Loneliness Explained: What It Is, Why It Hurts, and How Common It Is

You can be lonely in a full office and content in an empty house, because loneliness tracks the connection you want, not the company you keep. The World Health Organization’s Commission on Social Connection, reporting in 2025, defines it as a negative emotional state that arises when your actual connection falls short of the connection you want. In the Commission’s estimate, about one in six people worldwide reported loneliness between 2014 and 2023, and teenagers reported it most often.¹

Loneliness is a feeling, not a head count

The WHO Commission on Social Connection treats loneliness as subjective and separates it from social isolation, the objective state of having few roles, relationships and contacts; it reports that the two are only weakly correlated. The gap behind loneliness can open in three places: too few connections, too little support from them, or interactions of poor quality.¹

That is why the two so often part company. Isolation can be counted from the outside, in households, contacts and meetings; loneliness is a comparison each person makes on the inside, between what they have and what they want.

As an illustration, a manager who moved cities for a new job spends every day in meetings and eats lunch with her team, yet has nobody to call on a Friday night: she is not isolated, but she may well be lonely. Her retired neighbor lives alone, gardens and sees his brother every Sunday: by some measures he is isolated, and he may not feel lonely at all.

1. Alone, not lonely: time on your own that you chose, which researchers call solitude, is not loneliness
2. Surrounded, still lonely: a busy office or a full family table can still leave the connection you want missing
3. The gap: loneliness is the painful difference between the connection you want and the connection you have

Being alone is different again. The Commission separates loneliness from the plain absence of other people and from solitude, time alone that you choose in order to rest, reflect or create. It also distinguishes transient loneliness, a response to events such as leaving home, a break-up or retirement, from chronic loneliness that persists, which some researchers define as lasting two years or more.¹

So judge loneliness by the gap, not by the calendar. A full diary does not rule it out, and a quiet week does not prove it. Two questions do more work: does the connection you have match the connection you want, and which part is missing, more people, more support or closer ones?

Why loneliness hurts: a signal that can backfire

Loneliness hurts because it works as a warning signal, in the account Louise Hawkley and John Cacioppo of the University of Chicago set out in a 2010 review. As hunger pushes you to eat, the pain of disconnection pushes you to repair relationships or find new ones, and most of the time it succeeds. The catch, in their model, is that feeling socially isolated registers as feeling unsafe. That sets off an unconscious watchfulness for social threat: lonely people tend to see the social world as more threatening than other people do, expect more negative encounters and remember more of the negative ones.²

loneliness is the social equivalent of physical pain, hunger, and thirst

As an illustration, a colleague answers your message with one word, and a lonely mind reads it as a snub rather than a busy afternoon. Holding back feels safer, the next invitation goes unanswered, and the gap widens. The signal meant to pull you toward people ends up holding you away from them.

The model is the authors’ synthesis of survey, laboratory and physiological studies, so treat it as a leading explanation rather than a settled fact. It does fit one practical finding they report: in a pooled analysis of randomized trials, programs that worked on how lonely people interpret social situations had larger effects on loneliness than programs offering more support, social skills training or more chances to meet, although only a handful of such trials existed.²

In practice, treat your reading of an ambiguous moment as a hunch to check rather than a verdict. Before deciding a friend has gone cold, try the dull explanation first; a short, low-stakes message often settles it.

What helps, in short

The WHO Commission found that promising approaches aimed at individuals and their relationships generally have small to moderate effects on loneliness. It judged psychological approaches the most promising, and it warned that many of the studies are of low quality.¹ That fits the trial comparison Hawkley and Cacioppo reported, although the Commission says the most effective approaches cannot yet be pinned down.

As an illustration, the manager from the example above might book a standing call each week with an old friend and join a weekly running group: small, repeatable contact rather than one big social push. Staying involved with other people also turns up in studies of how a sense of purpose grows.

Further reading

• 

  Loneliness: Human Nature and the Need for Social Connection

  by John T. Cacioppo, William Patrick

  Cacioppo, whose model of loneliness as a warning signal this article explains, sets out the research behind it for general readers.

As an Amazon Associate WiserHours earns from qualifying purchases.

How common is loneliness? It depends on the question

Published estimates of the prevalenceprevalence: The share of a population who have a given condition at a point in time or across a set period. Every prevalence figure depends on the case definition behind it: loosen or tighten the criteria for counting as a case and the figure moves with them.Full entry in the glossary of loneliness differ widely, and US figures run several times higher than the WHO’s global one. Much of that spread likely comes from the question each survey asked and the threshold it used: the WHO Commission notes that survey questions differ so widely that findings are hard to compare, and its own estimate aims to count only people who feel very lonely. It pooled surveys covering most of the world’s countries; the main one, by Meta-Gallup, asked “In general, how lonely do you feel?” and counted people who answered very or fairly lonely, while others asked how often people had felt lonely over a set week, month or year, or used short questionnaires.¹

The US figure rests on a different tool. The Surgeon General’s 2023 advisory says about one in two American adults reported loneliness, citing, among other sources, surveys commissioned by the insurer Cigna.³ Those surveys used the full-length UCLA Loneliness Scale and counted anyone scoring 43 or more as lonely.⁴ Its questions include “How often do you feel that people are around you but not with you?”, each answered always, sometimes, rarely or never. Scores can run from 20 to 80, so the cut-off sits below the midpoint, and in a peer-reviewed report on Cigna’s large 2018 online survey, weighted to match US adults, funded by Cigna and with Cigna employees among the authors, the average respondent scored just above it.⁵

Neither figure is simply wrong; they measure different things. A single direct question depends on people admitting to loneliness, which the Commission notes stigma can discourage, while a long scale with a cut-off below its midpoint is likely to cast a much wider net. On whether loneliness is rising, the Commission says earlier data are too limited to tell.¹

Is loneliness as harmful as smoking 15 cigarettes a day?

That comparison is not a measured result about loneliness. The US Surgeon General’s 2023 advisory states that lacking social connection carries a risk of early death similar to smoking “up to 15 cigarettes a day”, citing a 2017 paper by the psychologist Julianne Holt-Lunstad and colleagues.³ The comparison itself goes back to a chart in her team’s 2010 meta-analysismeta-analysis: A study that combines the results of earlier studies on the same question into one overall estimate. Pooling makes the estimate more precise, but it cannot repair the studies it pools: a meta-analysis of surveys is still survey evidence.Full entry in the glossary, which set the link between weak social relationships and earlier death beside separate estimates for smoking, drinking and obesity.⁶

The study

Moderate evidence

Where the cigarette comparison began: a 2010 pooling of 148 studies

The team pooled studies that recorded people’s social relationships and then tracked who died. People with stronger relationships had about 50 percent higher odds of surviving the follow-up period than people with weaker ones. A chart then set this result beside other meta-analyses: one bar showed smoking fewer than 15 cigarettes a day, and the overall estimate for social relationships sat a little below it.⁶

The pattern is consistent, but it is observationalobservational study: A study in which researchers record what people already do or are exposed to, rather than assigning anyone to anything. It can show that two things go together, not that one causes the other, because the groups being compared may differ in other ways as well.Full entry in the glossary. As the authors note, nobody can randomly assign people to lose their friends, and people nearer death may already have less support, so illness drifting people out of social life could explain part of the link.⁶

Read closely, the chart supports less than the slogan. Most of the pooled studies measured social networks, marriage, support or involvement in community life, and only a handful measured loneliness itself. The smoking bar came from a different meta-analysis of different people, so setting the two side by side is a rough benchmark, not a head-to-head test. That bar also covered smoking fewer than 15 cigarettes a day, which makes “up to 15” fair and “15 a day” an overstatement. And the review reports odds, not how many extra deaths the link adds up to.⁶

Reviews that isolate loneliness find a smaller link. A 2015 meta-analysis by the same team, seen by us only as an abstract, linked loneliness to about a quarter higher odds of death after adjusting for other factors.⁷ A 2023 review of cohort studies led by Fan Wang, also seen only as an abstract, put the figure for loneliness at about 14 percent higher risk, smaller than for social isolation.⁸ Neither abstract gives absolute numbers, so neither says how many extra deaths these mean.

Whether loneliness causes harm is still argued. The WHO Commission judges the link between social disconnection and death probably causal, because the evidence meets standard criteria for inferring cause when experiments are impossible. Yet a large UK genetic study it describes found possible causal links between loneliness and fewer than a quarter of the diseases examined, including depression, with little causal evidence for cardiovascular disease or type 2 diabetes.¹

The fair version to pass on is narrower than the headline: in long-term studies, weak social ties carried a risk in the range of smoking fewer than 15 cigarettes a day, which is reason enough to take lasting loneliness seriously, as the WHO does. It is not a measured, cigarette-sized dose of harm from feeling lonely.

Where to turn if loneliness comes with low mood or danger

Loneliness on its own is not a medical diagnosis. The UK’s NHS says most people feel it at some point, that there is no shame in it and that it can pass. For everyday steps it suggests keeping in regular touch with people, joining a group built around something you enjoy and reaching out to others who may be lonely, and it lists free UK services such as befriending networks and Silverline, a phone line for people over 55. It also warns that loneliness which is very severe or goes on for a long time might raise the risk of anxiety, low mood or depression.⁹ We have ordered the routes by urgency. The routes come from NIMH, the US National Institute of Mental Health, or from the NHS; the urgency tiers, the routine step and the notes on other countries are our own general guidance.

If you are in danger now, meaning you are thinking about suicide or self-harm or feel unable to keep yourself safe: for readers in the US, NIMH directs people to the 988 Suicide and Crisis Lifeline (phone or text 988, or chat online) and names 911 or the nearest emergency room for a life-threatening situation.¹⁰ For UK readers, the NHS lists 999 and A&E as the routes if you do not feel able to keep yourself, or someone else, safe, and Samaritans (116 123) take calls free of charge. In England, urgent needs that are not emergencies can go to NHS 111, whose phone line has a mental health option and which also works online, or to an urgent GP appointment.¹¹ Readers in other countries should use their local emergency number.

If low mood has settled in, act within a few days or weeks. The UK’s NHS, in guidance last reviewed in 2023, advises seeing a GP when symptoms of depression, such as hopelessness or lost interest in things, are there most of the day, every day, for more than 2 weeks.¹² Elsewhere, your usual doctor or a primary care clinic is the first stop.

If loneliness has dragged on for months but your mood is holding up, it is reasonable to mention it at a routine check-up. NIMH notes that a primary care provider can screen for mental health problems and refer people to a mental health professional.¹⁰

The bottom line

Ask what is missing, whether people, support or closeness, rather than counting company: loneliness measures a gap, not a crowd. The WHO puts it at about one in six people worldwide, and much higher figures often reflect broader survey questions. Take lasting loneliness seriously, and pass on the cigarette comparison, if at all, as a rough benchmark for social ties in general rather than a dose.