STDs often go undetected or untreated among young women, who, embarrassed or stigmatized by the presence of a STD, are reluctant to seek help. Yet STD agents, such as Chlamydia and human papilloma virus, can have dire consequences at later times, such as infertility or cervical cancer. Worldwide, more than half of all new HIV infections occurs in the 15 to 24 age group. Although young people may know how AIDS is transmitted and prevented, many believe their risk of infection is minimal. Girls appear to have a significantly higher incidence of HIV infection than boys.
Tobacco use is another serious health problem for adolescents.
Swayed by images of adult smokers or through advertising, young people perceive smoking to be sophisticated or fun. One third to one half of young people who experiment with cigarettes become regular smokers, half of them within one year. Teens who smoke daily for a number of years develop a habit and addiction level as difficult to reverse as for adult smokers. Although many try repeatedly, very few adolescents actually stop smoking. Studies show that young people who do not use tobacco before the age of 20 are unlikely to start smoking as adults.