Sexually transmitted infections (STIs), also referred to as sexually transmitted diseases (STDs), are

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable d ...

s that are commonly

spread Spread may refer to: Places * Spread, West Virginia Arts, entertainment, and media * ''Spread'' (film), a 2009 film. * ''$pread'', a quarterly magazine by and for sex workers * "Spread", a song by OutKast from their 2003 album ''Speakerboxxx/T ...

sexual activity Human sexual activity, human sexual practice or human sexual behaviour is the manner in which humans experience and express their sexuality. People engage in a variety of sexual acts, ranging from activities done alone (e.g., masturbation) ...

, especially

vaginal intercourse Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetrat ...

anal sex Anal sex or anal intercourse is generally the insertion and thrusting of the erect penis into a person's anus, or anus and rectum, for sexual pleasure.Sepages 270–271for anal sex information, anpage 118for information about the clitoris. O ...

and

oral sex Oral sex, sometimes referred to as oral intercourse, is sexual activity involving the stimulation of the genitalia of a person by another person using the mouth (including the lips, tongue, or teeth) and the throat. Cunnilingus is oral sex p ...

. The most prevalent STIs may be carried by a significant fraction of the human population.

References

{{DEFAULTSORT:Sexually transmitted infections by prevalence Sexually transmitted diseases and infections Infections with a predominantly sexual mode of transmission Papillomavirus Infectious disease-related lists