Sexual abstinence is the practice of refraining from some or all aspects of sexual activity for medical, psychological, legal, social, financial, philosophical, moral or religious reasons. For the last twenty years, abstinence rates among American adolescents have risen. The percentage of high school students in the US who reported that they have ever had sexual intercourse dropped from 54.1% in 1991 to 47.8% in 2007, 43% in 2011 and 39.5% in 2017. A cross-sectional survey in 1998 found that fear of pregnancy was the most commonly cited reason for choosing abstinence, especially among girls, as well as boys who had caused a pregnancy in the past. Other reasons included a fear of sexually transmitted infections, a lack of desire, being afraid of getting caught, and the belief that sex was not appropriate for someone of their age.