A team of researchers led by Byungkyu Lee, an assistant professor of sociology at New York University, published findings in February 2026 that many people will recognize on a gut level: the difficult people in your life are not just emotionally exhausting. They may be accelerating how fast your body ages at a cellular level. The study, which appeared in the Proceedings of the National Academy of Sciences (PNAS), drew on data from 2,345 adults in Indiana whose ages ranged from 18 to 103. Researchers analyzed both their social networks and biological samples to examine whether strained relationships leave a measurable mark on the body – and found that they do.
The research team coined a specific term for the people at the center of their investigation: “hasslers.” This is not slang for someone who occasionally annoys you. The study defined hasslers as people within a close social network who “often” cause problems or make life harder. They can be family members, friends, coworkers, or neighbors – anyone who is a consistent source of friction rather than support. The researchers then used tools called epigenetic clocks – biological measures that read DNA to estimate how fast a person’s body is aging – to track whether those stressful relationships show up in the body’s own record-keeping.
What Biological Aging Actually Means
Most of us think about age in one way: the number of years since we were born. That is called chronological age. But your body also has its own internal clock, and it does not always run at the same speed as the calendar.
Biological aging is a process involving the gradual accumulation of unrepaired molecular damage, leading to progressive declines in physiological function. Importantly, individuals vary substantially in how fast this process unfolds – due to genetic factors as well as environmental and social ones. Two people born in the same year can have biological ages that differ by a decade or more.
The tool researchers use to measure this is called an epigenetic clock (ep-ih-jih-NET-ik). These are not physical clocks, of course – they are algorithms that analyze something called DNA methylation. DNA methylation is a natural chemical process that changes how genes are turned on or off, without altering the underlying genetic code. By tracking these chemical tags, scientists can estimate a person’s biological age – which reflects how old their cells act, rather than how old they are in years.
The Lee study used two specific epigenetic clocks – GrimAge2 and DunedinPACE – to assess biological aging. These tools look at DNA methylation patterns to estimate both biological age relative to chronological age and the pace at which aging is occurring. The DunedinPACE clock, in particular, measures the speed of aging rather than just the accumulated total – think of it as tracking not how old someone is, but how fast they are getting there.
What the PNAS Study Found
The PNAS study analyzed the biological ages and survey data of 2,345 people ranging in chronological age from 18 to 103 years old. Participants were asked during interviews to identify people in their personal networks who regularly made their lives more difficult. They were asked how often certain individuals in their lives “hassled them, caused problems, or made life difficult” over the previous six months. Saliva samples were then collected to provide the biological data that allowed the epigenetic clock analysis.
Nearly 29 percent of participants reported at least one “hassler” – defined as a network member who frequently created problems, caused stress, or made life difficult. That figure alone is striking. It suggests that roughly three in ten adults are navigating at least one consistently draining relationship in their inner circle, not an occasional difficult day but an ongoing social stress.
The study found that for every additional hassler in someone’s life, the impact on their health worsened. Specifically, researchers estimated that the pace of aging increases by 1.5 percent, or about nine months of biological aging, per hassler. So if you had three hasslers in your life, you would be – biologically speaking – almost two and a half years older than someone the same age as you with none.
A pace of 1.5 percent might not sound significant, but the effects accumulate quickly across multiple stressful relationships. One hassler means that while you chronologically turn one year older at your next birthday, biologically you would age 1.015 years. With three difficult people in your life, that number ticks up to 1.045.
The Family Factor
One of the more specific findings from the research involves where the aging effect is strongest. Not all difficult relationships carry equal weight – and the data reveals that who the hassler is matters enormously.
The researchers found evidence that the type of relationship matters. Family members who act as hasslers showed the strongest association with accelerated aging. Lead author Dr. Byungkyu Lee explained this by pointing to the “stickiness” or inescapability of certain roles – because family ties are often embedded in obligations and shared spaces, they are difficult to escape. This inescapability may trap people in repeated stressful interactions.
The data showed that the presence of any kin-related hassler was linked to 1.100 additional years of biological aging, while non-kin hasslers were associated with 0.833 additional years. That gap is meaningful. Stress from a parent, child, or sibling carries a heavier biological toll than stress from a friend or neighbor – likely because there is less ability to simply walk away.
Family hasslers – especially parents or children – were more detrimental, likely because there is a sense of obligation, dependence, a shared living space, or some combination of the three. Interestingly, while other family and non-family hasslers had a negative impact on participants’ biological age, spouses did not show the same pattern.
Researchers found that having a hassler as a spouse does not carry the same negative biological impact. It could be that the positives of shared routines, resources, and emotional intimacy offset the stress in a way that other relationships cannot. That nuance matters. It suggests that when stress and support exist together in the same relationship – as they often do in marriages – the body may process that differently than pure, unrelenting friction from someone you cannot easily support or be supported by.
For readers thinking about their own relationships and what makes them last, this research adds a meaningful layer: it is not just who you are with, but whether those around you genuinely leave you better or worse off.
How Social Stress Gets Under Your Skin
Understanding why difficult social relationships biological aging connection exists means looking at what stress does to the body over time. The short answer: chronic stress is hard on every major system.
Scientists believe chronic interpersonal stress affects the body through several biological pathways. Repeated stress activates the hypothalamic-pituitary-adrenal (HPA) axis – a chain reaction between the brain and the adrenal glands – increasing the release of hormones such as cortisol. Over time, this sustained stress response contributes to inflammation, immune changes, and accelerated aging.
Research suggests that negative social ties may accelerate biological aging by mimicking the harmful effects of traditional chronic stressors, such as financial strain or workplace stress, and contribute to increased inflammation, compromised immune function, and elevated risk for cardiovascular and other diseases. Think of it this way: the body does not care whether the stress is coming from debt, a difficult job, or a family member who makes every interaction harder. The physiological response is largely the same.
The cumulative mental and physical strain that stress causes over time – called the allostatic load – can negatively affect the immune, cardiovascular, and metabolic systems. Allostatic load (al-oh-STAT-ik) is simply the accumulated wear and tear on the body from ongoing stress. Once that load becomes chronic rather than occasional, the body struggles to recover between stressors.
The study also found that individuals with more hasslers tended to have worse health outcomes overall, including higher levels of depression, anxiety, and poorer self-rated health. The biological aging effects, in other words, do not exist in isolation. They show up alongside a broader picture of declining health. This is the stress and aging science translated into real consequences for how people feel day to day.
Who Is Most Affected
The PNAS aging study found that some groups are more likely to report hasslers in their lives than others. This is not random – and understanding the pattern helps explain why stress and poor health so often show up together in the same populations.
Some people are more likely to have hasslers in their lives than others. The research found that the number was higher for women, daily smokers, people in poorer health, and people who have had difficult childhoods.
One explanation offered by Dr. Lee is that people who already face more stress or fewer resources may have less ability to avoid, buffer, or disengage from difficult relationships, so chronic strain becomes more embedded in everyday life. Put plainly: when you have fewer options for stepping away from a difficult person – because of finances, family obligation, living arrangements, or shared responsibilities – you absorb more of the damage.
These patterns suggest that social stress may compound existing health vulnerabilities, creating a cycle in which individuals facing adversity also experience more difficult social environments. For parents – especially mothers – who are often managing overlapping obligations to children, partners, and extended family members, this cycle is not an abstraction. It is the lived texture of a difficult week multiplied across months and years.
Can Toxic Friendships Speed Up the Aging Process?
This is one of the most common questions people ask when they come across this research – and the answer, based on the PNAS data, is: yes, the evidence points that way, though with important caveats.
Can toxic friendships speed up the aging process? The study’s findings suggest they can. Scientists found that individuals who report having “hasslers” in their lives tend to experience a faster pace of cellular aging and an elevated risk for various health problems. Friends qualify as hasslers in this research when they consistently create friction, cause problems, or make life harder – not when they occasionally have a bad day.
But it is important to understand what this research does and does not prove. While the study provides robust data, there are potential misinterpretations to avoid. Because the research is observational, it cannot prove that hasslers directly cause accelerated aging. There are alternative explanations – such as the possibility that people who are biologically aging faster become more irritable and provoke negative interactions.
This is a critical distinction. The finding is an association, not a proven cause-and-effect chain. That said, as Dr. Byungkyu Lee noted, “What was most striking was that negative social ties were linked not just to self-reported stress or mental health, but to molecular measures of biological ageing.” Finding the same signal in the DNA – not just in how people report feeling – gives the findings considerably more weight than a standard self-reported wellness survey.
As Kathy Richardson, PhD, assistant professor of clinical mental health counseling at Lebanon Valley College, put it: “Biological aging is a cumulative process, and small amounts can turn into larger aging gaps over time.” That framing is useful. The 1.5 percent figure per hassler sounds small in isolation. But if difficult relationships are present for years, that gap compounds – and the cumulative effect becomes harder to ignore.
The Question Nobody Wants to Answer: What Do You Do?
Here is where the research gets genuinely difficult, because the obvious solution – cut out everyone who causes you stress – is not realistic for most people, and may not even be the right framing.
Avoiding difficult people entirely is not always possible, particularly when they are family members or colleagues. However, experts recommend practical strategies such as setting clear boundaries, limiting exposure when possible, and prioritizing supportive relationships.
Boundaries, in this context, is not a wellness buzzword. It is a harm-reduction strategy backed by biological evidence. If a specific relationship is reliably activating your body’s stress response – releasing cortisol, raising inflammation – then reducing contact with that person is a health intervention just as much as quitting smoking or cutting back on sugar.
As Dr. Lee explained: “These findings suggest that promoting healthy aging requires not only strengthening supportive ties, but also reducing chronic interpersonal stress within close relationships.” The goal is not a frictionless social life. The goal is a healthier ratio – more relationships that replenish you than drain you.
Researchers stress that strong social connections are known to improve health, lower the risk of cognitive decline, and even increase longevity, while loneliness and social isolation carry their own serious health risks. So this is not a case for retreating from relationships altogether. Research clearly shows that the absence of supportive ties is not equivalent to the presence of negative ones. Both matter – just in different directions.
When cutting contact is impossible – as it often is with parents or adult children – the research points toward managing the intensity and frequency of stressful interactions rather than eliminating them. That can mean shorter visits, a buffer of supportive relationships to offset the damage, or professional support to process the ongoing strain.
Read More: What’s the Ideal Age Gap for a Lasting Relationship?
What This Means for You
The headline finding from this PNAS study on social relationships and biological aging is straightforward: the difficult people in your life are not just wearing on your patience. They may be wearing on your cells. Each persistent hassler in your close network is associated with roughly nine months of additional biological age and a 1.5 percent faster rate of aging – effects that compound the more difficult relationships you carry at once. That is a meaningful enough signal to take seriously, even as the research acknowledges it cannot yet establish direct causation.
What the science does clearly support is this: the quality of your relationships is not just an emotional concern – it is a physical health one. If you have been tolerating a relationship that costs you more than it gives, this research offers a different way to think about why you feel so tired. Protecting your time, your energy, and your close social circle from chronic interpersonal stress is not selfish. According to the data from Lee and his colleagues at New York University, Utah State University, the University of South Florida, the University of Michigan, and Indiana University, it may be one of the more underrated things you can do for your long-term health. Being strategic about who gets regular access to your life – and how much of it – turns out to be a question worth taking as seriously as sleep, nutrition, or exercise.
Disclaimer: This article was created with AI assistance and edited by a human for accuracy and clarity.