An unpleasant emotional reaction to feeling alone is loneliness. Another term
  for loneliness is social pain, which is a psychological process that drives
  people to look for social interactions. It is frequently linked to a feeling
  of estrangement and detachment. While loneliness and solitude overlap, they
  are not the same thing. Being alone is the definition of loneliness; not
  everyone who experiences solitude feels alone. Loneliness is a subjective
  feeling that can occur in social situations as well. Therefore, there is a
  difference between feeling lonely and actually being alone. Both short-term
  (state loneliness) and long-term (chronic loneliness) loneliness are possible.
  It can be excruciating and agonizing in either scenario.
  Loneliness can have many different reasons. Genetic predisposition, cultural
  influences, a dearth of meaningful interactions, a major loss, an
  over-reliance on passive technologies (especially the Internet in the
  twenty-first century), or a self-perpetuating attitude are all potential
  causes of loneliness. According to research, lonely persons can be found in
  all spheres of society, including successful professionals and those in
  marriages and other committed partnerships. The majority of people have been
  lonely at some point in their life, and others experience it frequently.
  Additionally, loneliness has a variety of impacts. Positive outcomes, such as
  a greater emphasis on the quality of one s relationships, have been linked to
  transient loneliness, or loneliness that lasts only a brief while.
  Chronic loneliness, defined as loneliness that lasts for a considerable period
  of time, is typically associated with detrimental outcomes, such as an
  increased risk of obesity, substance abuse disorders,
  depression, cardiovascular disease, high blood pressure, and high cholesterol.
  Prolonged isolation is also linked to a higher chance of passing away and
  thoughts of suicide.
  Antidepressants and therapy are two medical therapies for loneliness.
  Increasing social connection through activities like exercise or religious
  pursuits in groups, reconnecting with former coworkers or acquaintances, and
  strengthening ties to the community are all common social
  therapies
  for loneliness. Pet ownership and loneliness-designed technologies, including
  meetup services or social robots, are further social treatments for loneliness
  (although the effectiveness of some technologies to combat loneliness is
  contested). 
Causes of Loneliness
  Existential: For a long time, loneliness was thought to be a
  condition that everyone experiences, at least somewhat. According to this
  viewpoint, loneliness is unavoidable to some extent since no one can always
  satiate their innate need for connection due to the constraints of human life.
  Scholars such as Michele A. Carter and Ben Lazare Mijuskovic have penned books
  and essays tracing the history of the existential perspective and its
  proponents. In this context, Thomas Wolfe s 1930 article God s Lonely Man is
  widely debated. In it, Wolfe argues that while everyone believes they are
  lonely in a way that is unique to them, in reality, loneliness affects
  everyone occasionally. Although existentialists acknowledge that reducing
  loneliness can be desirable, they tend to doubt that such attempts would ever
  be completely successful, viewing some degree of loneliness as both inevitable
  and even advantageous because it can help individuals appreciate life s joys.
  Cultural: Loneliness is said to be caused by culture in two
  different ways. Loneliness among migrants might arise from missing their
  native culture. Research has indicated that this effect can be particularly
  pronounced for Asian students from collectively culturally rich countries when
  they attend universities in more individualist English-speaking nations.
  Another way to look at culture and loneliness is to say that since the
  Enlightenment, when individuality began to take precedence over more
  traditional communal norms, loneliness may have been exacerbated by western
  civilization.
  Lack of Meaningful Relationships: A lot of people find that
  their family of origin did not provide the kind of relationships based on
  trust that are necessary to create a lifetime memory of a loved one, even
  after they have passed away. Parenting practices, cultural norms, mental
  health conditions like
  Visit Example
  and violent family situations can all contribute to this. There is also
  religious shunning at times.
  This affects people s capacity to relate to others, esteem themselves, and
  know themselves—or to do so with considerable difficulty.
  The conventional medical or psychiatric advice that advises going out and
  seeing friends and family and socializing ignores all these considerations and
  many more. When there is no one to relate to and you are unable to connect
  without the necessary abilities and information, this isn t always achievable.
  A person may eventually get apathetic or disillusioned due to repeated
  setbacks, rejections, or disappointments brought on by a lack of interpersonal
  skills.
  It is challenging to find new ways to connect people with each other at a time
  when a lot of people s attention is focused on electronic devices, as the rate
  of loneliness among people of all ages is rising annually and is higher among
  the elderly. Loneliness has been shown to have negative physical and
  psychological effects.
  Loss of a relationship: One extremely typical, but frequently
  transient, effect of ending a relationship or losing a loved one is
  loneliness. A grieving process usually begins with the loss of a significant
  other; in this case, even when one is surrounded by people, loneliness may set
  in. People who move away for employment or school may experience homesickness
  in addition to loneliness as a result of the disruption of their social
  circle.
  Contextual: Loneliness can result from a variety of
  circumstances and occurrences, particularly when combined with specific
  personality qualities in vulnerable people. For instance, living in an area
  with a low population density, where there are fewer people to socialize with,
  can make an extroverted and highly social person feel lonely. Events that one
  might typically expect to lessen loneliness can sometimes actually make it
  worse, such as having a child (if there is severe postpartum depression) or
  getting married (especially if the marriage proves to be unstable, overly
  disruptive to previous relationships, or emotionally cold.) Loneliness can be
  exacerbated not only by outside circumstances but also by mental health issues
  such as
  anxiety
  and persistent depression.
  Self perpetuating: Chronic loneliness can lead to a variety
  of maladaptive social cognitions, including hypervigilance and social
  awkwardness, which can make it more difficult for a person to form new
  relationships or keep up ones that already exist. Though it is not always
  successful, research has shown that the most effective strategy to intervene
  to lessen loneliness is through treatment that aims to address this
  maladaptive cognition.
  Social Contagion: Like a disease, loneliness can spread among
  social groupings. The maladaptive thinking that frequently follows long-term
  loneliness is the mechanism behind this. A man may get more lonely if he loses
  a buddy for any reason, which could lead to the development of maladaptive
  thought patterns like excessive neediness or mistrust of other friends. hence,
  should he go on to break up with his remaining buddies, resulting in an
  additional loss of human connection. There is now a cascade of loneliness as
  those other pals start to feel more alone as well.
  However, research has shown that this contagion effect is not always present—a
  slight increase in loneliness is not necessarily the reason for the
  maladaptive thought patterns. Additionally, people may make new acquaintances
  or strengthen existing ones after losing a friend.
  Internet: Research, particularly those that use data from the
  1990s, when internet use became commonplace, have tended to reveal a moderate
  link between substantial internet use and loneliness. Studies looking into
  whether the link is just the result of lonely people being more drawn to the
  internet or whether the internet might genuinely promote loneliness have
  produced contradictory results. According to the displacement hypothesis, some
  people decide to spend less time online and less time interacting with others
  in person. The potential of the internet to empower people and promote contact
  may outweigh the risks associated with excessive use, which can lead to
  anxiety, sadness, and loneliness. 
  Molecular Biology: According to smaller, earlier studies,
  loneliness may be 37–55% inherited. The first genome-wide association study on
  loneliness, conducted in 2016, discovered that the heritability of loneliness
  is substantially lower, ranging from 14% to 27%. This implies that although a
  person s genes may influence their level of loneliness, personal experiences
  and environmental factors have a greater influence.
Types of Loneliness
  Social and emotional loneliness are the two main categories of loneliness.
  Robert S. Weiss articulated this distinction in his landmark 1973 book
  Loneliness: The Experience of Emotional and Social Isolation. People who work
  to treat or better understand loneliness have tended to treat these two types
  of loneliness separately, though this is far from always the case. This is
  because Weiss believed that "both types of loneliness have to be examined
  independently, because the satisfaction for the need of emotional loneliness
  cannot act as a counterbalance for social loneliness, and vice versa."
  Social loneliness
  The loneliness that results from having a small social circle is known as
  social loneliness. They might not believe they are a part of a group or that
  they have allies or friends they can turn to in difficult times.
  Emotional loneliness
  An inability to form meaningful, caring relationships with other people leads
  to emotional loneliness. Weiss connected attachment theory to his idea of
  emotional loneliness. Humans require strong bonds, which can be satisfied by
  close friends, but they are also frequently satisfied by parents and other
  close family members, as well as later in life by love partners.
  Enrico DiTommaso and Barry Spinner divided emotional loneliness into two
  categories in 1997: romantic loneliness and family loneliness. In contrast to
  social loneliness, which did not raise mortality, a 2019 study indicated that
  emotional loneliness greatly raised the risk of death for older persons living
  alone.
  Family loneliness
  People who believe they don t have strong relationships with their family
  members experience familial loneliness. In contrast to romantic or social
  loneliness, only family loneliness was linked to a higher incidence of
  self-harm, according to a 2010 study including 1,009 students.
  Romantic Loneliness
  Adults and teenagers who do not have a close relationship with a romantic
  partner may experience romantic loneliness. According to
  psychologists
  , developing a committed love relationship is an important responsibility for
  young adults, but many are putting it off until their late 20s or later. As
  long as they experience emotional closeness in their connection, persons in
  romantic partnerships typically report feeling less lonely than single people.
  Romantic loneliness can still exist in relationships where one spouse is
  emotionally distant or unstable.
  Distinguishing between social isolation and loneliness
  Being socially isolated (a loner, for example) and feeling lonely are two
  quite different things. Specifically, loneliness can be understood as the
  difference between one s required and actual amounts of social connection,
  whereas isolation is just the absence of social interaction. Therefore,
  loneliness is a multifaceted and subjective emotion; loneliness is experienced
  by an individual only if they believe they are alone. Both being alone and
  being in the center of a throng can make someone feel lonely. A person
  experiences loneliness when they believe they should be in more social
  situations or in situations of a particular kind or caliber that are not
  readily available to them. When at a party, someone may feel lonely because
  they aren t interacting with people.On the other hand, despite the fact that
  no one else is present, a person can remain alone and not feel lonely if they
  have no desire to socialize. There have also been arguments made for the idea
  that everyone has a certain ideal degree of social engagement. An individual
  may experience emotions of loneliness or overstimulation if they engage in too
  little or too much social interaction.
  For some people, solitude might be beneficial. According to one study,
  spending time by oneself can enhance one s cognitive state, including focus,
  even if it also tends to lower mood and exacerbate feelings of loneliness. One
  could argue that some people look for isolation in order to find a more vital
  and meaningful life. Moreover, people s moods tended to dramatically improve
  after the alone time. Aside from these benefits, solitude is also linked to
  religious experiences, identity formation, and other beneficial growth
  experiences. One example of this is the use of solitude in rites of passage
  for adolescents.
  Transient vs. chronic loneliness
  The temporal viewpoint is the subject of another significant loneliness
  typology. In this sense, loneliness might be classified as either temporary or
  permanent.
  Transient loneliness is a transient emotion that may usually be quickly
  resolved. Severe loneliness is more enduring and difficult to overcome.A
  person experiencing temporary loneliness can be unwell and unable to interact
  with friends. Reducing loneliness would be simple for the person after they
  recovered. Chronic loneliness is the state in which a person experiences
  long-term emotions of loneliness, regardless of whether they are with friends
  or at a family reunion.
  Loneliness as a human condition
  Individuality is seen by existentialists as the fundamental aspect of what it
  is to be human. Every human being is born alone, lives their entire existence
  as an individual, and passes away alone. The human condition is to learn to
  live with some degree of grace and satisfaction, to cope with this, to accept
  it.
  Some philosophers, like Sartre, hold that loneliness is an inherent aspect of
  the human experience due to the conflict between people s consciousness
  seeking purpose in existence and the universe s nothingness and solitude. This
  idea is known as epistemic loneliness. On the other hand, some existentialist
  philosophers contend that loneliness is just the experience of feeling
  detached from human interaction and creation, which involves humans actively
  engaging with the universe and one another.
  Loneliness and It’s Impact on one’s Mental Health
  Since loneliness and
  depression
  have been connected, loneliness increases the chance of suicide. Loneliness
  was examined in an analysis of over 4,000 persons over 50 who participated in
  the English Longitudinal Study of Ageing (ELSA). Within a year, nearly one in
  five of those who said they were lonely showed signs of depression. Émile
  Durkheim defined egoistic suicide as mostly caused by loneliness, notably the
  incapacity or reluctance to live for others, i.e., for friendships or
  altruistic ideals. Loneliness is a significant trigger for drinking and
  depression in adulthood. Individuals who lack social support may experience
  poor sleep, which can lead to a reduction in their ability to heal themselves.
  Although the long-term effects of prolonged periods of loneliness are poorly
  understood, it has been observed that individuals who are alone or suffer from
  loneliness for extended periods of time enter a state known as "ontological
  crisis" or "ontological insecurity," in which they are unsure of whether they
  exist at all or if they do, exactly who or what they are. This state causes
  them to experience intense mental pain and suffering.
  Lack of social ties in kids is closely associated with a number of antisocial
  and self-destructive behaviors, the most prominent of which are aggressive and
  delinquent behaviors. Loneliness frequently hinders memory and learning in
  both adults and children. Its interference with sleep cycles can seriously
  impair one s capacity to carry out daily tasks.
  As a cluster of symptoms, pain,
  depression, and exhaustion may have similar risk factors. The development of the pain,
  sadness, and fatigue symptom cluster over time was shown to be at risk for
  loneliness, according to two long-term studies conducted on distinct
  populations. The health hazards associated with loneliness are also
  highlighted by these statistics; those who experience pain, despair, and
  weariness in addition to serious disease are at a higher risk of poor health
  and mortality.
  Suicidal ideas, suicidal thoughts, and suicidal acts can all be brought on by
  loneliness. It is challenging to pinpoint the precise degree to which
  loneliness contributes to suicides, though, as there are usually a number of
  possible reasons. Dr. Jeremy Noble writes, "You don t have to be a doctor to
  recognize the connection between loneliness and suicide" in an essay for the
  American Foundation for Suicide Prevention. Suicidal thoughts and attempts
  increase with the intensity of loneliness. There are effects on all levels of
  society from the loneliness that leads to suicidal thoughts.
  Elderly individuals may also experience extreme loneliness, which might
  provoke suicidal or self-harming ideas in them. Some nations seem to have a
  large percentage of suicides among their senior inhabitants, whereas other
  nations have a noticeably greater suicide rate among middle-aged men.
  Loneliness can be exacerbated by retirement, ill health, the death of a
  significant other or other family members or friends. It can be challenging to
  pinpoint older adults who commit suicide as a result of loneliness. They
  frequently have no one with whom to share their loneliness and the ensuing
  hopelessness. To hasten death and spare themselves the agony of loneliness,
  people can give up food, change the dosages of their meds, or decide not to
  treat a sickness.