In humans, mature sexual desire usually begins to appear with the onset of puberty. Sexual expression can take the form of masturbation or sex with a partner. Sexual interests among adolescents, as among adults, can vary greatly. Sexual activity in general is associated with various risks including unwanted pregnancy and sexually transmitted infections including HIV/AIDS. A condom may be used to prevent pregnancy or sexually transmitted infections. There are also other safe sex options and contraceptives.

The risks are elevated for young adolescents because their brains are not neurally mature. Several brain regions in the frontal lobe of the cerebral cortex and in the hypothalamus that are deemed important for self-control, delayed gratification, risk analysis, and appreciation are not fully mature. The brain is not fully mature until age 25.^[2]Partially, because of this, young adolescents are generally less equipped than adults to make sound decisions and anticipate consequences of sexual behavior,^[3] although brain imaging and behavioral correlation studies in teens have been criticized for not being causative thus possibly reaffirming cultural biases.