We looked at studies published worldwide since 1945 and found 144 qualitative sources conceptualising loneliness across the adult life course. In these studies, three types of loneliness were identified: social loneliness, emotional loneliness and existential loneliness. Social loneliness refers to the perceived deficit in the quality of social connections.
Social loneliness was conceptualised in studies of young people, paid and unpaid work, healthcare, place, migrant and cultural groups, and older people and health and social, communities, health and illness, rural and urban environments, and migrant, cultural and gender groups.
Emotional loneliness refers to feelings which arise from loss of meaningful relationships that meet a deeply felt need to be recognised and belong. Studies reporting on emotional loneliness across the life course included work on loss of a spouse, physical and mental health conditions, family contexts and place.
Existential loneliness refers to an experience of feeling entirely separate from other people, often when confronted with traumatic experiences or mortality. Studies including people with mental illness, older population groups and in psychotherapy described existential loneliness.