle-related physiological response by lowering the heart rate.

“When facing distress or pleasure, humans make remarkably similar facial expressions that involve activation of the eye muscles, lifting of the cheeks, and baring of the teeth,” says principal investigator Sarah Pressman, professor of psychological science at the University of California, Irvine.

“We found that these movements, as opposed to a neutral expression, are beneficial in reducing discomfort and stress .”

The study involved 231 people who self-reported levels of pain , emotion, and distress in response to a 25-gauge-needle—the same as used in a typical flu shot—injection of saline solution. Participants were randomized to express either a Duchenne or non-Duchenne smile, a grimace, or a neutral expression—each facilitated by chopsticks held in the teeth.

Those in the Duchenne smile and grimace groups reported that the injection hurt only about half as much as those in the neutral group, indicating that these actions can make a positive difference in the needle jab experience. The more sincere Duchenne smile was also associated with significantly lower heart rates.

“Our study demonstrates a simple, free, and clinically meaningful method of making the needle injection less awful,” Pressman says.

“Given the numerous anxiety- and pain-provoking situations found in medical practice, we hope that an understanding of how and when smiling and grimacing helps will foster effective pain reduction strategies that result in better patient experiences.”

The research appears in the journal Emotion . Additional coauthors are from UC Irvine; the National Cancer Institute; the University of Oregon; and CHI St. Alexius Health, in Bismarck, North Dakota.

Source: UC Irvine

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