In humans, shyness (also called diffidence) is a social psychology term used to describe the feeling of apprehension, lack of confidence, or awkwardness experienced when a person is in proximity to, approaching, or being approached by other people, especially in new situations or with unfamiliar people. Shyness may come from personality introversion, genetic traits, or the environment in which a person is raised.
In biology, shy generally means "tends to avoid human beings"; See crypsis. Shyness in gorillas manifests with ostensibly similar behavioral traits, but differs wholly from humans in cognition and motivation.
Shyness is most likely to occur during unfamiliar situations, though in severe cases it may hinder an individual in his or her most familiar situations and relationships as well. Admitting feelings may become difficult for the individual. Shy persons avoid the objects of their apprehension in order to keep from feeling uncomfortable and inept; thus, the situations remain unfamiliar and the shyness perpetuates itself. Shyness may fade with time; e.g., a child who is shy towards strangers may eventually lose this trait when older and more socially adept. This often occurs by adolescence or young adulthood (generally around the age of 13). In some cases, though, it may become an integrated, life-long character trait. Humans experience shyness to different degrees and in different areas. For example, an actor may be loud and bold on stage, but shy in an interview. In addition, shyness may manifest when one is in the company of certain people and completely disappear when with others— one may be outgoing with friends and family, but experience love-shyness toward potential partners, even if strangers are generally not an obstacle.
The condition of true shyness may simply involve the discomfort of difficulty in knowing what to say in social situations, or may include crippling physical manifestations of uneasiness. Shyness usually involves a combination of both symptoms, and may be quite devastating for the sufferer, in many cases leading them to feel that they are boring, or exhibit bizarre behavior in an attempt to create interest, alienating them further. Behavioral traits in social situations such as smiling, easily producing suitable conversational topics, assuming a relaxed posture and making good eye contact, which come spontaneously for the average person, may not be second nature for a shy person. Such people might only effect such traits by great difficulty, or they may even be impossible to display. Shyness is considered to be a neutral personality trait by people who are not shy, but a very negative trait by those who are shy themselves. In fact, those who are shy are actually perceived more negatively because of the way they act towards others. Shy individuals are often distant during conversation, which may cause others to create poor impressions of them, simply adding to their shyness in social situations.
The term shyness may be implemented as a lay blanket-term for a family of related and partially overlapping afflictions, including timidity (apprehension in meeting new people), bashfulness and diffidence (lack of assertiveness), apprehension and anticipation (general fear of potential interaction), or intimidation (relating to the object of fear rather than one's low confidence). Apparent shyness, as perceived by others, may simply be the manifestation of reservation or introversion, character traits which cause an individual to voluntarily avoid excessive social contact or be terse in communication, but are not motivated or accompanied by discomfort, apprehension, or lack of confidence.
Rather, according to Bernardo J. Carducci, director of the Shyness Research Institute, introverts choose to avoid social situations because they derive no reward from them, or may find surplus sensory input overwhelming. Conversely, shy people may fear such situations and feel that they "should" avoid them.  Shy people tend to perceive their own shyness as a negative trait, and many people are uneasy with shyness in others, especially in cultures which value individuality and taking charge. This generally poor reception of shyness may be misinterpreted by the suffering individual as aversion related to his or her personality, rather than simply to his or her shyness. Both conditions can lead to a compounding of a shy individual's low self-confidence.
In cultures that value outspokenness and overt confidence, shyness can be perceived as weakness. To an unsympathetic observer, a shy individual may be mistaken as cold, distant, arrogant or aloof, which can be frustrating for the shy individual. However in other cultures, shy people may be perceived as being thoughtful, intelligent, as being good listeners, and as being more likely to think before they speak. Furthermore, boldness, the opposite of shyness, may cause its own problems, such as impertinence or inappropriate behavior.
The initial causes of shyness vary. Scientists have located some genetic data that supports the hypothesis that shyness is at least partially genetic. However, there is also evidence that the environment in which a person is raised can affect their shyness. This includes child abuse, particularly emotional abuse such as ridicule. Shyness can originate after a person has experienced a physical anxiety reaction; at other times, shyness seems to develop first and then later causes physical symptoms of anxiety. Shyness differs from social anxiety, which is a broader, often depression-related psychological condition including the experience of fear, apprehension or worrying about being evaluated by others in social situations to the extent of inducing panic.
The genetics of shyness is a relatively small area of research that has been receiving an even smaller amount of attention, although papers on the biological bases of shyness date back to 1988. Some research has indicated that shyness and aggression are related—through long and short forms of the gene DRD4, though considerably more research on this is needed. Further, it has been suggested that shyness and social phobia (the distinction between the two is becoming ever more blurred) are related to obsessive-compulsive disorder. As with other studies of behavioral genetics, the study of shyness is complicated by the number of genes involved in, and the confusion in defining, the phenotype. Naming the phenotype – and translation of terms between genetics and psychology — also causes problems. In some research, "behavioral inhibition" is studied, in others anxiety or social inhibition is. One solution to this problem is to study the genetics of underlying traits, such as "anxious temperament."
Several genetic links to shyness are current areas of research. One is the serotonin transporter promoter region polymorphism (5-HTTLPR), the long form of which has been shown to be modestly correlated with shyness in grade school children. Previous studies had shown a connection between this form of the gene and both obsessive-compulsive disorder and autism. Mouse models have also been used, to derive genes suitable for further study in humans; one such gene, the glutamic acid decarboxylase gene (which encodes an enzyme that functions in GABA synthesis), has so far been shown to have some association with behavioral inhibition.
Another gene, the dopamine D4 receptor gene (DRD4) exon III polymorphism, had been the subject of studies in both shyness and aggression, and is currently the subject of studies on the "novelty seeking" trait. A 1996 study of anxiety-related traits (shyness being one of these) remarked that, "Although twin studies have indicated that individual variation in measures of anxiety-related personality traits is 40-60% heritable, none of the relevant genes has yet been identified," and that "10 to 15 genes might be predicted to be involved" in the anxiety trait. Progress has been made since then, especially in identifying other potential genes involved in personality traits, but there has been little progress made towards confirming these relationships. The long version of the 5-HTT gene-linked polymorphic region (5-HTTLPR) is now postulated to be correlated with shyness, but in the 1996 study, the short version was shown to be related to anxiety-based traits. This confusion and contradiction does not oppose the genetic basis of personality traits, but does emphasize the amount of research there is still to be done before the bases of even one or two of these characteristics can be identified.
Excessive shyness, embarrassment, self consciousness and timidity, social-phobia and lack of self-confidence are also components of erethism, which is a symptom complex that appears in cases of mercury poisoning. Mercury poisoning was common among hat makers in England in the 1700s and 1800s, who used mercury to stabilize wool into felt fabric.
Shyness as a psychiatric illness made its debut as "social phobia" in DSM-III in 1980, but was then described as rare. By 1994, however, when DSM-IV was published, it had become "social anxiety disorder" and was now said to be extremely common. This process has been adverted to as a case study of "disease-mongering" in psychiatry. One drug company product manager has been quoted as saying, "Every marketer's dream is to find an unidentified or unknown market and develop it. That's what we were able to do with social anxiety disorder".