Initial online searches yielded over 7020 hits. After removing duplicates and assessing eligibility, 37 studies were found that matched the inclusion criteria of this review. Included studies were published between January 1, 1990 and May 28, 2017.

Table 1 lists all 37 studies. The first studies were conducted in the 1990s (five studies), but the majority was conducted after 2000 (32 studies). Two pairs of studies were based on the same sample (Choudhry 2015; Choudhry et al. 2014; Fredlund et al. 2013; Svensson et al. 2013) and three studies comprised findings from separate waves in a prospective design (Lee and Shek 2013, 2014; Lee et al. 2016). Thus, the total number of unique studies was 33. Combined, all unique studies that reported sample size data (27 out of 33) had a sample size of 120,447 participants. The sample size ranged from 80 (Nyanzi et al. 2001) to 13,294 (Edwards et al. 2006b) and was on average 3011 participants. Almost all studies were cross-sectional. Only two longitudinal studies were found (Jewkes et al. 2016; Lee et al. 2016). Data collection methods varied, with most studies administering self-completed, paper-based questionnaires, and others online questionnaires, audio-computer assisted questionnaires, or structured face-to-face interviews using standardized questions. Out of all 37 studies, 19 were conducted in Sub-Saharan Africa, four in North America, 11 in Western Europe, and three in Asia.

Table 1 Studies on transactional sex with general population samples of youth Measurement

No standardized instrument currently exists for measuring transactional sex. Items used in the included studies typically referred to accepting money or gifts for sexual favors (selling sex) and giving money or gifts for sexual favors (buying sex). The types of gifts, such as drugs, cell phones, shelter, and food, were sometimes, but not always, specified in the items. In this article, transactional sex is defined as casual sex between two people that is motivated by the expectation to receive material rewards in exchange for sexual favors. The reference period was usually the past 12 months or the respondent’s lifetime, but it was not always reported. Table 2 provides examples of questionnaire items that have been used in existing studies on transactional sex. Although there have been exceptions (e.g., Jewkes et al. 2016), studies have typically used one or two items to measure either selling or buying sex. Thirty-five studies reported on selling sex and nine studies reported on buying sex (the total number of studies is higher as some studies reported on both). One study measured involvement in transactional sex, but it did not distinguish between selling and buying (Chatterji et al. 2005).

Table 2 Examples of questionnaire items to measure youth involvement in transactional sex

Below, prevalence estimates are presented first. The 37 studies included in this review provide prevalence estimates for 28 countries. The results from high-income countries are compared to results from low- and middle-income countries. Next, the situations and relationships surrounding transactional sex are described. Differences between country income groups are described where applicable. Subsequently, research on the correlates of involvement in transactional sex is presented.

Prevalence of Transactional SexHigh-Income Countries

The review identified 15 studies with prevalence estimates on transactional sex in seven high-income countries as defined by the World Bank (2017) (e.g., countries with a GNI per capita of $12,056 or higher in 2017). Most studies (11 out of 15) were conducted in Northern and Western Europe (Norway, Sweden, Denmark, Germany, and Netherlands); the remaining four in North America (the USA and Canada). Six studies used lifetime reference periods, two provided past-year rates, and seven did not report the reference period. Fifteen studies reported on selling sex and three studies reported on buying sex (the total number of studies is higher as some studies reported on both). Prevalence estimates are provided in Table 3.

Table 3 Prevalence rates of transactional sex in general population samples of youth in high-income countries

The results suggest that transactional sex is uncommon among youth in high-income countries. The highest overall selling rates among both male and female youth (combined rates) were reported in Germany (7%, reference period not reported), followed by Canada (4%, lifetime prevalence) and the United States (2.8%, reference period not reported, and 3.5%, lifetime prevalence), while prevalence rates in other high-income countries were lower.

With the exception of the study by Lavoie et al. (2010) in Canada, which reported that three times as many female (6%) compared to male (2%) youth had sold sex, prevalence rates of selling sex were higher among males than females. Six out of seven studies with data for both, male and female youth, reported higher selling rates for males compared to females, ranging from 1.7% (lifetime) to 2.6% (reference period not reported) for males and 0.6% (last 12 months) to 2.3% (lifetime) for females.

Only three studies examined buying sex. In the Netherlands, prevalence rates were 6% for male and 1% for female 12- to 25-year-olds. In the United States, a study among female youth showed that 4% had ever bought sex. Finally, Lavoie et al. (2010) reported buying rates of 5% among male and 2% among female youth in Canada.

Low- and Middle-Income Countries

The search identified 22 studies on transactional sex in 21 low- and middle-income countries as defined by the World Bank (2017) [e.g., countries with a GNI per capita of $995 or less (low-income countries) or between $996 and $12,055 (middle-income country) in 2017]. With the exception of one study in China, all were conducted in Sub-Saharan Africa. The higher number of studies may be due to the fact that transactional relationships are more widespread in these countries (Manganja et al. 2007; Nyanzi et al. 2001). Twelve studies used lifetime reference periods, four provided past-year rates, three studies used more than one reference period (e.g., lifetime, last 12 months, last 4 weeks), and two studies did not report a reference period. Twenty-two studies reported on selling sex while nine studies reported on buying sex. Prevalence estimates are provided in Table 4.

Table 4 Prevalence rates of transactional sex in general population samples of youth in low- and middle-income countries

Data suggest that transactional sex is relatively common among youth in Sub-Saharan Africa. The highest rate for selling sex among female youth was reported in Uganda (85%, lifetime prevalence). Particularly high prevalence rates were recorded in six countries, with over 60% of female youth reporting that they sold sex: Ghana (74.7%, last 12 months), Liberia (72%, lifetime), Malawi (80.5%, last 12 months), Mozambique (63%, reference period not reported), Tanzania (80%, lifetime), and Uganda (75%, last 12 months; 85% lifetime).

In contrast to high-income countries, where more males reported selling sex than females, all six studies that collected comparative data on selling sex for both sexes in Sub-Saharan Africa reported higher selling rates for female compared to male youth. Lifetime prevalence rates for selling sex among female youth in Sub-Saharan Africa ranged from 5% among 12- to 17-year-olds in Cameroon (Meekers and Calvès 1999) to 85% among 12- to 20-year-olds in Uganda (Nyanzi et al. 2001). Few studies examined lifetime prevalence rates for selling sex among male youth. Among those that did, lifetime rates ranged from 6.6% among 15- to 26-year-olds in South Africa (Dunkle et al. 2007) to 12% among 14- to 17-year-olds in Liberia (Atwood et al. 2012). Compared to these estimates, the multi-country study by Moore et al. (2007) showed relatively high prevalence rates for some countries (e.g., Ghana: 33.3%, Uganda: 34.6% for males), but this study used a past-year reference period in a sample of youth who had been sexually active in the past 12 months.

Only two studies explicitly asked about buying sex among female youth. These found that 6.2% (reference period not reported) of female youth in Uganda (Choudhry et al. 2014) and 8.2% (lifetime) in Liberia (Atwood et al. 2012) had ever bought sex. Lifetime prevalence rates of buying sex among males ranged from 14% in Cameroon (Meekers and Calvès 1999) and Liberia (Atoowd et al. 2012) to 60.4% in South Africa (Jewkes et al. 2012b).

There were substantial differences in prevalence estimates for some studies that were conducted in the same country, for example between studies in Liberia (Atwood et al. 2012; Okigbo et al. 2014), Malawi (Moore et al. 2007), South Africa (Dunkle et al. 2007; Jewkes et al. 2012a, b; Ranganathan et al. 2016; Zembe et al. 2015), and Uganda (Choudhry et al. 2014; Moore et al. 2007; Nyanzi et al. 2001; Population Reference Bureau 2001). These differences are due to different item wordings, reference periods, sampling strategies, and timing.

There were also large differences in prevalence rates between countries in Sub-Saharan Africa. Although these may be due to different sampling strategies and items, a cross-national study that used comparable methods across 12 countries in Sub-Saharan Africa (Chatterji et al. 2005; Rutstein and Rojas 2006) found large variations in prevalence rates. The rates reported for Sub-Saharan Africa also differed from those in a longitudinal study in China, where the combined lifetime prevalence for selling sex among females and males was relatively low at 0.2% (wave one, last 12 months), 0.4% (wave two, last 12 months) and 0.6% (wave three, last 12 months) among a sample of high-school students (Lee et al. 2016). One study suggested that there might be differences in prevalence rates among age groups that fall within the UN definition of youth. According to one study that compared aged groups in various countries in Sub-Saharan Africa (Chatterji et al. 2005), 15- to 19-year-olds were more likely to engage in transactional sex than 20- to 24-year-olds.

Situations and Relationships Surrounding Transactional Sex

The included studies were reviewed regarding the situations and relationships in which transactional sex occurred. Unfortunately, relatively few studies provided such information, making generalizations difficult. This section describes the characteristics on which there exists at least some evidence (e.g., mentioned in two or more studies). These include ways of establishing initial contact with buyers, forms of compensation, the age of onset, as well as characteristics of sex partners.

Initial Contact

The most common way in which sellers and buyers initiate contact appears to be through friends and acquaintances and, increasingly, online. In Sweden, both boys (35%) and girls (30%) were most likely to meet buyers via friends and acquaintances (Svedin and Priebe 2007). According to a Canadian study, over 90% of transactional sex happened between friends and acquaintances (Lavoie et al. 2010). Across Sub-Saharan Africa, male peers often act as intermediaries between female sellers and male buyers because of the social norm that men should start explicit sexual negotiations (Nnko and Pool 1997; WHO 1992). Dating websites are also a common way to initiate sexual relationships in some high-income countries, but it is unknown whether similar patterns hold for Sub-Saharan Africa. For instance, 23% of American and 57% of Swedish youth engaging in transactional sex reported that their initial contact with prospective buyers was online (Fredlund et al. 2013; Curtis et al. 2008).

Types of Compensation

Money seems to be the most common form of compensation. Across four countries in Sub-Saharan Africa, 93% or more of female youth involved in transactional sex reported that they received money for sexual activities, followed by clothes, jewelry, and cosmetics (Moore et al. 2007). Similar findings were reported in a South African study among male buyers of sex, where half reported exchanging cash for sexual favors rather than other types of compensation (Jewkes et al. 2012b). In Sweden, the majority of youth reported receiving money as a payment for sexual activities (Svedin and Priebe 2007; Fredlund et al. 2013). In contrast to teenagers in Sub-Saharan Africa, however, Swedish youth also frequently received alcohol and cigarettes (24%) or drugs (20%) in exchange for sexual favors (Fredlund et al. 2013).

Age of Onset

The evidence on the age of onset is still limited, but existing research from high-income countries suggests that the majority of youth was between 13 and 15 years old when they first engaged in transactional sex. For example, in a Canadian study of adolescents aged 15 to 18, 57% of buyers were between 14 and 15 years old, while 63% of sellers were aged 13 to 15 years (Lavoie et al. 2010). Similarly, in a Swedish study, the mean age of onset among boys and girls who received sex for money or gifts was 15.6 years (Svedin and Priebe 2007). It is unclear whether this age pattern holds in low- and middle-income countries.

Characteristics of Sex Partners

Studies across various countries have found that less than a quarter of girls who had sold sex had partners that were more than 10 years older than themselves (Luke and Kurz 2002; Nnko et al. 2001; Gregson et al. 2002; Görgen et al. 1998; Kelly et al. 2003; Kekovole et al. 1997; Lavoie et al. 2010; Chatterji et al. 2005; Matasha et al. 1998; Kaufman and Stavrou 2004; Nyanzi et al. 2001). For example, Svedin and Priebe (2007) reported that about half of all buyers were of a similar age as the sellers (between 15 and 25 years old), whereas roughly one-third of buyers was aged 26–35 years, and the remainder was older than 36 years.

Correlates of Transactional SexSexual Behavior

Findings suggest that youth involved in selling sex are more promiscuous, have an earlier sexual debut, and are more likely to consume pornographic content. Studies in different regions of the world have found a significant link between selling sex and having a higher number of sexual partners (e.g., Betzer et al. 2015 for Germany; Svedin and Priebe 2007 for Sweden; Pedersen and Hegna 2003 for Norway; Edwards et al. 2006b for the USA; Atwood et al. 2012 for Liberia; Dunkle et al. 2007 for South Africa; and; Moore et al. 2007 for Uganda). However, a study in Ghana found a significant relation between selling sex and a lower number of sexual partners (Moore et al. 2007). The link between buying sex and a higher number of sexual partners has not been systematically studied.

Early sexual debut has also been associated with selling sex (Lavoie et al. 2010; Pedersen and Hegna 2003; Okigbo et al. 2014; Svedin and Priebe 2007). In Sweden, the average age of first intercourse for youth aged 14 to 18 who had sold sex was 14.4 years, which was significantly lower than for those who had not sold sex (15.6 years) (Svedin and Priebe 2007). While this study did not find gender differences, a Norwegian study reported that the association between selling sex and debut age was stronger in girls than boys (Pedersen and Hegna 2003). It is unknown whether the same pattern holds for buying sex.

Finally, the consumption of pornographic content or the observation of sexualized activities has been associated with the likelihood of selling sex. In Sweden, boys and girls who had sold sex watched online pornography more frequently than those who had not sold sex: 38% of boys who had sold sex watched pornography every day as compared to 9% in the reference group (Svedin and Priebe 2007). This study also found some gender differences in the type of porn being watched. Boys who had sold sex were more likely to watch porn involving violence, force, animals, and children compared to boys who had not sold sex, but the groups did not differ in their consumption of ordinary porn (e.g., non-violent sex between adults). Girls who had sold sex reported to have watched both ordinary and deviant types of pornography more often than girls who had not sold sex. In Canada, Lavoie et al. (2010) examined the association between transactional sex and promiscuity—measured through the observation of participation in nine sexualized social activities (these included wet T-shirt contests, striptease, same-sex kissing, imitation of fellatio with an object, dance contests in which people mime sexual positions, fellatio contests, group sex, and group masturbation). They found that while promiscuity was also significantly associated with buying sex for both genders, it was not linked to selling sex.

Substance Use

The use of legal and illegal substances has been widely shown to be associated with selling and buying sex (Betzer et al. 2015; Edwards et al. 2006b; Svedin and Priebe 2007; Choudhry et al. 2014; Dunkle et al. 2007; Pedersen and Hegna 2003; Okigbo et al. 2014; Lee and Shek 2013). For example, compared to other young people, American youth who had sold sex were significantly more likely to have ever consumed marijuana (54% vs. 35%), cocaine (24% vs. 4%), injection drugs (11% vs. less than 1%), and other illicit drugs (30% vs. 10%) (Edwards et al. 2006b).

In addition, studies in Sweden, Norway, and Liberia found strong correlations between a higher frequency of alcohol consumption and selling sex for both girls and boys (Svedin and Priebe 2007; Pedersen and Hegna 2003; Okigbo et al. 2014). In Liberia, 30.5% of girls who had ever engaged in transactional sex reported daily use of alcohol, compared to 13.1% in the reference group (Okigbo et al. 2014). However, studies in Germany, Uganda, and Canada found no such association (Betzer et al. 2015; Choudhry et al. 2014; Lavoie et al. 2010). Problematic alcohol use was also associated with buying sex among boys in South Africa (Dunkle et al. 2007) and Uganda (Choudhry et al. 2014). No relationship was found between buying sex and alcohol problems among Ugandan girls (Choudhry et al. 2014).

While there is some evidence for an association between substance use and selling sex, there is disagreement about the directionality. Substance use could be a consequence of involvement in transactional sex, as substances may numb the feelings of guilt and shame that were reported to accompany transactional sex in a Dutch study, particularly among girls (Walle et al. 2012). However, transactional sex could also be a means to finance addictions or a manifestation of psychosocial difficulties. The association between buying sex and substance abuse has not been systematically researched.

Sexual and Mental Health

Studies have consistently found statistically significant relations between sexually transmitted diseases and selling sex among both boys and girls (Betzer et al. 2015; Jewkes et al. 2012a, b; Atwood et al. 2011; Edward et al. 2006a, b). This may be due to the higher number of sexual partners among youth involved in transactional sex that was documented in various studies (e.g., Betzer et al. 2015 for Germany; Svedin and Priebe 2007 for Sweden; Pedersen and Hegna 2003 for Norway; Edwards et al. 2006b for the USA; Atwood et al. 2012 for Liberia; Dunkle et al. 2007 for South Africa; and; Moore et al. 2007 for Uganda). A study by Norris et al. (2009) suggests a possible link with substance abuse: Youth who traded sex and abused alcohol had a significantly higher risk for sexually transmitted diseases compared to those who exchanged sex but did not have alcohol problems. It is unknown whether this pattern holds for youth who buy sex.

Youth who sell sex also display an elevated risk of mental health issues and depression (Choudhry et al. 2014; Edwards et al. 2006b; Reid and Piquero 2014; Pedersen and Hegna 2003; Svedin and Priebe 2007). In a Swedish study, more than half of female youth who sell sex reported that they felt that ‘everything was a struggle,’ had troubles sleeping, and felt unhappy, miserable, depressed, tied up, or tense (Svedin and Priebe 2007). Similarly, 22% of male and female sellers of transactional sex in an American study reported that they felt depressed, compared to 11% of youth who did not sell sex (Edwards et al. 2006b). This association was not studied for youth who buy sex.

Family Characteristics

Alcohol abuse at home can increase the likelihood of selling sex in both genders (Pedersen and Hegna 2003; Reid and Piquero 2014). For example, in a Norwegian study of youth aged 14–17 years, exposure to alcohol at home was twice as high in boys and girls who sold sex compared to the rest of the sample (Pedersen and Hegna 2003). Research has not examined the link between alcohol abuse at home and buying sex.

Studies in Sub-Saharan Africa, Sweden, and Norway found that growing up with a single parent or non-parental caretakers increased youth’s likelihood to sell sex (Choudhry et al. 2014; Fredlund et al. 2013; Pedersen and Hegna 2003). In Sweden, 48% of students who sold sex lived with both parents as compared to 61% of those who did not sell sex (Svedin and Priebe 2007). In Hong Kong, students with remarried parents reported significantly higher frequencies of transactional sex compared to those whose parents remained in their first marriage (Lee and Shek 2013). Also, being abandoned by both parents or living in orphan care has been linked to selling sex (Okigbo et al. 2014; Svedin and Priebe 2007; Moore et al. 2007). The association between buying sex and family break-up has not been systematically researched.

Findings on the influence of parenting style and family functioning on selling sex have been more mixed. Some studies have found a significant relation. For example, Fredlund et al. (2013) found that Swedish boys and girls who sold sex reported overly strict parenting, poorer parental care, and more difficulties sharing problems with family members and friends. Higher levels of family functioning, in turn, may be a protective factor (Lee and Shek 2013). In contrast to these findings, some studies found no significant difference in family functioning between youth who sold sex compared to youth who did not sell sex (Lee et al. 2016; Moore et al. 2007; Pedersen and Hegna 2003). Parenting style and family functioning have not been studied for adolescent buyers of sex.

History of Violence in Childhood

One of the most widely examined correlates for transactional sex is being a victim of violence or abuse in childhood. Experiences of forced sexual activity in childhood have been related to buying and selling sex in both genders (Lavoie et al. 2010; Edwards et al. 2006b; Svedin and Priebe 2007; Okigbo et al. 2014; Choudhry et al. 2014; Dunkle et al. 2007). According to Edwards et al. (2006b), 17% of American girls and 10% of boys who had ever been forced into sexual activity sold sex, compared to 8% of girls and 2% of boys without such experiences. In a Swedish study, the majority (62%) of boys and girls who sold sex reported that they had experienced sexual abuse before they started selling sex (Svedin and Priebe