The infection is usually spread from one person to another through vaginal, oral, or anal sex. Men have a 20% risk of getting the infection from a single act of vaginal intercourse with an infected woman. The risk for men that have sex with men (MSM) is higher. Active MSM may get a penile infection, while passive MSM may get anorectal gonorrhea. Women have a 60–80% risk of getting the infection from a single act of vaginal intercourse with an infected man. A pregnant women can pass on the infection to her unborn infant.

A mother may transmit gonorrhea to her newborn during childbirth; when affecting the infant's eyes, it is referred to as ophthalmia neonatorum. It may be able to spread through the objects contaminated with body fluid from an infected person. The bacteria typically does not survive long outside the body, typically dying within minutes to hours.

Chlamydia can be transmitted during vaginal, anal, or oral sex or direct contact with infected tissue such as conjunctiva. Chlamydia can also be passed from an infected mother to her baby during vaginal childbirth.

For sexually active women who are not pregnant, screening is recommended in those under 25 and others at risk of infection. Risk factors include a history of chlamydial or other sexually transmitted infection, new or multiple sexual partners, and inconsistent condom use. For pregnant women, guidelines vary: screening women with age or other risk factors is recommended by the U.S. Preventive Services Task Force (USPSTF) (which recommends screening women under 25) and the American Academy of Family Physicians (which recommends screening women aged 25 or younger). The American College of Obstetricians and Gynecologists recommends screening all at risk, while the Centers for Disease Control and Prevention recommend universal screening of pregnant women. The USPSTF acknowledges that in some communities there may be other risk factors for infection, such as ethnicity. Evidence-based recommendations for screening initiation, intervals and termination are currently not possible. For men, the USPSTF concludes evidence is currently insufficient to determine if regular screening of men for chlamydia is beneficial. They recommend regular screening of men who are at increased risk for HIV or syphilis infection.

In the United Kingdom the National Health Service (NHS) aims to:

1. Prevent and control chlamydia infection through early detection and treatment of asymptomatic infection;

2. Reduce onward transmission to sexual partners;

3. Prevent the consequences of untreated infection;

4. Test at least 25 percent of the sexually active under 25 population annually.

5. Retest after treatment.

Gonorrhea is caused by the bacterium "Neisseria gonorrhoeae". Previous infection does not confer immunity - a person who has been infected can become infected again by exposure to someone who is infected. Infected persons may be able to infect others repeatedly without having any signs or symptoms of their own.

Specific age groups, persons who participate in risky sexual behavior, or those have certain health conditions may require screening. The CDC recommends that sexually active women under the age of 25 and those over 25 at risk should be screened for chlamydia and gonorrhea yearly. Appropriate times for screening are during regular pelvic examinations and preconception evaluations. Nucleic acid amplification tests are the recommended method of diagnosis for gonorrhea and chlamydia. This can be done on either urine in both men and women, vaginal or cervical swabs in women, or urethral swabs in men. Screening can be performed:

- to assess the presence of infection and prevent tubal infertility in women

- during the initial evaluation before infertility treatment

- to identify HIV infection

- for men who have sex with men

- for those who may have been exposed to hepatitis C

- for HCV

Researchers had hoped that nonoxynol-9, a vaginal microbicide would help decrease STI risk. Trials, however, have found it ineffective and it may put women at a higher risk of HIV infection.

The most common bacterial cause of NGU is "Chlamydia trachomatis", but it can also be caused by "Ureaplasma urealyticum", "Haemophilus vaginalis", "Mycoplasma genitalium", Mycoplasma hominis, Gardnerella vaginalis, Acinetobacter lwoffi, Ac.calcoclaceticus and "E.coli".

Cervicitis can be caused by any of a number of infections, of which the most common are chlamydia and gonorrhea, with chlamydia accounting for approximately 40% of cases. As many half of pregnant women are asymptomatic with a gonorrhea infection of the cervix. "Trichomonas vaginalis" and herpes simplex are less common causes of cervicitis. There is a consistent association of M. genitalium infection and female reproductive tract syndromes. M. genitalium infection is significantly associated with increased risk of cervicitis.

Over one million cases of acute salpingitis are reported every year in the US, but the number of incidents is probably larger, due to incomplete and untimely reporting methods and that many cases are reported first when the illness has gone so far that it has developed chronic complications. For women age 16–25, salpingitis is the most common serious infection. It affects approximately 11% of females of reproductive age.

Salpingitis has a higher incidence among members of lower socioeconomic classes. However, this is thought of being an effect of earlier sex debut, multiple partners, and decreased ability to receive proper health care rather than any independent risk factor for salpingitis.

As an effect of an increased risk due to multiple partners, the prevalence of salpingitis is highest for people age 15–24 years. Decreased awareness of symptoms and less will to use contraceptives are also common in this group, raising the occurrence of salpingitis.

There are many causes of NGU. This is in part due to the large variety of organisms living in the urinary tract. "Ureaplasma urealyticum" and "Mycoplasma genitalium" are some of the culprits.

NGU is also associated with Reiter's syndrome,in which triad of Arthritis,Conjunctivitis & Urethritis is there.

The bacteria most associated with salpingitis are:

- N. gonorrhoeae

- Chlamydia trachomatis

- Mycoplasma

- Staphylococcus

- Streptococcus

However, salpingitis is usually polymicrobial, involving many kinds of organisms. Other examples of organisms involved are:

- Ureaplasma urealyticum

- Anaerobic and aerobic bacteria

Babies can also become infected by their mothers during birth. Some infectious agents may be transmitted to the embryo or fetus in the uterus, while passing through the birth canal, or even shortly after birth. The distinction is important because when transmission is primarily during or after birth, medical intervention can help prevent infections in the infant.

During birth, babies are exposed to maternal blood, body fluids, and to the maternal genital tract without the placental barrier intervening. Because of this, blood-borne microorganisms (hepatitis B, HIV), organisms associated with sexually transmitted disease (e.g., "Neisseria gonorrhoeae" and "Chlamydia trachomatis"), and normal fauna of the genitourinary tract (e.g., "Candida albicans") are among those commonly seen in infection of newborns.

Prognosis is highly variable. Spontaneous remission is common. Complete cure can be obtained with proper antibiotic treatments to kill the causative bacteria, such as tetracycline, doxycycline, or erythromycin. Prognosis is more favorable with early treatment. Bacterial superinfections may complicate course. Death can occur from bowel obstruction or perforation, and follicular conjunctivitis due to autoinoculation of infectious discharge can occur.

The embryo and fetus have little or no immune function. They depend on the immune function of their mother. Several pathogens can cross the placenta and cause (perinatal) infection. Often, microorganisms that produce minor illness in the mother are very dangerous for the developing embryo or fetus. This can result in spontaneous abortion or major developmental disorders. For many infections, the baby is more at risk at particular stages of pregnancy. Problems related to perinatal infection are not always directly noticeable.

The disease is classified as either gonococcal urethritis, caused by "Neisseria gonorrhoeae", or non-gonococcal urethritis (NGU), most commonly caused by "Chlamydia trachomatis". NGU, sometimes called nonspecific urethritis (NSU), has both infectious and noninfectious causes.

Urethritis is part of triad of Reiter's Syndrome.

Other causes include:

- Adenoviridae

- Uropathogenic "Escherichia coli" (UPEC)

- Herpes simplex

- Cytomegalovirus

- "Mycoplasma genitalium"

- Reactive arthritis

- "Trichomonas vaginalis"

- "Ureaplasma urealyticum"

- "Methicillin-resistant Staphylococcus aureus"

- "Group B streptococcus"

Cervices is inflammation of the uterine cervix. Cervicitis in women has many features in common with urethritis in men and many cases are caused by sexually transmitted infections. Death may occur. Non-infectious causes of cervicitis can include intrauterine devices, contraceptive diaphragms, and allergic reactions to spermicides or latex condoms.

The condition is often confused with vaginismus which is a much simpler condition and easily rectified with simple exercises.

Lymphogranuloma venereum (LGV) (also known as "Climatic bubo", "Durand–Nicolas–Favre disease", "Poradenitis inguinale", and "Strumous bubo") is a sexually transmitted disease caused by the invasive serovars L1, L2, L2a or L3 of "Chlamydia trachomatis".

LGV is primarily an infection of lymphatics and lymph nodes. "Chlamydia trachomatis" is the bacterium responsible for LGV. It gains entrance through breaks in the skin, or it can cross the epithelial cell layer of mucous membranes. The organism travels from the site of inoculation down the lymphatic channels to multiply within mononuclear phagocytes of the lymph nodes it passes.

In developed nations, it was considered rare before 2003. However, a recent outbreak in the Netherlands among gay men has led to an increase of LGV in Europe and the United States. A majority of these patients are HIV co-infected.

LGV was first described by Wallace in 1833 and again by Durand, Nicolas, and Favre in 1913. Since the 2004 Dutch outbreak many additional cases have been reported, leading to greater surveillance. Soon after the initial Dutch report, national and international health authorities launched warning initiatives and multiple LGV cases were identified in several more European countries (Belgium, France, the UK, Germany, Sweden, Italy and Switzerland) and the US and Canada. All cases reported in Amsterdam and France and a considerable percentage of LGV infections in the UK and Germany were caused by a newly discovered Chlamydia variant, L2b, a.k.a. the Amsterdam variant. The L2b variant could be traced back and was isolated from anal swabs of men who have sex with men (MSM) who visited the STI city clinic of San Francisco in 1981. This finding suggests that the recent LGV outbreak among MSM in industrialised countries is a slowly evolving epidemic. The L2b serovar has also been identified in Australia.

Vulvovaginitis in children may be "nonspecific", or caused by irritation with no known infectious cause, or infectious, caused by a pathogenic organism. Nonspecific vulvovaginitis may be triggered by fecal contamination, sexual abuse, chronic diseases, foreign bodies, nonestrogenized epithelium, chemical irritants, eczema, seborrhea, or immunodeficiency. It is treated with topical steroids; antibiotics may be given in cases where itching has resulted in a secondary infection.

Infectious vulvovaginitis can be caused by group A beta-hemolytic "Streptococcus" (7-20% of cases), "Haemophilus influenzae, Streptococcus pneumoniae, Staphylococcus aureus, Shigella, Yersinia", or common STI organisms ("Neisseria gonorrhoeae, Chlamydia trachomatis, Trichomonas vaginalis", herpes simplex virus, and human papillomavirus)"." Symptoms and treatment of infectious vulvovaginitis vary depending on the organism causing it. "Shigella" infections of the reproductive tract usually coexist with infectious of the gastrointestinal tract and cause mucous, purulent discharge. They are treated with trimethoprim-sulfamethoxazole. "Streptococcus" infections cause similar symptoms to nonspecific vulvovaginitis and are treated with amoxicillin. STI-associated vulvovaginitis may be caused by sexual abuse or vertical transmission, and are treated and diagnosed like adult infections.

Vaginitis is the disruption of the healthy vaginal microbiota. The vaginal microbiota consists of those organisms which generally do not cause symptoms, infections, and results in good pregnancy outcomes, and is dominated mainly by Lactobacillus species. The disruption of the normal microbiota can cause a vaginal yeast infection. Vaginal yeast infection can affect women of all ages and is very common. The yeast "Candida albicans" is the most common cause of vaginitis. Specific forms of vaginal inflammation include the following types:

Infectious vaginitis accounts for 90% of all cases in reproductive age women:

- Candidiasis: vaginitis caused by proliferation of "Candida albicans", "Candida tropicalis", "Candida krusei"

- Bacterial vaginosis: vaginitis caused by increased growth of "Gardnerella" (a bacterium).

- Aerobic vaginitis

Other less common infections are caused by gonorrhea, chlamydia, "Mycoplasma", herpes, "Campylobacter", improper hygiene, and some parasites, notably "Trichomonas vaginalis". Women who have diabetes develop infectious vaginitis more often than women who do not.

Vaginal infections often have multiple causes (varies between countries between 20 and 40% of vaginal infections), which present challenging cases for treatment. Indeed, when only one cause is treated, the other pathogens can become resistant to treatment and induce relapses and recurrences. Therefore, the key factor is to get a precise diagnosis and treat with broad spectrum anti-infective agents (often also inducing adverse effects).

Further, either a change in pH balance or introduction of foreign bacteria in the vagina can lead to infectious vaginitis. Physical factors that have been claimed to contribute to the development of infections include the following: constantly wet vulva due to tight clothing, chemicals coming in contact with the vagina via scented tampons, antibiotics, birth control pills, or a diet favoring refined sugar and yeast.

Sexually transmitted disease that affect the vagina include:

- Herpes genitalis. The herpes simplex virus (HSV) can infect the vulva, vagina, and cervix, and this may result in small, painful, recurring blisters and ulcers. It is also common for there to be an absence of any noticeable symptoms.

- Gonorrhea

- Chlamydia

- Trichomoniasis

- Human papillomavirus (HPV), which may cause genital warts.

HIV/AIDS can be contracted through the vagina during vaginal intercourse, but it is not associated with any local vaginal or vulval disease.

Because of STIs, health authorities and other health outlets recommend safe sex practices when engaging in sexual activity.

Regular testing for sexually transmitted infections is encouraged for prevention. The risk of contracting pelvic inflammatory disease can be reduced by the following:

- Using barrier methods such as condoms; see human sexual behavior for other listings.

- Seeking medical attention if you are experiencing symptoms of PID.

- Using hormonal combined contraceptive pills also helps in reducing the chances of PID by thickening the cervical mucosal plug & hence preventing the ascent of causative organisms from the lower genital tract.

- Seeking medical attention after learning that a current or former sex partner has, or might have had a sexually transmitted infection.

- Getting a STI history from your current partner and strongly encouraging they be tested and treated before intercourse.

- Diligence in avoiding vaginal activity, particularly intercourse, after the end of a pregnancy (delivery, miscarriage, or abortion) or certain gynecological procedures, to ensure that the cervix closes.

- Reducing the number of sexual partners.

- Sexual monogamy.

- Abstinence

While infections may occur without sex, a high frequency of intercourse increases the risk. Personal hygiene methods or tight-fitting clothing, such as tights and thong underwear, do not appear to increase the risk.

The disease incidence varies widely depending on the geographical location. The most extensive epidemiological survey on this subject has been carried out by Dharmasena et al. who analysed the number of neonates who developed neonatal conjunctivitis in England from 2000 to 2011. In addition to the incidence of this sight threatening infection they also investigated the time trends of the disease. According to them the incidence of Neonatal conjunctivitis (Ophthalmia Neonatorum) in England was 257 (95% confidence interval: 245 to 269) per 100,000 in 2011.

A vaginal yeast infection results from overgrowth of candida albicans, or yeast, in the vagina. This is a relatively common infection, with over 75% of women having experienced at least one yeast infection at some point in their life. Risk factors for yeast infections include recent antibiotic use, diabetes, immunosuppression, increased estrogen levels, and use of certain contraceptive devices including intrauterine devices, diaphragms, or sponges. It is not a sexually transmitted infection. Candida vaginal infections are common; an estimated 75% of women will have at least one yeast infection in their lifetime. Vaginal discharge is not always present in yeast infections, but when occurring it is typically odorless, thick, white, and clumpy. Vaginal itching is the most common symptom of candida vulvovaginitis. Women may also experience burning, soreness, irritation, pain during urination, or pain during sex. The diagnosis of Candida vulvovaginitis is made by looking at a sample taken from the vagina under the microscope that shows hyphae (yeast), or from a culture. It is important to note that the symptoms described above may be present in other vaginal infections, so microscopic diagnosis or culture is needed to confirm the diagnosis. Treatment is with intra-vaginal or oral anti-fungal medications.

In pregnancy, higher levels of estrogen make a woman more likely to develop a yeast infection. During pregnancy, the "Candida" fungus is more common, and recurrent infection is also more likely. There is tentative evidence that treatment of asymptomatic candidal vulvovaginitis in pregnancy reduces the risk of preterm birth.