Loneliness (Cacioppo, Holt-Lunstad)
The painful feeling of a gap between the connection a person wants and the connection they have. Perlman and Peplau described it as the unpleasant experience of a network of relationships that falls short in quantity or quality. A person can be lonely in a full house, or alone for days and not lonely.
What drives it
Hawkley and Cacioppo describe loneliness as raising the wish to reconnect while also making a person more watchful for rejection and threat. Useful for identification because that watchfulness can make a lonely person read others as cold and pull back, which keeps the gap open.
How it shows
Work
Eating lunch alone and calling it efficiency. Feeling closer to colleagues on chat than to anyone at home. Going quiet in a team after being left out of one meeting.
Relationships
With children all day and no adult to tell about it at night. Scrolling through other parents' weekends. Turning down an invitation and then feeling hurt when nobody asks again.
Self
Notice whether the ache is for more people or for one person who knows you. Notice whether, when someone does reach out, you find reasons it doesn't count.
What tells it apart
Social isolation/alienation schema: The social isolation schema is a lasting belief, often from childhood, of being different and not fitting in any group. Loneliness may come and go with circumstances, such as a move or becoming a parent, and can happen to someone who has always felt they belong.
Major depression: Depression brings low mood and loss of pleasure across life and often includes loneliness. Loneliness alone is more likely when the low feeling centers on missing connection and lifts in good company, though each can feed the other.
Social anxiety: Social anxiety is fear of being judged in social situations, which keeps a person away from others. Loneliness is the felt gap itself and can come with no social fear at all, for example when there is no time or nobody nearby.
A test
Ask whether the person has someone they could call at ten at night with a problem, and how often in the past week they felt left out or without company. A gap between the connection they want and the connection they describe may point to loneliness, which the UCLA Loneliness Scale can measure.
Questions to carry
- Who did I want to tell about today, and was there anyone?
- What do I do when someone reaches toward me, and what do I tell myself about it?
How strong the research is
strong. In a meta-analysis of 70 prospective studies with about 3.4 million people followed for an average of seven years (Holt-Lunstad and colleagues, Perspectives on Psychological Science, 2015), loneliness went with 26% higher odds of death, social isolation with 29% and living alone with 32%, after adjusting for other factors. The studies were observational, so they show a consistent link and cannot rule out every other cause. The WHO Commission on Social Connection (2025) put loneliness at about one in six people worldwide. A scoping review of 133 studies of parents (Nowland and colleagues, Perspectives in Public Health, 2021) found evidence that parents' loneliness affects their own and their children's mental health, and said the evidence on which parents are most at risk was not conclusive. In Dutch national data for 2019 (Statistics Netherlands), 14.5% of single parents were often lonely, against 6.8% of people living with a partner and children.
Where it comes from
Daniel Perlman and Letitia Anne Peplau's definition, early 1980s. UCLA Loneliness Scale, Russell, Peplau and Ferguson, 1978. John Cacioppo and William Patrick, Loneliness: Human Nature and the Need for Social Connection, 2008. Louise Hawkley and John Cacioppo, 'Loneliness matters', Annals of Behavioral Medicine, 2010. Julianne Holt-Lunstad and colleagues, meta-analyses of 2010 and 2015