INTRODUCTION The World Health Organization (WHO) considers adolescence to be the stage of the life cycle that encompasses the age range between 10 and 19 years. It begins with the bodily changes of puberty and ends when the individual consolidates his or her growth and personality, progressively achieving economic independence. This period is characterized by a transition phase between childhood and adulthood, marked by intense physical and psychosocial transformations. In Brazil, 15.16% of the population is between 10 and 19 years old, of which 7.73% are male and 7.43% are female ¹ . It is important to know these data, because in Brazil the pregnancy rate is above the Latin American average for adolescents aged 15 to 19 years, with this number being 68.4 for every thousand adolescents in Brazil, 65.5/1000 in Latin America, and the average worldwide is 46/1000 ² . The vast majority of sexually transmitted infections are not subject to mandatory reporting, and there is little data on their epidemiology and, even among specific data, there is likely underreporting among adolescents. The importance of understanding the sexual behavior of adolescents lies in the context of health and education, in order to adapt public policies related to sexual and reproductive health, such as preventing the transmission of sexually transmitted infections and unplanned pregnancies, in addition to vaccination campaigns, such as against the human papillomavirus, and addressing this issue in schools with the aim of minimizing vulnerability at this stage of life. In particular, pediatricians, gynecologists and family doctors need to know the factors that can lead to early sexual initiation in order to recognize them and promote dialogue between adolescents and their families, to avoid risky behaviors and promote healthy sexuality throughout life. In South Korea, in 2012, for example, it was observed that condom use decreased in those who initiated sexual activity before the age of 16, compared with those who initiated it after this age, with an Odds Ratio (OR) of 1.79 for boys and 4.37 for girls ³ . In another study, conducted in the cities of Porto Alegre, São Paulo and Campinas, an earlier than average sexual initiation was associated with a higher HPV infection and cytological alterations in the Pap smear ⁴ . The objective of this study is to analyze the sexual behavior of patients treated at an Adolescent Outpatient Clinic of a public university hospital. METHODS This is an analytical, observational, cross-sectional study of data from the CLAP-OPS/WHO (Latin American Commission on Pediatrics/Pan American and World Health Organization) Adolescent History form. The study included all patients (n = 1,400) treated at the Adolescent Outpatient Clinic of the Hospital de Clínicas of the Federal University of Paraná between 2006 and April 2018. The profile of these patients is adolescents between 10 and 20 years of age, referred to the Hospital de Clínicas by the Municipal Health Department, in the majority, or by the State Health Department. The instrument was applied in the first consultation at the Outpatient Clinic (attached). All completed forms were included in the study, however, only completed fields were considered for analysis. Questions regarding lifestyle habits, sexuality, and body image were asked alone with the adolescent, asking the companion to leave the office, respecting the principles of secrecy and confidentiality. The statistical tests used were the Kruskall-Wallis, Fisher’s exact, Mann-Whitney, chi-square and Spearman correlation tests, calculated using the R Core Team 2018 software . RESULTS A total of 1,400 adolescents were seen, 853 (62%) were female and 521 (38%) were male. The median age was 15 years for females and 14 for males. The age group of 14 to 17 years was the most prevalent, with 612 (44.15%) adolescents. The majority were from Curitiba and the mother attended the first consultation in 56.9% of cases (Table 1). The educational level of parents or guardians was incomplete elementary school (48.5%) followed by high school (30.5%). Among the patients, 86% were studying, 37.4% had failed at least one year of schooling, and 12% had dropped out of school, in addition to 31% being employed. The median age at menarche or spermarche was 12 years. The adolescents did not have regular cycles in 40.63% of cases, and 15% did not know the date of their last menstruation. Sexual abuse was reported in 21 cases, 19 (90.5%) by girls. Most patients (62.8%) reported that they had not initiated sexual activity, with no significant difference between the sexes. The incidence of sexarche varied according to the age group analyzed: in the group in the early adolescence range (10-13 years), only 4.1% had had intercourse (4.9% of girls and 3.1% of boys); in the middle adolescence range, 30.2% (30.2% of girls and 30.2% of boys); and in late adolescence the incidence rose to 62.6% (64.2% of girls and 59.4% of boys). The frequency of sexual initiation was higher among those who reported having a boyfriend (72.7%), and lower in the group with impaired body image and those with abnormal development (21%). The mean and median ages at first sexual intercourse were 13.7 years and 15 years, respectively. The median age at first sexual intercourse was 14 years for boys and 15 years for girls. Regarding the type of sexual intercourse, 96% reported having heterosexual relationships, 4% had homosexual or bisexual relationships. There were no differences in the median age at first sexual intercourse among those who had heterosexual or homosexual relationships or both types (p<0.001). The majority (88.1%) had a single partner and 47.2% always used hormonal contraception and 13.36% sometimes used it. However, 53.5% of adolescents used condoms in all sexual relations, 26.1% used them occasionally and 20.4% never used them, although 81.8% claimed to have information about sexuality. 2% of the interviewees had a history of abortion or pregnancy. The factors that led to a reduction in the age of sexual initiation were: male gender, domestic violence (p=0.006), child of a teenage mother (p=0.03), personal (p<0.001) and family (p=0.025) legal problems, personal (p=0.0012) and family (p=0.03) psychological disorder, and work (p<0.001) (Table 2). All these factors led to a reduction in the median age of first sexual intercourse of 1 year (from 15 to 14 years), except for legal problems, where this reduction was even more significant (2 years). The number of partners, type of sexual relationship (heterosexual, homosexual or bisexual), incidence of problems during sexual intercourse, whether or not students were enrolled, and problems with alcohol or drugs in the family did not influence the age of sexual initiation. The age at which alcohol use began (rho=0.4785) and work began (rho=0.4691) had a moderate impact on sexual initiation. The use of illicit substances was associated with a higher incidence of multiple sexual partners (p<0.001). Of the patients who did not use illicit substances, 22% had multiple sexual partners, with the rate rising to 70% among users of these substances (p<0.001). DISCUSSION The incidence of sexual intercourse obtained in this study was higher when compared to the results of the National School Health Survey (PeNSE) ⁵ , conducted by the Brazilian Institute of Geography and Statistics, and the Study of Cardiovascular Risk in Adolescents (ERICA) ⁶ . This can be explained by the inclusion of adolescents up to 20 years of age in the sample of the present study, while in the aforementioned studies, adolescents up to 17 years of age were interviewed, since the older the age, the greater the chance that the young person has already had sexual relations. The fact that the incidence of first sexual intercourse is higher in the group that reported having a boyfriend/girlfriend may indicate that most adolescents have their first sexual intercourse within a romantic relationship ⁷ . The median age at the time of first sexual intercourse was 15 years, slightly below the average found in the review conducted by the Lancet ⁸ journal in 2006, which was 16.5 years. At the time, the average age of first sexual intercourse ranged from 17.3 to 18.5 years in industrialized countries. This outcome can be explained by the decrease in the average age of sexual initiation in the last 12 years and by the fact that the sample reflects a portion of the population from public schools, which has a higher rate of first sexual intercourse in all age groups analyzed by the National School Health Survey ⁵ . The difference between developed and developing countries is very clear in the study carried out by Taquette (2012) ⁹comparing Brazil and France. This study showed that the age of sexual debut in France is 17.5 years and 18 years for males and females, respectively. Since 2001, a program established by law has required three annual sessions of sexual and emotional education in schools. The use of contraception is more frequent than found in our study, occurring in 87.6% of male adolescents and 84.2% of females at the time of their first sexual intercourse. In contrast, in Brazil, where these policies are not consistent, the median age of first sexual intercourse is 15 years for girls and 14 years for boys. In addition, the French have access to specific health services for adolescents with a multidisciplinary team, laboratory and imaging tests, contraceptives, and sexual education. In a literature review of 36 studies, it was demonstrated that girls who delayed their first sexual intercourse until the age of 16 were physically and psychologically healthier than those who initiated their sexual life before the age of 16, and that adolescents who had intercourse at the age of 14 or earlier had a higher risk of depression and lower self-esteem ¹⁰ . In another study, girls who had their first sexual intercourse before the age of 17 were more likely to have depression, with an odds ratio of 2.29 ¹¹ . Thus, it is difficult to establish whether the psychological disorder is a cause or a consequence of early sexual initiation. A meta-analysis of 50 studies showed that early puberty can lead to an earlier sexual debut ¹² . However, this relationship was not significant in our study. This shows that, in addition to the age of menarche and spermarche, it is important for adolescents to have a good perception of their own body, their body image, and good self-esteem, which explains the lower frequency of sexual intercourse in the group that has difficulty with body image, harming their relationships with others. The relationship between an absent father between the ages of 6 and 13 and an earlier sexual debut for girls was also evidenced in the study by Georgetown University, which explained this finding as a function of less parental monitoring ¹³ . Another study, conducted in the Netherlands, with 5,642 adolescents aged 12 to 16, concluded that stricter and more concrete rules of conduct on the part of parents prevent not only an earlier sexual debut but also alcohol and tobacco consumption ¹⁴ . This evidence corroborates that domestic violence, psychological disorders, and family legal problems contribute to earlier sexual initiation, as observed in our study, due to the low level of care provided to adolescents by their parents and/or a worse relationship between adolescents and their families. Nogueira et al. (2018) ¹⁵ concluded that, in the Netherlands, a quality relationship between adolescents and their parents, especially between mothers and daughters, can help protect against early sexual initiation. Considering the fact that 56.9% of patients came to the consultation accompanied by their mothers, they are the ones who play a greater role in the health of their children. In their study on the relationship between mothers and children, Price et al. (2018) ¹⁶ concluded that mothers play an important role in determining the age of sexual initiation of their adolescent children. Furthermore, some publications indicate that being raised by a mother who had children in adolescence can lead to an active sexual life at a younger age or pregnancy in this age group ¹⁷ . Other studies corroborate our findings that mothers with depressive symptoms ¹⁸ and alcoholism ¹⁹ can lead to the same outcome in their children. The relationship found between the age at which alcohol consumption began and the age at which sexual intercourse began is worrying, since the first sexual intercourse under the influence of alcohol was associated with risky partners, greater chances of non-consensual relationships, and less positive evaluations ^19,20 . In a survey conducted with university students from the city of Beirut, 10% of the interviewees admitted to having used alcohol or drugs before their first sexual experience ²⁰ , with twice the chance of engaging in some type of sexual act that they did not want. In another study, conducted with high school students from Curitiba, 47.3% reported having used alcohol before having sexual intercourse ²¹ . The use of some type of contraceptive method is rare, since hormonal contraception was used by less than half of the sexually active adolescents (47.17%). Condoms are not remembered by adolescents in Brazil, as their use was detected in all sexual relations in 53.47% and sporadic in 26.08%. In the study carried out in the same city, Dallo et al. (2018) ²¹ detected that condom use was 81%, a value much higher than that of our sample. They found, however, a decrease to 41.7% among students who consumed alcohol during their first sexual intercourse ²¹ . In addition to alcohol use, tobacco also has a correlation with lower condom use, as observed by a study from South Korea with an odds ratio of 1.49 ³. It was found that adolescents who had sex before the age of 16 are less likely to use condoms, with an odds ratio of 1.79 ³ . The number of sexual partners was influenced by the use of illicit substances, corroborated by a study conducted in Pelotas – Rio Grande do Sul ²² , in which the increase in the number of sexual partners among young people who had used drugs in the last month was greater than those who had not used any illicit substance, with an odds ratio of 1.82. The use of licit and illicit substances usually combine, and are not isolated facts, which further increases the risk factors for multiple sexual partners. We conclude that sexual initiation remains early, in middle adolescence, with low adherence to contraception and prevention of sexually transmitted infections, and that family factors that lead to less parental control and a poor parent-child relationship can lead to the first sexual intercourse being about a year earlier. It is worth noting that the possible risk factors studied are not isolated in each patient, but add to each other, having a cumulative effect. Preventive interventions, an intersectoral approach to promote human rights with access to health services for adolescents, quality education with longer schooling, safety, sexual education, in addition to equitable development, combating early marriage and involving adolescents and young men are necessary ²³ .