Babies’ facial expressions after jab reveal pain type

By Piriya Mahendra, medwireNews Reporter

Researchers have discerned seven distinct facial expressions in babies immediately after vaccination, which they say could signal different types of pain and aid communication of distress to caregivers.

Rebecca Riddell (York University, Toronto, Canada) and colleagues say that their findings show that a single stereotyped pain expression during infancy does not exist.

"By tracking the occurrence of infants' facial expressions over the first minute post needle and the decrease of acute pain responding in infancy over the first year of life, we can attempt to speculate about the communicative goals of the facial expressions discerned and how they may change as the infant ages," they explain.

As reported in Pain, Riddell and team categorized babies' facial expressions using the Facial Action Coding System for Infants and Young Children (BabyFACS). According to this system, the authors found that the expression of the Red facial type (defined as cry, accompanied by oblique eyebrows) within 1 minute of a vaccination varied significantly according to age. For example, 7.49% of 2-month-old babies showed the Red facial expression compared with 5.12% of 4-month olds, 9.51% of 6-month olds, and 18.87% of 12-month olds.

Expression of the Orange facial type (cry from horizontally stretched mouth, open eyes) did not change significantly with age, however, while the Yellow facial type (big cry from horizontally or vertically stretched mouth, open eyes) was expressed at a "generally stable" frequency across ages.

The Green facial type (horizontal mouth, closed eyes) changed significantly with age, with 2.49% of 2-month olds expressing it compared with 2.40% of 4-month olds, 2.51% of 6-month olds, and 0.00% of 12-month olds.

The Blue facial type (big cry from horizontal or vertical stretched mouth, closed eyes) was also differentially expressed across age, at 25.70% in 2-month olds, 13.50% in 4-month olds, 9.85% in 6-month olds, and 3.56% in 12-month olds.

There was no age difference in the average occurrence of Purple facial expressions (any cry without raised cheeks or eyelid tightening), but there was in Black facial expressions (no cry, no mouth stretching), which occurred in 4.26% of 2-month olds, 3.20% of 4-month olds, 3.60% of 6-month olds, and 11.24% of 12-month olds.

The authors say that each facial expression is attached to a different type of distress. For example, they suggest that the Blue expression demonstrates complete sensory overwhelm, while the Yellow expression may reveal an attempt to regulate intense distress.

"We propose that these seven categories of expressions may have evolved to allow infants to communicate two crucial broad states to caregivers: level of distress and degree of regulation from distress," write Riddell et al.

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