Grin and Bear It: Why Smiling Makes Vaccine Shots Less Painful

By Pat Anson, PNN Editor

Over the next few months, tens of millions of people around the world will be getting the first injections of COVID-19 vaccines, with some getting a vaccine that requires two shots to be effective.

Whether it’s a shot for the flu, pneumonia, shingles or COVID, no one looks forward to stabbing pain from the oversized needles often used in vaccinations. Is there anything you can do to help relieve the sting from a needle prick?

An unusual study led by researchers at the University of California, Irvine, found an unexpected way to dull the pain: Put a big smile on your face.

Researchers say that a broad smile -- one that elevates the corners of the mouth and creates crow's feet around the eyes -- can reduce the pain of a needle injection by as much as 40 percent. That genuine smile, known as a Duchenne smile, can also lower your stress and heart rate during a needle injection.

If you find the idea of smiling during an injection a little silly, then feel free to grimace instead. Grimacing uses the same facial muscles as smiling and is just as effective at pain relief, according to researchers.

"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 lead investigator Sarah Pressman, PhD, a professor of psychological science at UCI. "We found that these movements, as opposed to a neutral expression, are beneficial in reducing discomfort and stress."

To test their theory, Pressman and her colleagues found 231 healthy volunteers who self-reported their levels of pain, emotion and distress while being injected in the upper arm with saline from a 25-gauge needle — the type often used in a flu shot.

Before and during the injection, participants were randomly selected to use either a Duchenne smile, a small smile, a grimace or a neutral expression. All four facial expressions were facilitated by holding chopsticks in their teeth.

Those in the Duchenne smile and grimace groups reported 40% and 39% less pain, respectively, during the injection than the neutral group, while participants in the small smile group had 26% less pain.

The Duchenne smile and grimace groups (images C and D) were also associated with slightly lower stress and heart rates.

“Why did these two disparate expressions perform so similarly? As discussed previously, this overlap could be explained by the fact that similar muscle groups are activated in both expressions,” researchers reported in the journal Emotion.

“Grimacing has long been used as a nonverbal indicator of pain and has been manipulated unintentionally via common medical practices from the Middle Ages that tell individuals to ‘bite down’ on pieces of wood and leather during painful procedures. To our knowledge, this is the first experimental test showing that this natural response to pain is helpful in improving the subjective pain experience.”

The researchers aren’t suggesting a return to the Middle Ages or that you bite down on chopsticks the next time you’re vaccinated. But they do think that “device-in-mouth manipulation” and “creative paradigms to manipulate facial expressions” are worthy of future pain research.     

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