Smiling Faces

A new and highly novel investigation on the impact of nonverbal feedback in the form of a subset of “smiles” from another can either reduce or increase physiological stress as measured by salivary cortisol levels.

Investigators Martin, Abercrombie, et al (2018) from the University of Wisconsin and Bar-Ilan University demonstrated that one’s perception and interpretation of the meaning of another’s smile has a significant impact on Hypothalamic-Adrenal Axis (HPA) activity, especially when perceived as “evaluative” during stressful social circumstances.

The HPA axis, which has traditionally been seen as the body’s “stress system”, which through complex endocrine and neurobiological system, mediate cortisol and other important stress related hormones. However, the recent research is beginning to illuminate other important functions of the HPA axis, including the regulation of our energy levels, via its action on specific hormones, neurotransmitters, which appear to play an important role in energy expenditure and both the immune and digestive systems.

This makes sense when you consider the role of the hypothalamus as a mediator between the CNS and endocrine system. A primary example is the regulation of hunger and satiety via release and inhibition of leptin and ghrelin in the paraventricular nucleus of the hypothalamus.

Moreover, the interface of the pituitary gland, the hypothalamus, controls the function of “peripheral” endocrine glands which determine the volume of adrenalin and circulating thyroid levels.

The study by Martin and colleagues demonstrated the effect that emotional perceptions of both verbal and nonverbal social cues on HPA induced physiological response by measuring salivary cortisol levels in 90 subjects. Cortisol prevalence is a reliable indicator of emotional and physiological levels of stress.

Using a subset of distinct smiles as the controlled variable, the researchers discovered that certain types of facial expression conveyed dominance and were perceived as challenging the subject’s social standing, and was thus interpreted as disapproval. In this scenario, increased salivary cortisol resulted on increased heart rate. Additionally, these subjects took longer to return to their normal metabolic state after stimulus was introduced. The physiological response to ‘feeling evaluated’ or ‘judged’ as a result of nonverbal cues was concordant with the influence of negative verbal feedback.

By contrast, smiles interpreted as showing ‘affiliation’ or reward were more likely to facilitate low stress levels and increase the likelihood of social bonding similar to the effect of overt friendliness and positive verbal social evaluation. In this scenario, a smile perceived friendly and accepting thwarted the stress response, confirmed by decreased cortisol production.

Why Does This Matter?

These data suggest that facial expressions have deep physiological and emotional implications and that smiles regulate the social world in a highly nuanced fashion.

It may sound like a stretch, but as my good friend and colleague, Dr. Robert DuPont, said in the late 1980s, drugs of abuse could override the instinctual survival drives in rodents. What is less known regarding this famous experiment is that highly socialized and pair bonded rats were least likely to become addicted, harmed or killed when allowed to freely administer either a cocaine or opioid solution. Social bonding and acceptance are even more powerful among humans.

In the treatment setting for substance use disorders, patients whose family fully participates in the family program, with the goal of healing their relationship, help engagement, adherence, and these patients are least likely to relapse.

Humans are highly social creatures who require a certain level of social attachment and bonding to thrive as infants. This desire for acceptance and unconditional love is communicated largely by nonverbal communication, as is disapproval and rejection. We are often unaware of our susceptibility and emotional reaction to these social cues. As we often tell our patients in the treatment setting, “When you are feeling lonely, discouraged or bad about yourself, a friendly smile or word of encouragement can be the difference between a bad day and a wonderful day. So instead of waiting for someone to smile or encourage you, take the initiative, even though you are having a tough time, and muster up a friendly smile and encourage someone else”. Patients are always amazed by the healing that will result for both parties.

Ask The Expert



Martin JD1Abercrombie HC2Gilboa-Schechtman E3Niedenthal PM4.Functionally distinct smiles elicit different physiological responses in an evaluative context. Sci Rep. 2018 Mar 1;8(1):3558. doi: 10.1038/s41598-018-21536-1.