INTRODUCTION Adolescence is a stage of human growth and development, situated between childhood and adulthood, marked by physical, psychological and social transformations, and defined by the United Nations as the age range from 10 to 19 years of age ¹ . The early onset of sexual life among adolescents is an increasingly noticeable characteristic, and these young people may encounter unusual situations such as Sexually Transmitted Infections (STIs) and contamination by the Human Immunodeficiency Virus (HIV)/Human Immunodeficiency Syndrome (AIDS). In addition, it is during adolescence that sexuality manifests itself most clearly, and due to the young person’s lack of preparation to deal with this aspect, not only do the risks of STI infection increase, but the chances of an unwanted pregnancy also increase ^2-3 . Since the beginning of the AIDS epidemic in 1980, until June 2014, Brazil had 756,998 registered cases of HIV/AIDS. The highest concentration of cases in Brazil is in the 25-39 age group, but 81,205 of the cases occurred in the 15-24 age group. In the last 10 years, there has been an increase in the detection rate, with an increase in incidence of 53.2% among young people aged 15-19 and 10.4% in the 20-24 age group ⁴ . Regarding teenage pregnancy, in 2013, approximately 20% of live births were to teenage mothers ⁵ . Prevention and contraception methods are known by a large part of the population of reproductive age, as well as by health professionals and educators. However, the issue of the effectiveness and use of these methods is not always explored among adolescents, and this information is extremely important for prevention practices ⁶ . Brazil is a large country with a diverse cultural, social and economic population. Therefore, understanding the views of young people from different locations on the factors involved in reproductive planning and STIs is essential for structuring and implementing strategies that serve adolescents equally. OBJECTIVE To describe the knowledge about contraceptive methods and sexually transmitted infections among adolescents in public schools in the city of Senhor do Bonfim, Bahia (BA). METHODS This is a descriptive study with a quantitative approach, carried out in state schools in the urban area of ​​the city of Senhor do Bonfim – BA, and consists of an excerpt from a research project entitled “Adolescence and Sexuality”. A total of 185 adolescents were surveyed. The initial proposal was to conduct a census and study the 457 students enrolled in the third year of high school in three schools who met the inclusion criteria. However, the high dropout rate observed in the classrooms made it impossible to survey all adolescents aged 14 to 19. The inclusion criteria considered were: adolescents of both sexes, aged 14 to 19, regularly enrolled in the third year of high school in three state schools located in the urban area of ​​the municipality of Senhor do Bonfim in 2014. Data were collected through a self-administered structured questionnaire, developed from a literature review and a questionnaire produced by the World Health Organization to assess the health of adolescents ⁷ . A pre-test was conducted with 17 high school students from one of the state schools, and the instrument was subsequently adjusted according to the demands that arose during its application. The final questionnaire consisted of 52 questions, divided into five blocks: 1) socioeconomic and family characteristics; 2) sources of information and knowledge about reproductive health; 3) relationships and use of contraceptives; 4) knowledge about HIV/AIDS and STIs; 5) condoms, knowledge and attitudes. Of these 52 questions, 29 addressed aspects of adolescents’ knowledge regarding sexual education, contraception and STIs. The questionnaire was administered to adolescents in their respective classrooms. Initially, the young people were guided by the researchers about the objectives of the study, completed the instrument, and, upon acceptance to participate in the research, read and signed the Free and Informed Consent Form (TCLE) (young adults) and the Assent Form (young minors). In relation to minors, a prior meeting was held with their parents and guardians where they signed the TCLE to authorize the young person’s participation in the study. Data collection was carried out between September and November 2014. The research was approved by the Research Ethics Committee of the State University of Bahia, based on Resolution No. 466/2012 of the National Health Council, and received approval report No. 558.605. The collected data were stored in a database, processed and analyzed in the Statical Package for Social Sciences program.(SPSS) version 9.0. In the first stage, with the objective of evaluating the quality of typing, an analysis of the consistency of the database was carried out with the listing of the simple frequencies of the variables and subsequently the typing errors found were corrected. Then, an exploratory and descriptive analysis of the sample studied was developed through the calculation of the absolute frequencies of the variables researched. RESULTS The study consisted of 185 adolescents in the age range of 16 to 19 years old, with no young people under 16 years old in the classes researched. Table 1 presents the sociodemographic characteristics of the group studied, where 83.3% (n=150) lived in the urban area, 60% (n=111) were female, 31.4% (n=58) were aged between 16 and 17 years, 93.0% (n=172) had no children, 72.3% (n=133) considered themselves black/brown, 88.0% (n=162) were single, 55.5% (n=102) called themselves Catholic and 79.2% (n=145) had a monthly family income of less than one minimum wage. Table 2 presents the results regarding the source of information about sexuality, observing that for a third of young people, parents are the main source of information about sexuality. 78.4% (n=145) reported that they had already attended a class on sexuality and 96.2% (n=178) said that they should have more classes on sexuality at school. Regarding knowledge about family planning and STI prevention, Table 3 shows that for 68.2% (n=116) of those surveyed, condoms are the most appropriate method to prevent teenage pregnancy. Regarding the known mechanisms to prevent STIs, 98.9% (n=182) mentioned condoms. Regarding knowledge regarding STIs and their symptoms, Table 4 shows that 98.4% (n=182) of students had already heard about HIV/AIDS and, regarding the symptoms an individual with an STI could present, approximately two thirds indicated the presence of ulcers, wounds and itching on the penis or vagina. Table 5 shows the opinion on aspects related to STIs and condom use. 38% (n=69) of the adolescents reported that STIs can be transmitted by sharing the same toilet and/or towel, 13% (n=23) agreed that STIs can be transmitted by sitting in the same place as the infected person. It was observed that 45% (n=81) indicated that condoms reduce the pleasure of sexual intercourse, 30% (n=56) stated that condoms can come off the penis and disappear inside the woman’s body during sexual intercourse. For 19.9% ​​(n=36) of the young people, condoms are suitable for use only in occasional intercourse, 17.7% (n=32) agreed with the statement that using two condoms at the same time increases the chance of prevention (Table 5). Among those surveyed, 9% (n=16) agreed that there is no need to use a condom during the first intercourse, as there is no risk of pregnancy, 5.5% (n=10) stated that there is no need to use a condom during the first intercourse because there is no risk of STI infection (Table 5). DISCUSSION In the present study, the main source of information about sexuality cited by the young people was their parents (34.1%, n=58). In a study conducted in the city of Bauru-SP with students from a public school, the proportion of young people who had their parents as their main source of information was even higher (82%) ⁸ . Until recently, topics related to sexuality were considered taboo within families, and were reprimanded and silenced. Currently, in some families this topic has been discussed transparently through dialogue and seeking professional support, when necessary ⁹ . The figure of the teacher ranked sixth in relation to sources of information, which differs from studies conducted in Goiânia-GO and Great Britain, where approximately 80% of young people reported that the main place for information about sexuality is school ^10,11 . The fact that teachers were not among the most important sources of information in the present study is worrying, which raises questions about the importance of the school in fulfilling its social function as an educator, in addition to being a space for adolescents to interact daily, and should be a place where young people can bring and clarify doubts and questions, especially those related to sexuality. It is also noticeable that the media plays an important role in the acquisition of knowledge regarding aspects related to sexuality, with the Internet taking second place in relation to the main sources of information for young people in the schools surveyed. The media are widely disseminated and the value attributed to them can be worrying, as they are not the most appropriate mechanisms for obtaining sufficient clarification on the subject ¹⁰ , since often misleading information is disseminated and the approach is not always appropriate for raising awareness among young people. Almost all of the adolescents studied indicated the need for more classes on sexuality in schools. In a survey conducted with students from a state school in São Paulo, 54.7% of the young people said that the school does not provide sexual orientation ³ . In addition to the lack of activities that discuss aspects related to sexuality, when these activities are developed, schools direct the discussion towards a biological focus, where the subjective dimension of sexuality is left aside, making the knowledge acquired distant from what is experienced by the student, and this approach usually does not correspond to the expectations regarding the doubts and questions of adolescents ³ . Regarding the methods that they consider most appropriate for contraception in adolescence, the condom was the most cited (68.2%, n=116). However, it is important to emphasize that simply mentioning the method does not necessarily mean that there is appropriate knowledge about its use, advantages, disadvantages and forms of access ¹² . Regarding known methods for preventing STIs, condoms were also mentioned by almost all of the students analyzed (98.9%, n=182). A similar result was observed in a study conducted in two public schools in Rio de Janeiro-RJ ⁵ . Although young people have some knowledge about how to prevent STIs, there is a growing trend of AIDS in the young population ⁵ . Thus, reinforcing concepts about STIs and HIV/AIDS can enable the process of reflection and action by adolescents, reducing their vulnerability to these diseases ¹³ . The most well-known STI among the group studied was HIV/AIDS (98.4%, n=182), a fact observed in other studies conducted in Araçatuba-SP and Canoas-RS, where 91.2% and 92.3%, respectively, of the young people knew about this pathology ^14-15 . Regarding other types of infections, more than half of the young people reported knowing about Gonorrhea, Syphilis, Hepatitis, Genital Herpes and Human Papillomavirus (HPV) as sexually transmitted diseases. In a study conducted in Araçatuba-SP, it was found that most young people reported knowing about HIV/AIDS, Herpes, HPV, Gonorrhea, Syphilis and Condyloma ¹⁴ . Thus, it can be seen that these adolescents know an average of five to six STIs, which shows a good level of information regarding existing infections. Regarding knowledge about the symptoms that an individual may present when acquiring an STI, more than half of the young people mentioned, in decreasing frequency, the following: ulcers and wounds, itching, discharge – whether on the penis or vagina, and pain when urinating. A survey conducted with students from Embu-SP showed that the presence of wounds on the genitals was also the most frequently reported symptom, followed by discharge and itching in these organs ¹⁶ , corroborating the present study as the three most well-known signs and symptoms. Knowing the most common signs and symptoms resulting from STI contamination can contribute to adolescents’ self-care, since recognizing the symptoms represents an alert to seek health services for diagnosis and treatment. It is important to highlight that the present study observed the existence of myths, prejudices and fantasies involving issues of sexuality, such as the possibility of STI contamination by sharing the same towel or by sitting in the same place as the infected person. Misconceptions, combined with lack of information and biological conditions, increase the vulnerability to STI transmission in adolescence ¹⁷ . Furthermore, the dissemination of misconceptions about STI contamination can lead to prejudiced behavior in cases where the person carrying the infection is known, which can generate stigma in these young people, which can lead to psychological and social consequences in the adolescent’s life. Almost half of the young people indicated that condoms reduce the pleasure of sexual intercourse. In a study with students from a municipal school in Canoas-RS, it was observed that 28.5% of the adolescents considered that condoms interfere negatively with sexual pleasure ¹⁵ . It should be noted that opinions like these can contribute to adolescents abandoning condom use. The idea that condoms are suitable for use only in casual relationships was reported by 9.9% (n=36) of those surveyed. This concept was corroborated by a study with young people enrolled in public schools in the state of Paraíba, which showed that condom use was also associated with occasional partners ¹⁸ . Thus, it is observed that the type of emotional involvement, such as the relationship status of “hooking up” or dating, can interfere with condom use, and that condoms, in addition to being seen as a barrier to sexual pleasure, can be associated with infidelity or distrust, being used only in relationships with “unknown” partners ¹⁹ . Another important issue was regarding the first sexual intercourse and the non-use of condoms, as some interviewees stated that women do not have a risk of becoming pregnant (9%, n=16) or of acquiring STIs (5.5%, n=10) during their first sexual intercourse. The non-use of condoms, in addition to being associated with inexperience and difficulty in handling, also occurs due to the presence of beliefs that it is not possible to become pregnant or become infected with STIs during the first sexual intercourse ²⁰ . The use of contraceptive methods depends on a series of factors, including financial issues and access to methods, as well as the degree of freedom and autonomy achieved during adolescence. The study’s limitations include the fact that some young people did not answer some of the proposed questions. In research with adolescents, there is a possibility that participants do not answer the questions reliably, especially those related to the beginning of sexual intercourse, number of partners and use of contraception and prevention methods, because even though confidentiality is guaranteed in the research, adolescents may fear that aspects related to their intimacy will be discovered. The high school dropout rate was another limitation that made it impossible to study a larger sample. CONCLUSION The study shows that parents play a leading role in the sexual education of their children during adolescence, and it can be seen that the family has been gaining space and notoriety in discussions about sexuality with young people. However, the school did not play a relevant role in relation to sexual education in this study, and the young people themselves demonstrated the need for more classes and activities on the subject. It is also necessary to evaluate the role of the media in disseminating this information to adolescents, because in a context of easy and quick access to diverse information, this information can both help in the dissemination and construction of knowledge, as well as not being a sufficient source of clarification, and can generate doubts and ambiguous and imprecise understandings regarding sexual aspects. It was observed that adolescents have adequate knowledge about methods of STI prevention and contraception, but some still show mistaken knowledge, such as the belief that there is no possibility of acquiring an STI or becoming pregnant during the first sexual intercourse. In this context, it is necessary to understand the knowledge of adolescents and identify the gaps present, so that strategies can be structured and implemented by families, schools and health professionals, improving the sexual education of these young people, thus reducing the risks of unwanted pregnancy and contamination by STIs.