Elaine Aron’s SPS is just one of four theories that researchers are pursuing — and all four may be pieces of the same puzzle. What can HSPs learn from them?
If you’re a highly sensitive person (HSP), you’ve probably heard it so often you know it by heart: the scientific term for the trait of sensitivity is Sensory Processing Sensitivity.
But what if it it’s not?
Elaine Aron, the psychologist behind the theory of Sensory Processing Sensitivity (SPS), is a legend (and, in my opinion, the “godmother” of HSPs). And SPS itself is still a current and accepted theory. Yet Aron is just one one of dozens — possibly even hundreds — of sensitivity researchers, and her theory is not the only one.
Yet it’s the only one most people have heard of.
That’s a real loss for HSPs, because other sensitivity researchers have developed models that explain key parts of what it means to be sensitive and how we can thrive. And their theories have been advanced not only with Aron’s encouragement, but often with her active participation. In this article, I’d like to introduce you to the four main theories scientists have for sensitivity and HSPs — and the new kid in town that may unite them all.
Are Other Scientists Stepping on Elaine Aron’s Turf?
I want to get this out of the way first: none of these researchers are stealing Aron’s work, and none of them are trying to crowd her out of the limelight. (In fact, when Aron got questions about this from her audience, she actually invited one of the other researchers to do a guest post on her blog to show that she supports his work.)
There are at least three reasons for this:
- Several of the other leading theories were being developed around the same time as Aron developed SPS — in the early to mid 1990s. All of these researchers, including Aron, were themselves building on the earlier work of scholars before them, like Jerome Kagan, who could be said to be the first true sensitivity researcher.
- This is how science works: different scholars develop different theories and interpretations of the same phenomenon, and over many decades they distill down into ever-sharper truths. Sensitivity research is a young field, and the contributions of all of the theories are crucial to better understanding HSPs.
- Finally, Aron herself has co-authored papers about some of the other theories, and regularly co-authors about sensitivity in general. The proponents of each theory all refer to each other’s work and build on it. (They also generally agree that they’re all talking about the same trait.)
The real reason we have different theories is because they emerged from different academic disciplines, and they each help explain a different part of sensitivity. For example, figuring out why nature evolved sensitivity in the first place tells us nothing about how a highly sensitive person’s brain is wired. And learning about brain wiring does not, in itself, give us actionable tools for HSPs to use in their everyday lives. For that reason, I suggest looking at the four theories not as rivals but as each being different pieces of the same puzzle.
So, without further ado, let’s look at the four main theories of sensitivity — and why we need each one of them.
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The 4 Scientific Theories Behind Highly Sensitive People
At present, the four dominant theories and models of sensitivity are:
- Sensory Processing Sensitivity: The theory that highly sensitivity people process information more deeply than others, and come with distinct traits because of it.
- Differential Susceptibility: The theory that natural selection favors a species that “hedges its bets” by having some offspring who are more affected by their environment (HSPs) and others who are less affected (non-HSPs).
- Biological Sensitivity to Context: The theory that children “become” more or less sensitive based on their early childhood experiences.
- Diathesis-Stress vs. Vantage Sensitivity: Two models of sensitivity that explore how and why sensitive people struggle more in adverse conditions (Diathesis-Stress) or benefit more from supportive conditions (Vantage Sensitivity).
Each one is a fascinating lens for understanding your sensitivity. Let’s look at each theory in detail:
1. Sensory-Processing Sensitivity (SPS)
Sensory Processing Sensitivity is the theory that highly sensitive process information more deeply. This deeper processing leads to a set of sensitive traits including empathy, sensitivity to subtle sensations, and overstimulation.
Sensory Processing Sensitivity is Elaine Aron’s theory which views sensitivity as primarily a temperament trait — just like you might be more of a numbers person or more of a visual person, you might be more sensitive or less sensitive. SPS proposes that highly sensitive people process information more deeply at a brain level. As a result, SPS suggests that sensitive people tend to be more emotionally reactive, have higher empathy, are more attuned to subtle physical sensations, and get overstimulated easily.
Some of the most important contributions of SPS include:
- Depth of Processing: SPS is the only theory that explicitly explains sensitivity as a cognitive difference (sensitive people process information differently at a brain level). This hypothetical “depth of processing” has been supported by some brain research but is not yet proven.
- The HSP Scale: Aron’s work on the SPS theory included developing a test anyone could take to assess their sensitivity, known as the HSP Scale. The HSP Scale has now been revised and thoroughly vetted for effectiveness and accuracy. It’s such a useful tool that even researchers who focus on the other theories often use the HSP Scale in their work.
- How Sensitivity Relates to Personality Traits: SPS research has gone a long way in helping prove that sensitivity is not the same thing as introversion, neuroticism, emotionality, or other personality traits.
Some reasons to be cautious about Sensory Processing Sensitivity include:
- It’s a “kitchen sink” explanation. One challenge of SPS is that it views high sensitivity as a single concept where the same person who is emotionally sensitive is also physically sensitive and also a deeper thinker. In reality, people may be more sensitive in one of these areas and less in the others. SPS has addressed this by developing “subscales” that you can think of as three “types” of highly sensitive people. The three types are not mutually exclusive, and you can qualify as one, two, or all three types.
- Depth of Processing doesn’t explain sensitivity on its own. It’s likely true that highly sensitive people process information more deeply, but this doesn’t explain why. The other theories use biological and child development research which might help answer that question. (Aron herself refers to Differential Susceptibility, one of the other theories, to help explain SPS.) There’s also a lot more to be done in terms of brain research to explain how this deeper processing happens.
- The numbers: Although Aron’s work continues to argue that 15-20 percent of people score high for SPS, most researchers find that the number is roughly 30 percent.
SPS is the most widely known name for sensitivity among the general public, due to Aron’s bestselling 1997 book The Highly Sensitive Person and her large online following. However, SPS is not necessarily the dominant theory among researchers. Instead, SPS is viewed as one of several leading, evidence-supported theories that likely all refer to the same trait.
2. Differential Susceptibility
Differential Susceptibility is the theory that evolution favors a species that “hedges its bets” by having some children who are more shaped by nurture (HSPs), and other children who remain fixed regardless of nurture (non-HSPs). Each one is better suited to a different kind of childhood environment.
Differential Susceptibility was first proposed by J. Belsky, a research psychologist focused on child development. Belsky could see that some children are strongly affected by “nurture” (their childhood environment), while other children are not — they stayed pretty much the same regardless of the kind of nurture they receive. You can think of the first group as highly sensitive children (and adults), and the second group as non-HSPs.
The question Belsky wanted to answer was: why?
Belsky looked to evolution and biology to find his answer, and developed the Differential Susceptibility theory. Differential Susceptibility proposes that natural selection has to develop children who can survive in a wide variety of environments. For example, some will be born into resource-rich environments with lots of support from family and lots of opportunities for growth. Others will be born into environments racked by scarcity, adversity, and a lack of care or nurture from family. Still others — probably most kids — will be born into a middle-of-the-road environment that doesn’t lean toward either extreme.
Since it’s pretty random which kind of environment a child gets, nature had to hedge its bets: it needed to develop more than one kind of child. HSPs and non-HSPs are the two models it came up with.
Under this theory, HSPs are the kids who are built for the extreme environments, because they are strongly affected by nurture. In the best environments, HSP children will soak up all of the love, support, and nurture, and use those resources to springboard ahead of others. Surprisingly, however, HSP kids are also the ones best suited to the worst environments. To be clear, because of their sensitivity, they will be utterly devastated and traumatized by a toxic upbringing — but they will survive it. They’ll survive because their sensitivity ensures they will learn the moods and cues of the abusive adults in their life. It ensures they will be properly vigilant for danger (as well as rare opportunities to snag a resource or a lucky break). And it ensures they will be cautious about taking risks that could make things even worse. Their sensitivity will keep them alive.
The second kind of child, the non-HSP, is built for the middle-of-the-road environment. They won’t be affected much by nurture, so it won’t bother them as much when there are good times and bad times, disappointments and successes, times of encouragement and times of distress. They’ll just go along to get along.
Because Differential Susceptibility uses evolution to explain differences in nurture and personality, it essentially argues that highly sensitive people are “born that way.”
Interestingly, although Differential Susceptibility is probably one of the least well-known of the sensitivity theories among the general public, it is probably the single best theory we have to explain why HSPs exist at all.
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3. Biological Sensitivity to Context
Biological Sensitivity to Context is the theory that certain types of childhood environments cause children to become more sensitive and reactive, while other childhood environments cause children to become less sensitive and reactive. Both strategies pay off in different ways and both lead to lifelong physiological differences.
Like Differential Susceptibility, Biological Sensitivity to Context also focuses on child development, but it takes almost the exact opposite approach. It was developed by W. Thomas Boyce, a pediatrician and psychiatrist, and Bruce J. Ellis, an evolutionary developmental psychologist, after they observed physiological differences between children — all of which had to do with the stress response. For example, some children had higher heart rates, stronger adrenaline response, higher cortisol levels and cortisol response, greater pupil dilation, and even brain differences in the adrenal cortex.
Ellis and Boyd wanted to know why some children would have such strong stress responses compared to others. What caused it?
Drawing on research about abuse and PTSD, among other factors, Ellis and Boyd proposed that a child’s early childhood environment actually causes a set of physiological changes that will stay with them long-term. Children in highly stressful and unhealthy environments, they suggested, will develop a higher stress response and essentially become more sensitive.
Interestingly, just like Belsky did, Ellis and Boyd found that children in the most supportive and nurturing environments also developed higher sensitivity, with roughly the same set of physiological differences. Again, the message was clear: the higher “alertness” of sensitive kids paid off in both the best homes, where it maximized the boost that the child got, and in the worst homes, where it allowed them to detect threats. (And, like Belsky, they found that middle-of-the-road environments favored lower sensitivity — the kids from those backgrounds developed a less active stress response system.)
So if the findings are so similar, what makes Biological Sensitivity to Context different from Differential Susceptibility?
It’s the explanation. Differential Susceptibility suggested that sensitive kids were born that way, and simply did better in certain environments. Biological Sensitivity to Context suggests that it’s the environment itself that makes kids more sensitive (or less sensitive). Or to put it another way: Differential Susceptibility focuses on nature, and Biological Sensitivity to Context focuses on nurture, although both theories do account for a mix of the two.
If you’re saying to yourself, “Well, it’s both,” you’re partly right (and all of the researchers involved would agree with you.) However, both theories are crucial because both help us understand a different part of what causes sensitivity.
(Also, if you keep stumbling over the name Biological Sensitivity to Context, it may help to know that this is the main theory behind the concept of orchids and dandelions — a much easier phrase to remember. Boyd is actually the author of the bestselling book by the same name.)
4. Diathesis-Stress vs. Vantage Sensitivity
The Diathesis-Stress model suggests that sensitive people struggle more with adverse or stressful conditions. The Vantage Sensitivity model suggests that sensitive people benefit more from positive and supportive conditions.
This is actually two separate models, but they are like two sides of the same coin.
Diathesis-Stress, a model borrowed from the study of mental health disorders, proposes that some individuals (HSPs) are hit harder by adverse circumstances and struggle more with stress; they are more “vulnerable.” If that makes you frown, that’s understandable, but bear in mind that the theory comes from a good place: sensitive kids are typically brought to psychologists when they’re struggling, not when they’re thriving, and researchers wanted to help understand and alleviate the stress these children were experiencing.
Vantage Sensitivity, a model developed by developmental psychologist Michael Pluess, proposes that HSPs benefit more from positive circumstance and get more out of resources and support; they get a bigger “boost.” (Vantage Sensitivity is the basis for the sensitive Boost Effect, arguably the single greatest gift that HSPs have.) Pluess actually developed Vantage Sensitivity specifically in response to the Diathesis-Stress view of sensitivity, and what he felt was an overall negative bias in the sensitivity literature in general. This is part of why Pluess is one of my personal heroes among the sensitivity research community!
Even Pluess, however, doesn’t think it’s all roses. He presents Vantage Sensitivity not as an argument against Diathesis-Stress, but as a companion to it. As Pluess said when I interviewed him, “Highly sensitive people struggle more in stressful environments, but benefit more from positive and supportive environments.” In other words, Diathesis-Stress and Vantage Sensitivity are a package deal.
These models are alone among the major theories in that they do not, in and of themselves, try to explain what causes sensitivity or even necessarily how it works. They rely on the other theories for that. Instead, Diathesis-Stress and Vantage Sensitivity seek to understand the challenges and advantages that sensitive people live with. Both have produced fascinating findings that can be useful to real-life HSPs. For example:
- On the Diathesis-Stress side, we know that sensitive people experience negative emotions more strongly and struggle to view emotions as temporary. Knowing that means knowing that emotional regulation techniques can be a lifesaver for even the healthiest HSP.
- On the Vantage Sensitivity side, however, we know that sensitive people actually become happy more easily and shift a positive mood quickly from even minor cues, like a heartwarming video.
These findings may not explain sensitivity itself, but they are far more useful to sensitive people, because they can be operationalized into simple tools and strategies that HSPs can use (like keeping a playlist of inspirational or heartwarming videos on Tiktok that you can scroll through when you’re struggling).
Key Differences Between the 4 Theories
If you want a cheat sheet, here are some of the key differences between the theories:
- Children vs. Adults: Most of the research on SPS has been conducted in adults. The other theories draw mainly on child development science.
- Psychology vs. Biology: SPS comes from work by psychologists, supplemented by neuroscience. On the other hand, Differential Susceptibility and Biological Sensitivity to Context combine developmental psychology with a heavy biology focus.
- Brain Wiring: SPS is the only model that proposes a brain-wiring explanation for sensitivity (“deeper information processing”). The others explain sensitivity in terms of evolution, biology, and nature vs. nurture. It’s possible for both to be correct.
- Nature vs. Nurture: Differential Susceptibility emphasizes “nature” (evolution and genes are the ultimate explanation). Biological Sensitivity to Context emphasizes “nurture” (childhood environment determines how sensitive you are). SPS does not, in and of itself, propose an answer to nature vs. nurture.
- Positive vs. Negative: Diathesis-Stress focuses on how sensitive people struggle in adverse environments, and Vantage Sensitivity focus on how sensitive people thrive and even outperform others in supportive environments. Differential Susceptibility definitively comprises both. The other theories may comprise both but it’s not their main focus.
- Widely Accepted: All four theories are still considered valid and all contain important contributions to understanding sensitivity. Researchers agree that all of these models refer to the same trait. It’s likely that all of them will eventually be combined under a single umbrella term — the dominant umbrella term is Environmental Sensitivity.
You can also view the four theories as simply being different in what they try to explain:
- Sensory Processing Sensitivity argues that sensitive people are “wired that way.”
- Differential Susceptibility argues that sensitive people are “born that way.”
- Biological Sensitivity to Context argues that sensitive people “become that way.”
- Diathesis-Stress and Vantage Sensitivity don’t necessarily try to explain what causes sensitivity. Instead, they offer a roadmap of the challenges to be overcome and advantages to be harnessed by sensitive people.
We Need All 4 Theories to Truly Understand Sensitivity
I’ve taken pains not to refer to these theories as “competing” theories; they’re not. While there is healthy scientific debate between the proponents of each one, they also incorporate each other’s findings and build on what the other theories offer. Ultimately, the sensitivity research community is, well, a pretty sensitive group of people who think deeply about each other’s work and support each other’s research.
The best way to view the four theories might be that we need all four to truly understand HSPs. Each one offers something valuable that is missing from the others. For example:
- Differential Susceptibility explains why evolution gave us sensitive people in the first place, and why it’s a useful trait for keeping our species alive. It’s the “Why” of sensitivity.
- Biological Sensitivity to Context explains how childhood environment shapes our sensitivity — both physically and psychologically. It’s the “How” of sensitivity.
- Sensory Processing Sensitivity explains the brain activity that comes with being sensitive, and what sensitive people are like as individuals — the experiences they have and the personality traits they tend to share. It’s the “Who” of sensitivity.
- Diathesis-Stress and Vantage Sensitivity explain the greatest struggles and greatest advantages of being a sensitive person. Together they offer a sort of user’s manual for how to thrive as an HSP — or at least, the fodder for psychologists and therapists to develop such a manual. They’re the “What next?” of sensitivity.
‘Environmental Sensitivity’ May Be the Most Important Theory of All
If all four theories describe the same trait, and all four teach something valuable about it, you might wonder why we don’t have a single term that encompasses all four. And, in a way, we do.
Environmental Sensitivity is a new term proposed by Michael Pluess in 2015. Rather than serving as a separate theory in its own right, Environmental Sensitivity is intended to serve as an umbrella that encompasses all the theories and models of sensitivity.
Environmental sensitivity proposes that:
- Some people respond more strongly to their environment than others
- Everyone is sensitive to a degree, and sensitivity is a continuum, where people can fall anywhere from low to average to high (that’s us HSPs!).
- These differences in sensitivity are the result of natural selection, but an individual person’s sensitivity is determined both by their genes and by their environment.
- Highly sensitive people struggle more with stressful conditions but benefit more from supportive conditions.
- Highly sensitive people likely process information more deeply than less-sensitive people
In other words, Environmental Sensitivity acknowledges the contributions of all four theories and gives them all a place under one roof, without “replacing” or killing off any of them. It’s sort of like how one therapist may lean on cognitive behavioral therapy while another may prefer somatic therapy, but at least they all have the word “therapy” and a common language to talk about new developments.
A few years ago, it was an open question whether Environmental Sensitivity would take off. As of 2023, however, it really is starting to become an umbrella term that unites the others. More and more papers use the term ”Environmental Sensitivity” as the definitive term for our trait, and all of the researchers behind the four theories — Aron included — have signed on to papers that use Environmental Sensitivity.
So What Is the Scientific Name for High Sensitivity?
Sensory Processing Sensitivity is not “the” scientific term for sensitivity, but neither are any of the other theories. The truth is, there simply is no one “official” scientific term for sensitivity (or HSPs), and there probably won’t be anytime soon.
However, the one widely accepted scientific term that includes all the major theories is Environmental Sensitivity. Increasingly, that’s the one I find myself using most.
As an HSP, you can use any of them that you like — or just sensitivity, responsiveness, or any other term of your choosing. The important thing is to learn from each of the theories, and always keep an open mind toward emerging findings that may conflict with — but ultimately improve upon — what we thought we knew.
After all, we are HSPs. And an HSP by any other name is still a deep thinker.
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