Friendship is a form of interpersonal relationship generally considered to be closer than association, although there is a range of degrees of intimacy in both friendships and associations. Friendship and association are often thought of as spanning across the same continuum. The study of friendship is included in the fields of sociology, social psychology, anthropology, philosophy, and zoology. Various academic theories of friendship have been proposed, among which are social exchange theory, equity theory, relational dialectics, and attachment styles.
In the sequence of the emotional development of the individual, friendships come after parental bonding and before the pair bonding engaged in at the approach of maturity. In the intervening period between the end of early childhood and the onset of full adulthood, friendships are often the most important relationships in the emotional life of the adolescent, and are often more intense than relationships later in life. However, making friends seems to trouble a lot of people; having no friends can be emotionally damaging in some cases.
The conventional wisdom is that good friendships enhance an individual's sense of happiness and overall well-being. But a number of solid studies support the notion that strong social supports improve a woman's prospects for good health and longevity. Conversely, it has been shown that loneliness and lack of social supports are linked to an increased risk of heart disease, viral infections, and cancer as well as higher mortality rates. Two female researchers have even termed friendship networks a "behavioral vaccine" that protects both physical and mental health.