Here’s Everything Researchers Know About High Sensitivity, as of 2021

ByProfessor Michael Pluess
A researcher presenting sensitivity research

One of the world’s top HSP researchers explains eye-opening breakthroughs in sensitivity research — and what they mean for HSPs.

Sensitivity as a personality trait is still considered a relatively new concept within the field of psychology, but it’s been actively researched by academics and practitioners for at least 25 years. That means now is a good time to take stock of what we know, what we don’t, and how sensitive people can most benefit from ongoing research. I don’t say that lightly: As one of the researchers directly involved in this work, I believe that the more we understand about sensitive people, the better we’ll be able to meet their needs. And I’d like to make our knowledge as accessible as possible. 

To do that, I’m going to put everything we know about sensitivity in easy-to-understand terms, starting from the early days and working all the way up to the present. Given the large number of studies undertaken over this time period (1), the current summary does not seek to cover all of the various contributions to the field, but rather highlights those that are most relevant for the purpose of general understanding — including some of the most eye-opening recent breakthroughs.

The Origins of Sensitivity Research

The earliest roots of sensitivity research actually stretch back 100 years when psychiatrist C.G. Jung proposed that some people are characterised by “an innate sensitiveness” (2). Since then, some parts of what we now call sensitivity have been investigated under different umbrellas (for example, while studying introversion, or in the context of behavior inhibition — our ability to control impulsive urges). It wasn’t until the mid-1990s when more specific theories on sensitivity emerged and researchers began to investigate sensitivity as a trait in its own right. These new theories sparked broad interest and stimulated new research. 

The First Theories of Sensitivity and Early Empirical Evidence (1995-2015)

Three Separate Theories

The first 20 years of sensitivity research largely focused a lot on theory. This is more important than it sounds — in psychology, it’s critical to have a solid theory in place before conducting empirical research to test and advance it. Three individual theories from different researchers emerged around the same time as a response to clinical observation or academic research on child development. The theories were:

  • Sensory Processing Sensitivity (SPS) by Elaine and Art Aron, who coined the term “highly sensitive person” 
  • Differential Susceptibility (DS) by Jay Belsky
  • Biological Sensitivity to Context (BSC) by Tom Boyce and Bruce Ellis

The common thread shared by these theories is that they all suggest that some people are especially strongly affected by what they experience. 

During the early days of sensitivity research, studies focused narrowly on some pretty specific details of how sensitivity worked, and each of these three theories took a different approach. For example, SPS research focused primarily on personality in adults, differential susceptibility focused on infants, and BSC focused on physiological stress reactions in children. 

One important early development was a self-report measure of sensitivity known as the Highly Sensitive Person Scale — basically, a series of questions people could answer that would profile how sensitive they are. This paved the way for a large number of follow-up studies that looked at how sensitivity was related to other traits (for example, it was during this period that we learned that sensitivity is not the same thing as introversion). 

Different studies also gathered different kinds of data: SPS research looked at adults, which helped us see what parts of human behavior are — and are not — related to sensitivity. Meanwhile, DS and BSC did so-called longitudinal research, following sensitive children over time from a young age. This gave key insights into what sensitive people need to thrive. 

Together, these kinds of studies provided strong empirical evidence for the concept of sensitivity as part of the human personality. This opened the door for the next step: exploring the brain function and genetics of sensitivity.

A Surge of New Breakthroughs (2015-2021)

The last five years of sensitivity research have been shaped by two major shifts:

  • The theory of environmental sensitivity. The way we view sensitivity has been refined, and the three early theories mentioned above have been combined into a single framework. We call this framework environmental sensitivity (3,4). Terms like highly sensitive person (HSP) — or “orchids and dandelions” — are simply different ways of describing this framework. 
  • More empirical research on sensitivity than ever before. Research broadened and sought a deeper understanding of the psychological, physiological, and genetic components of sensitivity. New ways of measuring sensitivity in children and adolescents were developed, including assessments based on behavioral observation by trained experts. 

These two shifts allowed a slew of breakthroughs in the past six years:

Breakthrough #1: It Turns Out, Sensitivity Is a Continuum

Up to this period, several theories tended to differentiate between two groups of people: those who are highly sensitive and those who are not. However, new studies in much larger samples during this period led to the discovery that sensitivity should be considered along a continuum (everyone is sensitive to an extent, and some are more sensitive than others). 

Using this continuum, people can be categorized into three sensitivity groups: low, medium, or high. Each of these three groups has their own strengths and weaknesses. You can think of these groups as dandelions, tulips, and orchids. Dandelions (low sensitive people) will grow anywhere, and survive harsh conditions. Orchids (highly sensitive people) require very specific growing conditions to flourish, but when they get their needs met, they’re positively stunning. Tulips (those in the middle) share a little bit of both groups. 

Highly sensitive people are now understood to make up about 30 percent of the population. (Earlier research suggested roughly 20 percent, but most studies — using both personality assessments and genetic tests — find the number is higher.)

Breakthrough #2: Sensitivity Has Its Own Personality Profile

During this period, significant progress was also made regarding the relationship between sensitivity and other common personality traits, pointing to a specific personality profile underlying sensitivity. Specifically, research found that sensitivity is characterised by heightened neuroticism and openness to experiences, with introversion playing a smaller role than previously assumed. In case that sounds like psychometrics jargon, I’ll translate: If you’re creative and open to new ideas, but your emotions often change without warning, there’s a good chance you would test as high in sensitivity. 

Breakthrough #3: A Sensitive Brain Comes from (Many) Genes

In relation to the neuroscience of sensitivity, the structure and function of several brain regions, such as the hippocampus and amygdala, were found to play an important role. Meanwhile, access to new measures and larger samples also allowed for substantial advancements in our understanding of the role of genetics in sensitivity, with studies finding that about 50 percent of the differences between individuals can be explained by genetic factors — in other words, to a large degree, if you are sensitive, you were born that way. Furthermore, these genetic factors are distributed widely across the whole genome rather than reflecting a single “sensitivity gene.” 

Empirical research continued to build and expand into geographic locations, cultures, and contexts beyond the USA and UK, such as Italy, Belgium, Germany, Lebanon, Japan, and South Africa, to mention just a few examples. Finally, and importantly, research designs were also strengthened over this time, with studies adopting more experimental and longitudinal approaches. They also increasingly investigated sensitivity in response to positive experiences rather than focusing on predominately negative ones, highlighting the many benefits of high sensitivity. 

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What We Don’t Know — And Where the Research Is Going Next (2021-2030)

Although there has been significant progress in research on sensitivity over the last 20+ years, our current knowledge has gaps that need to be addressed in future research.

Among these is the question of how exactly sensitivity develops over time and whether it is set in childhood or can develop further in adulthood. In order to investigate this, we need to continue improving our ability to accurately measure sensitivity by identifying and capturing the most essential features of sensitivity. Ideally, such measures will be objective, applicable to people across different ages and cultures, and include biological components of sensitivity, as well. 

Likewise, while there has been some initial progress in our understanding of the biology underlying sensitivity, much more work is needed with a focus on neuroscience, physiology, and genetics. Carefully planned neuroscientific and physiological studies are fundamental in order to advance our understanding of sensitivity. However, genetic studies may be more challenging to undertake, given that they require very large sample sizes (north of 100,000 people). 

Finally, an improved measurement of sensitivity is also vital to advance our understanding of the relationship between sensitivity and mental health. 

Every Breakthrough Helps Improve HSP Lives

The seeds of early research on sensitivity, sown 25 years ago, have sprouted and grown into a solid tree. With an increasing number of colleagues across the globe joining research efforts, this tree is likely to grow substantially over the next 10 years. At the same time, sensitivity has also been gaining more attention in the public eye, as evidenced by the increasing number of books, blogs, and media coverage on the topic. In short, these are exciting times for research on sensitivity! 

While we have come a long way already, the journey continues and is likely full of exciting discoveries — each of which can help improve the lives of sensitive people and change the way society sees them for the better. 

For information and updates on the latest research, as well as access to online sensitivity self-tests, visit our website SensitivityResearch.com, which is run by a group of researchers dedicated to sharing reliable knowledge on the human trait of sensitivity.

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References:

1. Greven, C. U., Lionetti, F., Booth, C., Aron, E. N., Fox, E., Schendan, H. E., . . . Homberg, J. (2019). Sensory Processing Sensitivity in the context of Environmental Sensitivity: A critical review and development of research agenda. Neuroscience and Biobehavioral Reviews, 98, 287-305. doi:10.1016/j.neubiorev.2019.01.009

2. Jung, C. G. (1913). The theory of psychoanalysis. Psychoanalytic Review, 1(1), 1-40.

3. Pluess, M. (2015). Individual Differences in Environmental Sensitivity. Child Development Perspectives, 9(3), 138-143. doi:10.1111/cdep.12120

4. Pluess, M., Lionetti, F., Aron, E., & Aron, A. (2020). People Differ in their Sensitivity to the Environment: An Integrated Theory and Empirical Evidence. PsyArXiv

Michael Pluess is a Professor of Development Psychology at Queen Mary University of London and a leading expert on sensitivity in children and adults. He has made significant theoretical and empirical contributions in the field, along with the development and validation of sensitivity measures. He leads several large research projects on sensitivity across the world, and is part of the senior leadership team at SensitivityResearch.com.