The Developmental Origins of High Sensitivity

Study background

Many personality traits, health characteristics, and disease states emerging in adults can be traced back to events and experiences that occurred during their early years in childhood. For example, infants with low birth weight have a higher chance of developing obesity and type 2 diabetes as adults compared to normal birth weight infants (1).

Similarly, pre-term babies are more likely to develop shy, cautious temperaments (2). These sorts of discoveries underscore why childhood is a key focus of both psychological and medical research (3).

What about sensitivity? Can we trace the origins of adult sensitivity back to childhood? In 2011, researchers Michael Pluess and Jay Belsky (4) theorised that individual levels of sensitivity begin to form as early as during pregnancy in the mother’s womb.

In support of this claim, they found that low birth weight tended to be more common amongst children with difficult temperaments (who typically develop into adults with higher sensitivity).

Although a promising start, no other attempts have since been made to directly measure sensitivity in adults, and then investigate how levels of sensitivity correspond to childhood characteristics.

Aim of our study

Using South Africa’s largest longitudinal birth cohort (a group of research participants who are intermittently tracked from birth), known now as the Birth to Thirty cohort (https://bt30.org/), we aimed to identify what highly sensitive adults tended to share in common as young children, compared to less sensitive adults (5).

How was the study conducted?

During the years that cohort members turned 28-29 years old (2018-2019), we invited them to complete the Highly Sensitive Person scale (https://sensitivityresearch.com/self-tests/adult-self-test).

Where available, we then obtained historical records of members’ birth weight, gestational age, socioeconomic status, maternal education level, maternal prenatal stress levels, and caregiver ratings of internalising and externalising behaviour at age 7.

As adolescents, cohort members had donated a sample of their blood for genetic research. So we also decided to examine genetic variation at regions of the genome previously linked to sensitivity (namely the serotonin transporter linked polymorphic region and dopamine receptor D4).

Statistical modelling techniques were then used to confirm whether highly sensitive adults shared any childhood or genetic features compared to less sensitive adults.

Key findings

We found that highly sensitive adults were statistically more likely to have had a shorter gestational period. In other words, those cohort members whose gestational period lasted less than average (which, in our sample, was 38 weeks), had a higher probability of being highly sensitive as adults.

For those cohort members whose mothers answered surveys on prenatal stress levels, we found that higher maternal prenatal stress (instead of short gestational age) corresponded with higher sensitivity as an adult (Figure 1).

Importantly, short gestational age and maternal prenatal stress are known to be linked (6). Stressful pregnancies commonly result in shorter gestation periods, so it seems reasonable that we found a similar result for both variables in our study.

None of the other childhood variables we investigated appeared to correlate with adult sensitivity. We also couldn’t find any genetic differences between highly and less sensitive adults, although we only considered few such differences.

We know that temperament traits like sensitivity are influenced by the actions of hundreds of genes in our genome, so the potential genetic underpinnings of sensitivity await extensive future research.

Implications

Why is sensitivity more likely to be high in individuals born following short and/or stressful pregnancies? Is there a cause, or is this just a coincidental correlation? Unfortunately, we can’t answer those questions yet. However, the findings of our study do align with existing theory (4).

Currently, theory suggests that sensitivity is heightened in two specific contexts: either when pregnancy and childhood are stressful (as our study points to), or in cases when pregnancy and childhood are consistently stress-free and supportive (a rarer scenario, given the many pressures of the modern world).

In both scenarios, it benefits children to be highly sensitive, whether it’s to help them remain hypervigilant and hyperaware in stressful situations, or to help them soak in the benefits of a peaceful, nurturing childhood.

Although much more research is needed, our study provides an additional clue to the developmental origins of high sensitivity, and further encourages proper care and support for children, especially those born in stressful circumstances.