Loneliness is a complex and usually unpleasant emotional response to isolation. Loneliness typically includes anxious feelings about a lack of connection or communication with other beings, both in the present and extending into the future. As such, loneliness can be felt even when surrounded by other people. The causes of loneliness are varied and include social, mental, emotional and physical factors.
Research has shown that loneliness is prevalent throughout society, including people in marriages, relationships, families, veterans, and those with successful careers. It has been a long explored theme in the literature of human beings since classical antiquity. Loneliness has also been described as social pain--a psychological mechanism meant to motivate an individual to seek social connections. Loneliness is often defined in terms of one's connectedness to others, or more specifically as "the unpleasant experience that occurs when a person's network of social relations is deficient in some important way." 
People can experience loneliness for many reasons, and many life events may cause it, such as a lack of friendship relations during childhood and adolescence, or the physical absence of meaningful people around a person. At the same time, loneliness may be a symptom of another social or psychological problem, such as chronic depression.
Many people experience loneliness for the first time when they are left alone as infants. It is also a very common, though normally temporary, consequence of a breakup, divorce, or loss of any important long-term relationship. In these cases, it may stem both from the loss of a specific person and from the withdrawal from social circles caused by the event or the associated sadness.
The loss of a significant person in one's life will typically initiate a grief response; in this situation, one might feel lonely, even while in the company of others. Loneliness may also occur after the birth of a child (often expressed in postpartum depression), after marriage, or following any other socially disruptive event, such as moving from one's home town into an unfamiliar community, leading to homesickness. Loneliness can occur within unstable marriages or other close relationships of a similar nature, in which feelings present may include anger or resentment, or in which the feeling of love cannot be given or received. Loneliness may represent a dysfunction of communication, and can also result from places with low population densities in which there are comparatively few people to interact with. Loneliness can also be seen as a social phenomenon, capable of spreading like a disease. When one person in a group begins to feel lonely, this feeling can spread to others, increasing everybody's risk for feelings of loneliness. People can feel lonely even when they are surrounded by other people.
A twin study found evidence that genetics account for approximately half of the measurable differences in loneliness among adults, which was similar to the heritability estimates found previously in children. These genes operate in a similar manner in males and females. The study found no common environmental contributions to adult loneliness.
There is a clear distinction between feeling lonely and being socially isolated (for example, a loner). In particular, one way of thinking about loneliness is as a discrepancy between one's necessary and achieved levels of social interaction, while solitude is simply the lack of contact with people. Loneliness is therefore a subjective experience; if a person thinks they are lonely, then they are lonely. People can be lonely while in solitude, or in the middle of a crowd. What makes a person lonely is the fact that they need more social interaction or a certain type of social interaction that is not currently available. A person can be in the middle of a party and feel lonely due to not talking to enough people. Conversely, one can be alone and not feel lonely; even though there is no one around that person is not lonely because there is no desire for social interaction. There have also been suggestions that each person has their own sweet spot of social interaction. If a person gets too little or too much social interaction, this could lead to feelings of loneliness or over-stimulation.
Solitude can have positive effects on individuals. One study found that, although time spent alone tended to depress a person's mood and increase feelings of loneliness, it also helped to improve their cognitive state, such as improving concentration. Furthermore, once the alone time was over, people's moods tended to increase significantly. Solitude is also associated with other positive growth experiences, religious experiences, and identity building such as solitary quests used in rites of passages for adolescents.
Loneliness can also play an important role in the creative process. In some people, temporary or prolonged loneliness can lead to notable artistic and creative expression, for example, as was the case with poet Emily Dickinson, and numerous musicians[who?]. This is not to imply that loneliness itself ensures this creativity, rather, it may have an influence on the subject matter of the artist and more likely be present in individuals engaged in creative activities.
The other important typology of loneliness focuses on the time perspective. In this respect, loneliness can be viewed as either transient or chronic. It has also been referred to as state and trait loneliness.
Transient (state) loneliness is temporary in nature, caused by something in the environment, and is easily relieved. Chronic (trait) loneliness is more permanent, caused by the person, and is not easily relieved. For example, when a person is sick and cannot socialize with friends would be a case of transient loneliness. Once the person got better it would be easy for them to alleviate their loneliness. A person who feels lonely regardless of if they are at a family gathering, with friends, or alone is experiencing chronic loneliness. It does not matter what goes on in the surrounding environment, the experience of loneliness is always there.
The existentialist school of thought views loneliness as the essence of being human. Each human being comes into the world alone, travels through life as a separate person, and ultimately dies alone. Coping with this, accepting it, and learning how to direct our own lives with some degree of grace and satisfaction is the human condition.
Some philosophers, such as Sartre, believe in an epistemic loneliness in which loneliness is a fundamental part of the human condition because of the paradox between people's consciousness desiring meaning in life and the isolation and nothingness of the universe. Conversely, other existentialist thinkers argue that human beings might be said to actively engage each other and the universe as they communicate and create, and loneliness is merely the feeling of being cut off from this process.
There are several estimates and indicators of loneliness. It has been estimated that approximately 60 million people in the United States, or 20% of the total population, feel lonely. Another study found that 12% of Americans have no one with whom to spend free time or to discuss important matters. Other research suggests that this rate has been increasing over time. The General Social Survey found that between 1985 and 2004, the number of people the average American discusses important matters with decreased from three to two. Additionally, the number of Americans with no one to discuss important matters with tripled (though this particular study may be flawed). In the UK research by Age UK shows half a million people more than 60 years old spend each day alone without social interaction and almost half a million more see and speak to no one for 5 or 6 days a week.
Loneliness appears to have intensified in every society in the world as modernization occurs. A certain amount of this loneliness appears to be related to greater migration, smaller household sizes, a larger degree of media consumption (all of which, it should be noted, have positive sides as well in the form of more opportunities, more choice in family size, and better access to information), all of which relates to social capital.
Within developed nations, loneliness has shown the largest increases among two groups: seniors and people living in low-density suburbs. Seniors living in suburban areas are particularly vulnerable, for as they lose the ability to drive, they often become "stranded" and find it difficult to maintain interpersonal relationships.
Americans seem to report more loneliness than any other country, though this finding may simply be an effect of greater research volume. A 2006 study in the American Sociological Review found that Americans on average had only two close friends in which to confide, which was down from an average of three in 1985. The percentage of people who noted having no such confidant rose from 10% to almost 25%, and an additional 19% said they had only a single confidant, often their spouse, thus raising the risk of serious loneliness if the relationship ended. The modern office environment has been demonstrated to give rise to loneliness. This can be especially prevalent in individuals prone to social isolation who can interpret the business focus of co-workers for a deliberate ignoring of needs.
Whether a correlation exists between Internet usage and loneliness is a subject of controversy, with some findings showing that Internet users are lonelier and others showing that lonely people who use the Internet to keep in touch with loved ones (especially seniors) report less loneliness, but that those trying to make friends online became lonelier. On the other hand, studies in 2002 and 2010 found that "Internet use was found to decrease loneliness and depression significantly, while perceived social support and self-esteem increased significantly" and that the Internet "has an enabling and empowering role in people's lives, by increasing their sense of freedom and control, which has a positive impact on well-being or happiness." The one apparently unequivocal finding of correlation is that long driving commutes correlate with dramatically higher reported feelings of loneliness (as well as other negative health impacts).
Loneliness has been linked with depression, and is thus a risk factor for suicide.Émile Durkheim has described loneliness, specifically the inability or unwillingness to live for others, i.e. for friendships or altruistic ideas, as the main reason for what he called egoistic suicide. In adults, loneliness is a major precipitant of depression and alcoholism. People who are socially isolated may report poor sleep quality, and thus have diminished restorative processes. Loneliness has also been linked with a Schizoid character type in which one may see the world differently and experience social alienation, described as the self in exile.
In children, a lack of social connections is directly linked to several forms of antisocial and self-destructive behavior, most notably hostile and delinquent behavior. In both children and adults, loneliness often has a negative impact on learning and memory. Its disruption of sleep patterns can have a significant impact on the ability to function in everyday life.
Chronic loneliness can be a serious, life-threatening health condition. It has been found to be associated with an increased risk of stroke and cardiovascular disease. Loneliness shows an increased incidence of high blood pressure, high cholesterol, and obesity.
Loneliness is shown to increase the concentration of cortisol levels in the body. Prolonged, high cortisol levels can cause anxiety, depression, digestive problems, heart disease, sleep problems, and weight gain.
?Loneliness has been associated with impaired cellular immunity as reflected in lower natural killer (NK) cell activity and higher antibody titers to the Epstein Barr Virus and human herpes viruses". Because of impaired cellular immunity, loneliness among young adults shows vaccines, like the flu vaccine, to be less effective. Data from studies on loneliness and HIV positive men suggests loneliness increases disease progression.
There are a number of potential physiological mechanisms linking loneliness to poor health outcomes. In 2005, results from the American Framingham Heart Study demonstrated that lonely men had raised levels of Interleukin 6 (IL-6), a blood chemical linked to heart disease. A 2006 study conducted by the Center for Cognitive and Social Neuroscience at the University of Chicago found loneliness can add thirty points to a blood pressure reading for adults over the age of fifty. Another finding, from a survey conducted by John Cacioppo from the University of Chicago, is that doctors report providing better medical care to patients who have a strong network of family and friends than they do to patients who are alone. Cacioppo states that loneliness impairs cognition and willpower, alters DNA transcription in immune cells, and leads over time to high blood pressure. Lonelier people are more likely to show evidence of viral reactivation than less lonely people. Lonelier people also have stronger inflammatory responses to acute stress compared with less lonely people; inflammation is a well known risk factor for age-related diseases.
When someone feels left out of a situation, they feel excluded and one possible side effect is for their body temperature to decrease. When people feel excluded blood vessels at the periphery of the body may narrow, preserving core body heat. This class protective mechanism is known as vasoconstriction.
There are many different ways used to treat loneliness, social isolation, and clinical depression. The first step that most doctors recommend to patients is therapy. Therapy is a common and effective way of treating loneliness and is often successful. Short term therapy, the most common form for lonely or depressed patients, typically occurs over a period of ten to twenty weeks. During therapy, emphasis is put on understanding the cause of the problem, reversing the negative thoughts, feelings, and attitudes resulting from the problem, and exploring ways to help the patient feel connected. Some doctors also recommend group therapy as a means to connect with other sufferers and establish a support system. Doctors also frequently prescribe anti-depressants to patients as a stand-alone treatment, or in conjunction with therapy. It may take several attempts before a suitable anti-depressant medication is found. Some patients may also develop a resistance to a certain type of medication and need to switch periodically.
Alternative approaches to treating depression are suggested by many doctors. These treatments include exercise, dieting, hypnosis, electro-shock therapy, acupuncture, and herbs, amongst others. Many patients find that participating in these activities fully or partially alleviates symptoms related to depression.
Another treatment for both loneliness and depression is pet therapy, or animal-assisted therapy, as it is more formally known. Studies and surveys, as well as anecdotal evidence provided by volunteer and community organizations, indicate that the presence of animal companions such as dogs, cats, rabbits, and guinea pigs can ease feelings of depression and loneliness among some sufferers. Beyond the companionship the animal itself provides there may also be increased opportunities for socializing with other pet owners. According to the Centers for Disease Control and Prevention there are a number of other health benefits associated with pet ownership, including lowered blood pressure and decreased levels of cholesterol and triglycerides.
A 1989 study found that the social aspect of religion had a significant negative association with loneliness among elderly people. The effect was more consistent than the effect of social relationships with family and friends, and the subjective concept of religiosity had no significant effect on loneliness.
One study compared the effectiveness of four interventions: improving social skills, enhancing social support, increasing opportunities for social interaction, addressing abnormal social cognition (faulty thoughts and patterns of thoughts). The results of the study indicated that all interventions were effective in reducing loneliness, possibly with the exception of social skill training. Results of the meta-analysis suggest that correcting maladaptive social cognition offers the best chance of reducing loneliness.
Klein was Clinical Director of the Masterson Institute and Assistant Professor of Psychiatry at the Columbia University College of Physicians and Surgeons, New York