Sexually transmitted diseases (STD), also referred to as sexually transmitted infections (STI) and venereal diseases (VD), are illnesses that have a significant probability of transmission between humans by means of sexual behavior, including vaginal intercourse, anal sex and oral sex. Some STIs can also be contracted by using IV drug needles after their use by an infected person, as well as through childbirth or breastfeeding.
Sexually transmitted infections have been well known for hundreds of years, and venereology is the branch of medicine that studies these diseases. While in the past, these illnesses have mostly been referred to as STDs or VD, in recent years the term sexually transmitted infections (STIs) has been preferred, as it has a broader range of meaning; a person may be infected, and may potentially infect others, without having a disease.
Human reproduction is any form of sexual reproduction resulting in the conception of a child, typically involving sexual intercourse between a man and a woman. During sexual intercourse, the interaction between the male and female reproductive systems results in fertilization of the woman's ovum by the man's sperm, which after a gestation period is followed by childbirth. The fertilization of the ovum may nowadays be achieved by artificial insemination methods, which do not involve sexual intercourse.
Bacterial vaginosis (BV) or very uncommonly vaginal bacteriosis is a disease of the vagina caused by bacteria. According to the U.S. Centers for Disease Control and Prevention (CDC), risk factors for BV include douching and having new or multiple sex partners, although it is unclear what role sexual activity plays in the development of BV. BV is caused by an imbalance of naturally occurring bacterial flora and is often confused with yeast infection (candidiasis) or infection with Trichomonas vaginalis (trichomoniasis), which are not caused by bacteria.
Pelvic inflammatory disease (or disorder) (PID) is a term for inflammation of the uterus, fallopian tubes, and/or ovaries as it progresses to scar formation with adhesions to nearby tissues and organs. This can lead to infertility. PID is a vague term and can refer to viral, fungal, parasitic, though most often bacterial infections. PID should be classified by affected organs, the stage of the infection, and the organism(s) causing it. Although a sexually transmitted infection (STI) is often the cause, many other routes are possible, including lymphatic, postpartum, postabortal (either miscarriage or abortion) or intrauterine device (IUD) related, and hematogenous spread. Two thirds of patients with laparoscopic evidence of previous PID were not aware they had PID.