Genes influence various adolescent sexual behaviors including sexual abstinence, sexual initiation, and number of sexual partners. These influences also appear to be more significant for males (Mustanski, Viken, Kaprio, Winter, & Rose, 2007). For instance, Verweij and colleagues (2009) examined current risky sexual behaviors in adults and retrospective misconduct during adolescence and discovered that genetics accounted for approximately one-third of the variance in understanding risky sexual behaviors among late adolescent and adult twins. In addition, gender trends were observed such that shared environmental factors seemed to be more significant in the relationship between adolescent misconduct and risky sexual behaviors for females, while genetic influences were more significant for males (Verweij, Zietsch, Bailey, & Martin, 2009). In another study, researchers discovered a much closer relationship in the timing of sex among identical twins as compared to fraternal twins. For example, the probability of first sex was approximately 30 % greater when an identical twin had initiated sex as compared to the twin being a virgin. This relationship was not observed among same-sex fraternal twins. Also, Asian American, European American, and Hispanic American adolescents who possessed a 3R allele of the dopamine receptor DRD4 gene were significantly more likely to have engaged in first sex. This relationship was not found among African American adolescents (Guo & Tong, 2006).

Gender nonconformity also seems to have a heritable quality for both males and females (Bailey, Dunne, & Martin, 2000). In fact, genes have been implicated in gender atypical behavior during childhood and later sexual orientation. Again, the relationship between genes and behavior appears stronger for males (Alanko et al., 2010). Significant skewing of X-chromosome inactivation has also been associated in mothers with gay sons. This relationship appears to be stronger among mothers with more than one son who identifies as homosexual (Bocklandt, Horvath, Vilain, & Hamer, 2006). Similarly, having more female relatives, such as aunts, is more prevalent in female-to-male transsexuals. This relationship has not yet been established in male-to-female transsexuals (Green & Keverne, 2000).

These studies suggest that genes are involved in adolescent sexual behaviors with early displays of genetic influences observed in gender atypical behavior during childhood. Variations in genetic influences have been observed among different ethnic groups and among males. Moreover, genes appear to be implicated in the development of sexual orientation to some degree. All the same, it is likely that a combination of genetic and non-shared environmental factors influence adolescent sexual behaviors.

Variation in adolescent development of sexual identity and sexual behaviors has been consistently highlighted within research investigating congenital adrenal hyperplasia (CAH). In fact, substantial understanding of the influence of congenital hormone anomalies on gender identity, sexual orientation, and sexual interest has emerged during the past 30 years. In attempting to understand variation in adolescent development of sexual identity and sexual behaviors, examining research of CAH is particularly illustrative. CAH occurs as a result of a variety of intra-uterine sex hormone exposure, via fetal or maternal sources. Specifically, key enzymes involved in the synthesis of adrenal glucocorticoid hormones become mutated. These mutations render the enzyme partially or completely ineffective, leading to an excess of hormone intermediaries. These intermediaries may have potent effects on expressions of sexuality during adolescence or on genitals themselves (girls with CAH are born with an XX chromosome pattern but may be substantially virilized). The majority of women with CAH report different-sex (i.e., heterosexual) sexual orientation, although women with CAH are much more likely than unaffected women to express same-sex fantasies and behaviors (Cohen-Bendahan, van de Beek, & Berenbaum, 2005). Some studies show that young women with CAH do not differ from other women in terms of age at menarche, age of initiation of masturbation, age at first partnered sex, and age of first orgasm (Meyer-Bahlburg, Dolezal, Baker, & New, 2008). However, other studies suggest that women with CAH may be delayed in terms of onset of partnered sexual activity (Dittmann, Kappes, & Kappes, 1992).

Another illustration of potential antenatal influences on sexual orientation relates to the ratio of the lengths of the second and fourth fingers (2D:4D). Males typically develop a smaller 2D:4D ratio, presumably as an effect of intrauterine androgen exposure (Rahman & Wilson, 2003). This gender dimorphism becomes especially apparent during puberty (Friedman & Downey, 2008). A substantial body of research has addressed 2D:4D ratio as a marker for sexual orientation. A recent meta-analysis of these studies confirmed the markedly lower 2D:4D ratio in males with different-sex orientation compared to females with different-sex orientation. Women with same-sex orientation have smaller (i.e., more masculine) 2D:4D ratios compared to women with different-sex orientations. However, no differences were noted in men with same- and different-sex orientations (Grimbos, Dawood, Burriss, Zucker, & Puts, 2010).

Overall, understanding potential antenatal influences on other characteristics of adolescent sexuality and sexual behavior, such as age at first coitus or preferred number of sexual partners, remains quite meager. Data are emerging to provide a more detailed understanding of antenatal hormonal effects on characteristics such as sexual orientation, but some of these data remain controversial. Additionally, very few studies have gathered prospective data from adolescents themselves. Thus, we still know little about the developmental experience of sexuality and sexual behaviors of various potential antenatal exposures as they unfold during adolescence.

Gender differences in sexuality are often noticeable early in development and include behaviors such as preferences for sex-typed toys among boys and girls (Hassett, Siebert, & Wallen, 2008). It has been argued that these types of preferences occur at their earliest stages because young girls are programmed to seek objects that imply nurturance, while young boys are interested in objects that suggest movement or excitement (Alexander & Hines, 2002). However, these differences are also likely to occur within an environment that reinforces or punishes such behaviors. From early age, young boys and girls are treated differently by parents and peers for engaging in play behaviors that are deemed appropriate for their gender. Fathers tend to display more positive reactions to daughters and provide more negative feedback to boys playing with cross-gendered toys. On the other hand, mothers and peers exhibit more rewards for play with gendered toys and mothers tend to be more positive overall about their children’s play (Langlois & Downs, 1980). Play preferences are a significant part of sexuality development, as it has been linked with later homosexual orientation (Alanko et al., 2010). Even when play behavior decreases, other gender differences still persist throughout adolescence.

In a study of middle and late adolescent women, researchers examined two qualities, relationship authenticity and body objectification, associated with feminist ideology. They discovered that young women who were less authentic in friendships and those who felt more negative about their body demonstrated less sexual self-efficacy or feelings of being in sexual control within their sexual relationship. Lower sexual self-efficacy was also predictive of less hormonal contraceptive use and greater use of condoms during first sex. Similarly, negative feelings about one’s body were related to lower rates of condom use. The authors argued that being less authentic and feeling less positive about one’s body may be associated with traditional feminine ideology and less perceived sexual control. Ironically, young women also tended to view aggression as a desirable quality in a potential partner (Impett, Schooler, & Tolman, 2006). This relationship might be due to the association that young men who display aggressive qualities may appear older or more distinctive (Bukowski, Sippola, & Newcomb, 2000).

Pleck and others (1993) examined the masculine ideology of middle and late adolescent men and discovered that young men who held more traditional views of romantic relationships viewed heterosexual relationships as more oppositional, believed that it was their partner’s responsibility to prevent pregnancy, believed that getting a relationship partner pregnant is a vital part to being a man, endorsed more overall sexual partners, demonstrated a negative view of condoms, and used condoms less regularly (Pleck, Sonenstein, & Ku, 1993). In a more recent study, Giordano and colleagues (2006) found disparate results which indicated that young men expressed greater feelings of awkwardness when communicating with a dating partner. Young men were also less confident within romantic relationships, although young men who engaged in sexual activity with their romantic partner felt more confident within their relationship. Participants also endorsed greater levels of attempted interpersonal influence and this influence increased throughout the length of the relationship. However, young men were less likely to view themselves positively with regard to having power within their relationship, as they endorsed actual influence deriving from their relationship partner (Giordano, Longmore, & Manning, 2006).

In a retrospective account of gender differences within partnered relationships, Morgan and Zurbriggen (2007) found that sexual gender roles are very prevalent among adolescents engaging in sexual intercourse. When recounting their first sexual experience during adolescence, adult women reported feeling pressured to engage in sex. Adult women also had beliefs that their male sexual partner ascribed to masculine values. Adult men recounted that their first female sexual partner wanted to set sexual boundaries. However, both men and women highlighted the significance of sexual negotiations within their first sexual encounter. This suggests that sexual negotiating is an important part of developing one’s sexual identity and communicating within an adolescent sexual relationship.

Gender influences likely occur through a system of reinforcement and punishment from parents, family members, and peers. Adolescents appear to ascribe to specific gendered roles which are quite different for young men and young women. Young women in particular tend to report feeling pressured to engage in sex. Nonetheless, our understanding of these experiences appears to be more complex then early research in this area has suggested. That is, young men may be more aware of and in touch with the emotional component of sexuality than previous research has asserted. Young women may also be making partnering decisions with the intent of locating a more distinctive, aggressive partner, but may, in actuality, be increasing their probability of lowered sexual self-efficacy. Overall, adolescent pathways of gender development may be more similar than divergent for young men and young women. It is probable that both young men and young women have similar sexuality experiences, but they may experience very different reinforcement strategies from parents and peers. Accordingly, they may encounter a host of punishing behaviors if they do not display their sexual emotions and behaviors in a gendered-specific manner.

Throughout childhood, parents play an increasing role in their children’s lives. From managing their basic survival necessities, they also present morals, values, and messages regarding acceptable and appropriate sexual behavior. Parents who engage in open and responsive communication, tend to have adolescents with intentions to delay sexual activity for at least 1 year (Fasula & Miller, 2006). Whitaker and Miller (2000) also discovered that adolescents who had discussion with their parents about sex tended to initiate sex later and have fewer sexual partners. Additionally, parents who discussed condom use were more likely to have adolescents who had ever used condoms, had used condoms at their most recent sexual event, and who used condoms more consistently overall. Moreover, they found that adolescents who communicated with their parents about sex and condom use were less influenced by peers and more likely to report that their parents provided more accurate information about sex as compared to adolescents who had not engaged in such conversations.

Another way that parents have been shown to be a significant influence on adolescent sexual behavior is through parental monitoring. Adolescents with lower levels of parental monitoring tend to engage in sexual intercourse at a younger age. This relationship is especially significant among young women who have more sexual partners and are less likely to use any form of contraceptives during sex intercourse (Wight, Williamson, & Henderson, 2006). Researchers have also found that parental monitoring techniques and its effects vary across ethnic groups. For example, Pearson and colleagues (2006) examined the specific aspects of parental involvement that influence initiation of sexual activity among European American, African American, and Latino American adolescents. Results from this study indicated that adolescents living with two biological parents were less likely to engage in sexual behaviors as compared to adolescents with other family formations. However, African American adolescents residing with step-parents were no more likely than those residing with biological parents to initiate sex. In addition, shared dinnertime, parent-adolescent communication about sex, shared parent-adolescent activities, and having a close parent-adolescent relationship was related to European American adolescents being less likely to ever initiating sex. However, with regard to sexual initiation, engaging in shared activities was the only significant parent-adolescent factor for African American adolescents and communicating about sex was the only significant parental monitoring technique among Latino American adolescents (Pearson, Muller, & Frisco, 2006). Although it is likely that other parental factors do in fact influence feelings of social support and sexual behaviors among African American and Latino American adolescents, it is possible that cultural differences within parent–adolescent relationships may not have been captured by the instruments utilized in this study.

Taken together, parents play a vital role in the engagement of their adolescent’s sexual behaviors. Both parental communication and parental monitoring have significant influences on not only adolescent beliefs but also the behaviors with which they engage. These techniques appear to delay intent to engage in sexual intercourse, an increase in parental status regarding sexual information, and reduced sexual risk-taking through increased condom use and fewer sexual partners. Parents are strongly encouraged develop an open dialogue with their adolescents about sexuality, sexual behaviors, contraceptive use and parental values of preferred adolescent behavior. Preferably, these conversations would occur during preadolescence. This would promote an open dialogue for adolescents to seek out additional information from their parents, clarify inconsistencies in sexual knowledge, and problem-solve sexual conflicts.

Similar to parents, siblings also provide a significant model with regard to sexual behavior. These effects tend to be more influential when siblings are older and more alike. For example, adolescents with older siblings are more likely to have engaged in sexual behaviors. This effect appears to be most significant for adolescent with siblings who are 4 or more years older than themselves. In addition, research demonstrates a subthreshold trend that young women with an older sibling tend to be less likely to use contraception during their first sexual intercourse encounter (Argys, Rees, Averett, & Witoonchart, 2006).

Having a good relationship with a sibling or having a sibling who is more genetically similar has also been linked to risky sexual behaviors. Also, stronger attitudes about becoming pregnant have also been associated among siblings who are more biologically similar (McHale, Bissell, & Kim, 2009). For instance, young women who report higher levels of companionship with their older sister are more likely to become pregnant. Likewise, young women have a greater probability of becoming pregnant if their older sister has experienced a pregnancy or if both their older sister and mother have experienced a teenage pregnancy. However, when teenage pregnancies of mothers and older siblings are compared, young women have a greater chance of becoming pregnant if their older sister experienced a pregnancy as compared to their mother having experienced a pregnancy when she was a teenager (East, Reyes, & Horn, 2007).

Overall, having an older sexually active sibling shapes adolescent sexuality and sexual behaviors. Adolescents with older siblings have the opportunity to learn from their sibling’s experience, be more encouraged to participate in sexual activity, or be less inclined to follow in their sibling’s footsteps. These relationships appear to be stronger when adolescents are more biologically similar to their siblings or share a closer relationship to their sibling. However, much of the research conducted to date has investigated sibling relationships among young women. Although it is likely that older male siblings also influence sexual behaviors among young men, additional research is needed to examine these relationships.

The impact of peers on adolescent sexual behaviors is notable, complex, and strengthens across time. Not surprisingly, peers often set norms for sexual behaviors (Kinsman, Romer, Furstenberg, & Schwarz, 1998) and these norms are likely established both overtly (e.g., increased social status) or subtly (e.g., encouraging the perception of participation in sexual behaviors). Although the differences in sexual behavior as a result of either norm has yet to be clearly established, perception of peer engagement of sexual activity has been associated with having more sexually experienced friends, perceiving more respect from friends, being more involved with friends (Sieving, Eisenberg, Pettingell, & Skay, 2006), and initiating sexual activity (Zimmer-Gembeck & Helfand, 2008). The literature has also highlighted that adolescents who are not themselves engaging in sexual behaviors may feel hindered by their limited ability to contribute to conversations with peers (Skinner, Smith, Fenwick, Fyfe, & Hendriks, 2008). This suggests that adolescents may perceive the peer norm to participate in discussions about sexual behaviors through sharing relevant and personal experience.

Peer influences also vary across sexual behaviors. One such example is that peers influence oral sex behaviors more readily than vaginal intercourse behaviors. Prinstein and colleagues (2003) found a relationship between the reported numbers of oral sex partners among adolescents and their perceived number of oral sex partners for their best friends. Adolescents who endorsed engaging in more oral sex were considered to be more popular but less friendly. The researchers also found that peers shape sexual intercourse behaviors, especially if adolescents perceive that their peers engaged in sexual intercourse at a younger age, were currently engaging in sexual intercourse, or that social status would be gained as a result of sexual intercourse (Prinstein, Meade, & Cohen, 2003). Ironically, in the same way that peer influence may be negative through increased pressure to initiate sexual activity, peer pressure may also be protective with regard to contraceptive use. In another study, it was found that having the belief that peers are more likely to use condoms during sexual activity was linked to a greater desire to use condoms at first sex and an increased use of some form of contraception during sexual intercourse, especially among young men (Potard, Courtois, & Rusch, 2008).

Some have even suggested that the media may represent a “super peer” by influencing early adolescents’ interest in advanced sexual behaviors (Brown, Halpern, & L’Engle, 2005). This hypothesis was demonstrated by a study that investigated adolescent sexual behavior and the media domain of music, adolescents who listened to greater amounts of sexually degrading music lyrics were more likely to engage in sexual intercourse and other sexual behaviors (i.e., masturbation). Notably, music with strong sexual themes without degrading lyrics was not related to adolescent sexual behaviors (Martino et al., 2006). This implies that sexual themes alone do not promote sexual behavior. Rather, the addition of degrading lyrics appears to be the key feature in encouraging adolescents to participate in sexual behavior. Another media study examined the relationship between sexual content from four media domains (i.e., television, movies, music, and magazines) among African American and European American adolescents across time. Researchers discovered that adolescents aged 12–14 with the highest media exposure to sexual content were more likely to have engaged in sexual intercourse 2 years later. However, this trend was more widely observed among European American adolescents (Brown et al., 2006). It is possible that the association between the media was not as prevalent for African American adolescents because much of the content within these domains did not reflect basic demographic characteristics of these adolescents (i.e., skin color). Thus, the likely reduced salience across media domains may have led to reduced media comparisons, resulting in less media influence among African American adolescents.

By and large, peers have a substantive influence on perception of sexual activity, contraception, and various sexual behaviors. The influence of peers may be more subtle, such as making adolescents feel bad if they cannot contribute to a conversation about sexual activity or more overt such as improved social status through engaging in various sexual behaviors. Paradoxically, the media which is operated and controlled by adults also functions as a peer by providing explicit cues about appropriate sexual activity, although the influence of these effects may be more relevant across groups of adolescents. Nevertheless, peers influence is most apparent among adolescents who lack adequate communication with their parents about sexual behaviors and using condoms (Whitaker & Miller, 2000).

As the common saying goes, “it takes two to tango,” most sexual behaviors involve a sexual partner. Sexual partnerships often play an increasing role as individuals shift from middle to late adolescence and early adulthood. These relationships encompass a wide variety of dynamics including age of first partnership, age differentials between partners, emotional connectedness, sexual power, sexual gender roles, and sexual negotiation. While many of these variables may be involved in adolescent sexual relationships to some degree, the literature is clear that the outcomes of these variables may differ among young men and young women.

In a longitudinal study investigating relationship experiences between adolescent men and women, researchers discovered interesting gender similarities and differences. Both young men and young women who participated in a relationship in the seventh grade demonstrated a greater probability of being sexual active by the ninth grade. However, young women who had older boyfriends in the seventh grade were even more likely to have engaged in sexual activity in ninth grade. This relationship was not found among young men. In addition, when young women were compared to each other, those who experienced menarche in sixth grade were more likely to be in relationships with young men who were at least 2 years older than themselves (Marín, Kirby, Hudes, Coyle, & Gómez, 2006). Another study found that approximately one-third of adolescents engage in sexual partnerships with older individuals. Characteristics associated with these adolescents include having an older peer group, attending a school with a wider grade span, being younger, using substances, endorsing higher levels of communication with their parents, having less educated parents, or being foreign born (Manlove, Ryan, & Franzetta, 2007).

Other partner characteristics such as feeling emotionally close to a romantic partner or perceiving that a romantic partner has more power has been demonstrated to influence adolescent sexual behaviors. For example, when adolescent participants were asked who they perceived to have more power within romantic relationships, both young men and young women agreed that they perceived young women to have more power within romantic relationships. However, young men were found to have more actual power in adolescent relationships (Giordano, Manning, & Longmore, 2010). Power differentials are important as risky sexual behaviors have been observed among adolescents who want to please their partner because they perceive their partner as having more relationship control (Marston & King, 2006). For instance, young women have reported that despite not feeling ready to initiate sexual intercourse, they have done so out of fear of losing a relationship partner or due to concern that their relationship partner may feel unsatisfied (Skinner et al., 2008). Moreover, Blythe and colleagues (2006) found that within a 3-month span, approximately 40 % of young adolescent women reported experiencing unwanted sexual intercourse at least once and over one-third of young women reported engaging in unwanted sexual intercourse out of concern that their partner would become angry if they refused (Blythe, Fortenberry, Temkit, Tu, & Orr, 2006).

These studies reveal that sexual partners play a very significant role in influencing adolescent sexual behaviors. Early experiences with a romantic partner are related to the increased probability that adolescent young women will become sexual active. In addition, perception of relationship power and actual relationship power has been demonstrated to be important components of adolescent relationships. This may be especially relevant among young women who may feel pressured to engage in unwanted sexual behaviors because they perceive that their sexual partners have more relationship power or that their partner may become angry and/or decide to leave the relationship. Also, young women who participate in romantic partnerships with older young men may experience an even greater power dynamics within their relationship. Of note, a lack of parental involvement and monitoring was implicated as a risk factor for young women participating in relationships with older partners. This again highlights the role that parents play in mitigating the effects of undesirable partner influences. Moreover, additional partner research that is squarely focused on young men would be valuable to better understanding this area.

Social environments have also been shown to influence adolescent sexuality and sexual behaviors. Previous research has demonstrated distinct differences in the sexual behaviors of adolescents who reside in communities that are poor, structurally disadvantaged, lack supervision, experience greater incidents of crime, and/or have fewer available community resources (Cubbin, Santelli, Brindis, & Braveman, 2005; DiClemente et al., 2008; Sampson, Morenoff, & Gannon-Rowley, 2002). Accordingly, it is no surprise that adolescents who spend more time at home alone are more likely to engage in sexual behaviors (Buhi & Goodson, 2007).

Neighborhood influences on sexual behaviors have also been observed in a study by Browning and colleagues (2008). The investigators examined how immigrant populations, neighborhood level covariates and collective efficacy or the combined effects of parental and adult supervision of adolescents within one’s neighborhood predicted adolescents engaging in multiple sexual partnerships across time. Using data derived from the Project on Human Development in Chicago Neighborhoods and 1990 Census data, the researchers discovered that adolescents were more likely to report ever having a sexual partner if they were older, male, in the latter stages of puberty, living in concentrate poverty and/or if they had ever experienced past problem behaviors. Adolescents who reported higher levels of parental attachment and those who were first or second generation immigrants and lived in neighborhoods with low levels of immigrant populations were less likely to ever report having a sexual partner. Having ever had more than one sexual partner was related to being older, male and African American. Adolescents who endorsed greater collective efficacy were less likely to have ever experienced more than one sexual partner (Browning, Burrington, Leventhal, & Brooks-Gunn, 2008).

Perhaps one of the most frequently considered cultural aspects of adolescent sexuality and sexual behavior is religiosity. Religiosity has been associated with reduced risk-taking behaviors such as delinquency (Armour & Haynie, 2007) and delay of initiation of first sex among early, middle, and late adolescents (Zimmer-Gembeck & Helfand, 2008). In a recent study, adolescent young women who were affiliated with a religious organization during childhood were less likely to have ever engaged in oral sex or vaginal sex. Also, young men who consistently endorsed attending religious services during their childhood were more likely to be virgins and never have engaged in oral sex (Brewster & Tillman, 2008).

Norms and limits established within one’s culture and neighborhood likely serves as an example of appropriate adolescent sexual behavior. This is possibly why significant differences in sexual behaviors have been observed among adolescents residing in disadvantaged communities. Adolescents in these communities may have reduced opportunities and less parental monitoring experiences, thus increasing the influence of peers, relationship partners or perhaps other individuals in their community. Similarly, religiosity also models acceptable sexual behaviors as adolescents who ascribe to a particular religion delay initiating in sexual behaviors. These studies emphasize that adolescent sexual behaviors cannot be viewed in isolation. That is, consideration must be given to the context of one’s environment and relevant cultural factors.

Adolescents engage in a variety of sexual behaviors, with vaginal sex representing one of many forms of sexual expression. Accordingly, the variety and prevalence of sexual behaviors with which adolescents engage is central to understanding adolescent sexuality. For example, masturbation is a very common form of sexual expression throughout one’s life course. In studies of older adolescents and adults, masturbation is nearly universal among men and reported by a majority of women (Gerressu, Mercer, Graham, Wellings, & Johnson, 2008; Kinsey, Pomery, & Martin, 1948; Kinsey, Pomeroy, Martin, & Gebhard, 1953; Laumann, Gagnon, Michael, & Michaels, 2000; Pinkerton, Bogart, Cecil, & Abramson, 2003). In a recent national sample of sexual behaviors in the USA (see Table 1), masturbation was more common than any partnered sexual behavior among 14–17-year-old adolescents (Herbenick et al., 2010). In addition, masturbation onset has been shown to occur by early adolescence (between the ages of 11 and 13) in 53 % of males and 25 % of females (Janus & Janus, 1993).