Shyness is a behavior that is easily observable while being difficult to define. For instance, shyness may be viewed as a tendency to be self-conscious, uncomfortable, and anxious while socially engaged, especially upon an initial interaction [3,6]. Shyness has also been viewed as a cognitive dysfunction, in that a person feels responsible for social failures [5,7]. Because past research had difficulty operationally defining shyness, other terms were used, including "temperamentally or behaviorally inhibited" and "communication apprehension" [4,6].

Shyness is subjected to different theoretical orientations as well, and this has further complicated its definition. For example, Srivastava, John, Gosling, and Potter compared the Big Five factors (openness, conscientiousness, extraversion, agreeableness, and neuroticism) and the contextual theory of personality [8]. The former, also known as the plaster hypothesis, stated that personality was based upon biology and remained relatively stable throughout life [8]. The latter, by contrast, viewed personality as evolving through circumstance and subject to change based upon both critical life periods and the gender of the individual. Additional theoretical orientations included early attachment between child and caregiver and genetic and neurologic factors [2,3,7,9].

The tendency for social avoidance and affective states, such as anxiousness, have been studied in parental attachment theories and shyness, both indicators of early emotional adjustment and later social competency [5,6,11,12,13,14]. According to attachment theory, parents have influence over a child's personality development [15]. A secure bond results in a secure child who feels comfortable to explore the environment. The secure bond further allows the child to become accustomed to, and later involved in, interpersonal relationships. Overall, the literature was consistent in the finding that meeting a child's early emotional needs had long-lasting, positive social effects [7,9,11]. For instance, women showed both increased psychological well-being and social competence when securely attached to both figures as they transitioned into college [11].

According to this theory, it is probable that the maternal influence was traditionally stronger in the earlier years of development, as the mother likely spent more time with the child [15,16]. In a 2018 study, researchers found a link between marital conflict and parental attachment [14]. Specifically, higher marital conflict led to more negative emotions and fewer positive emotions when parents (particularly fathers) interacted with their children, with resultant impact on parent-child attachment [14]. These findings are consistent with the father-vulnerability hypothesis, which states that fathers' parenting is likely to be adversely affected by marital conflict [14]. Measured parent behaviors included the negotiation of marital problems and the amount of self-reported responsibility one assumed during conflict. Sensitive parental behaviors were defined as promptness and appropriateness of parent responses to the child. Finally, parenting attitude was defined by how much the parent enjoyed playing with the child as observed by positive interactions or the amount of physical and verbal activity with the child.

The findings of these studies have been replicated in many others, with marital conflict playing a role in attachment, an indicator of later social competency [5,6,11,12,13,14]. However, the degree to which a particular parent had a stronger influence was unclear, especially when factors such as genetics and cognitive self-talk were introduced [14,15,16]. To further complicate the role of attachment in the later development of shyness, studies also examined the role of race and perceived parental bond. For instance, Rice, Cunningham, Young, and Mitchell researched parental attachment, gender differences, and the influence of race in a sample of college students [16]. Assessments were utilized to rate the participants' perceived parental bond, social competencies, and overall emotional well-being. With the application of each measure, the authors hoped to expand upon attachment theory literature and measure the social competencies of both African American and White adolescents.

Based on published research, shyness appears to at least partially originate from the quality of the early attachment between child and caregiver. This cross-cultural phenomenon has been noted in both overall theory and empirically based studies [7,9,11,15,16]. An indirect influence on attachment is marital discord, the degree of which negatively impacts parent and child interactions [14]. The unfortunate outcome of insecurely attached children is lifelong social anxieties [19].

The first stage of psychosocial development, trust vs. mistrust, begins at birth, when infants rely upon their parent or caregiver to provide comfort. If comfort is provided, infants develop a sense of trust, which is both a first social milestone and an emerging confidence. Specifically, children develop confidence when the primary caregiver's routine and schedule is reliable. If trust or confidence does not develop, the psychological well-being may be negatively impacted. In one study, poor parental attachment was associated with an increase in feelings of defectiveness and risk of suicide in college students [11].

The next stage is initiative vs. guilt. Initiative is a natural progression from autonomy, as the child feels a sense of pride and develops confidence to engage in goal-seeking behaviors [20]. At this stage, the child begins to separate from the parent as he or she begins school. If he or she successfully resolves previous conflicts, primarily through parental encouragement and modeling, the ability to cooperate and learn from other adults develops. In addition, the child feels confident in his or her abilities to establish and reach goals.

In shyness, parenting research has primarily centered on parenting styles [13,18]. As noted, important factors that contribute to shyness include socialization and parental modeling [4]. Examining the role of perceived parenting in shyness is important, as factors such as low familial warmth, utilizing criticism and shame for discipline, feeling a lack of parental support, and overly controlling parents have been noted to intensify shyness [21,23,24].

Self-criticism is a primary characteristic of shyness, and studies have investigated the relationship between negative self-talk and perceived parenting [22]. In one study, participants with higher levels of self-criticism perceived parents as rejecting and restrictive, especially the same-sex parent [22]. Self-criticism and depressive symptoms during adolescence were related to the perception that parents (particularly mothers) are being psychologically controlling [22].

In another study, female college students were analyzed using the Social Reticence Scale (SRS), which focused on difficulties related to shyness, and the Children's Report of Parent Behavior Inventory, which examined perceived parental behaviors [18,25]. The results showed that less shy women perceived better relationships with their mothers. Any significant correlation involved the same-sex parent, and findings alluded to a maternal influence on shyness in college-aged women. Women deemed shy tended to perceive mothers as both unaccepting and anxious. The results indicated an insignificant relationship between father/daughter dyads, which was supported by additional research [22].

Attributional style is the manner by which one explains life experiences and can lean toward optimism or pessimism [5]. Attribution is comprised of three factors, each falling within a continuum: locus of control, stability, and controllability [27]. The first, locus of control, is determined by the extent to which a person assigns cause to an event to internal (positive) or external (negative) factors. In other words, cause is either attributed to the self or something in the environment. Stability is defined by whether the cause of an event is fixed (negative) or variable (positive); a person may believe the causal factor can change over time or that it is unchanging (e.g., luck or chance). The final factor is controllability, or the extent to which a person believes that capability for change (either internally or externally) is achievable [28]. Shyness is correlated with negative attribution styles, whereby the person perceives limited control. In shy individuals, causal attributions are perceived to be resistant to change, and as such, negative outcomes are expected [29].

Two shy people may respond differently to a given social situation, and it is believed that perceived control of this personality trait may be responsible [32]. A shy person may minimize his or her shyness based upon cognitive mediation, motivation, and self-awareness. This implicit theory of shyness is based on both entity theorists, who believe that personality is fixed, and incremental theorists, who believe that personality is dynamic. For example, a shy person would likely fail socially if he or she believed that shyness was unchangeable. Conversely, a person who felt that shyness was controllable could socially succeed.

A shy individual will often attribute perceived social failures to something within the self. Specifically, scenarios with positive outcomes were externally dismissed as luck or chance, while those with negative outcomes resulted in self-blame [29,30]. The magnitude of this belief was dependent upon how the individual perceived shyness; cognitive mediation in social situations is instrumental [32].

The authors concluded that parents of inhibited children tended to display higher levels of anxiety [4]. This parental anxiety was positively correlated with behavioral inhibition of the children in the study, suggesting a biologic influence to shyness. This anxiety was especially triggered in unfamiliar situations. As a consequence of anxiety, parents with inhibited children displayed decreased extroversion, increased social avoidance, and shyness. The authors related that the occurrence of shyness in children was based on a diathesis, whereby behavioral inhibition was both genetic and environmentally triggered. While parents are not seen as the sole cause of a child's shyness, they are believed to establish conditions in which shyness is possible [33].

In a physiologic study of personality, researchers examined brain reactivity to emotional stimuli and its impact on personality [2]. This study was based upon the Big Five factor personality traits, specifically extraversion and neuroticism. The study involved 68 participants (46 women and 22 men) who assessed the emotional states of muted video clips. The authors noted that the bilateral medial temporal gyrus (MTG) was identified as a key region in the processing of emotional faces and that this region correlated with neuroticism scores [2]. Female participants had much stronger activation differences between emotional and neutral facial expressions in the left MTG [2]. Further, the higher the neuroticism score, the stronger the action in the bilateral MTG for both genders [2]. In the right MTG, activation to positive stimuli was correlated with neuroticism. This neuroticism factor is considered especially important as it is linked to feelings of anxiousness and apprehension [2]. As a personality trait, neuroticism has been described as feeling lonely, even while in the presence of others, and feeling worried and tense without identifiable cause [34]. Other research has shown that those who score higher in measures of neuroticism may be more likely to react with fear, the emotion that maintains shyness [3]. Cognitively, the specific fears or worries that reinforce shyness are related to how a shy person believes he or she is perceived by others [35].

Physiologic and neurologic differences were noted in shy and non-shy preschool students in a study of how each population processed emotion [3]. Theall-Honey and Schmidt hypothesized that shy children would display significantly greater brain activity in the right anterior portion of the brain (as indicated by an EEG) when watching emotionally stimulating movie clips [3]. In addition, the authors predicted the baseline heart rate of shy children would be higher when compared to non-shy peers. Overall, they found that shy children displayed significantly stronger EEG activity in the right central part of the brain while at rest when compared with non-shy children [3]. The authors concluded that shy children showed the strongest EEG responses with clips that elicited fear. This finding is important, as fear is the emotion that maintains shyness. Furthermore, shy girls displayed a pattern of significantly higher right frontal EEG activity both without emotional stimulation and in response to clips that evoked fear and sadness when compared with shy boys. Shy children perceived the video clips with negative emotions more intensely when compared to the non-shy children. Finally, all children assessed as shy showed an overall higher baseline heart rate without stimulation than non-shy children.

Research consistently indicates that existing gender differences impact degree of shyness [35,36]. Gender-specific consequences have been noted as a result of these differences [31,37]. The resulting behaviors range from delayed romantic involvement and physical aggression in boys and men, to difficulty concentrating as a result of socially triggered anxiety in girls and women [36,38].

Research has indicated that shy boys are more prone to depression as they transition from the end of high school to the end of the first semester at college than girls [37]. This is generally due to their difficulty adjusting to the demands of college and being more preoccupied with their parents compared to girls. Furthermore, as discussed, physiologic differences have been identified between male and female preschoolers, specifically in brain reactivity to unpleasant emotions [3].

Male shyness has been linked to consequences of varying severity, including difficulty initiating romantic relationships [31]. It is important to acknowledge and study shyness in men despite a potential unwillingness due to the vulnerability of previously discouraged self-disclosure. More critically, research has indicated a type of cynical shyness in men. In cynical shyness, men displayed a strong desire for social involvement but lacked social skills and, consequently, were repeatedly rejected by peers. As rejection re-occurred, the unexpressed emotional pain intensified, resulting in anger and hatred. Men with cynical shyness who lacked coping skills and/or resilience have been found to be more likely to commit acts of violence [38].

As noted, although similar in some respects, shyness is considered a personality trait, while social anxiety disorders are impairing psychiatric disorders. However, due to limited research dedicated to shyness, many of the treatment approaches for shyness are modeled from those used for social anxiety disorders [43,44]. The most common approaches include cognitive-behavioral therapy, systematic desensitization, and skills training, including assertiveness training and positive affirmations. The Stanford/Palo Alto Shyness Clinic has identified seven approaches to treating shyness, which may be applied to each individual in various combinations [44]: