Can a smile decrease the pain of an injection?

28 December, 2020
A recent review finds that both smiling and grimacing could decrease the sensation of soreness connected with a “vaccination-like needle injection.” A sincere smile also reduced stress-induced physiological responses in participants.

When humans face acute agony, they tend to close their eyes firmly, raise their cheeks, and bare their teeth. Selected animals use very similar facial expressions, which authorities often call the grimace response.

As the authors of the recent research make clear, “these facial musculature changes may also have a different interpretation: smiling.”

Why both of these expressions, which occur for completely different reasons, should share so various aspects is unclear. Experts from the University of California, Irvine Institution of Ecology recently attempt to “check whether these facial activities are beneficial in the context of pressure and pain.”

Specifically, they wished to understand whether manipulating participants’ facial expressions throughout a needle injection might impact their connection with pain and associated stress levels.

The researchers’ findings come in the journal Emotion.

For quite some time, scientists have already been interested to understand the impact of facial expressions on soreness perception and mood. The facial responses hypothesis, for instance, says that activating facial muscles can boost or reduce emotional experience. These results on emotion can occur even if experts manipulate a participant’s facial muscles into a manifestation.

As the authors of the recent study clarify, “feigning a smile, whether conscious or certainly not, may alter feelings in a great way.”

The study
To research possible links somewhere between facial expression and discomfort sensation, the researchers recruited 231 participants. The individuals all received a go of saline solution by using a needle very similar to those employed to deliver a flu vaccine.

The experts split the participants into four teams. Before and during the shot, the researchers manipulated participant’s faces in to the following different expressions employing chopsticks held in the oral cavity:

A good Duchenne smile: a sincere smile, where in fact the corners of the oral cavity come up and wrinkles appear around the eyes
  • a non-Duchenne smile
  • a grimace
  • a neutral expression
Example photographs of how the researchers applied the chopsticks to elicit these expressions are available here.

Prior to the injection, participants completed a questionnaire that asked how anxious these were about the needle.

As the individuals held their facial expressions, a physician administered the saline injection. After the practitioner had used a bandage, the participant taken out the chopsticks from their oral cavity and finished a questionnaire about how precisely much pain they were experiencing.

After 6 minutes of relax, the participants once again reported their pain amounts. The researchers also asked them how demanding the experience was.

Before, during, and following the injection, the individuals were associated with an electrocardiogram. On top of that, the researchers measured adjustments in the electric resistance of participants’ pores and skin, or electrodermal activity (EDA). EDA is a way of measuring emotional or physiological arousal.