Research has shown a link between trichomoniasis and two serious sequelae. Data suggest that:

- Trichomoniasis is associated with increased risk of transmission and infection of HIV.

- Trichomoniasis may cause a woman to deliver a low-birth-weight or premature infant.

- The role of trichomonas infection in causing cervical cancer is unclear, although trichomonas infection may be associated with co-infection with high-risk strains of HPV.

- "T. vaginalis" infection in males has been found to cause asymptomatic urethritis and prostatitis. In the prostate, it may create chronic inflammation that may eventually lead to prostate cancer.

There were about 58 million cases of trichomoniasis in 2013. It is more common in women (2.7%) than males (1.4%). It is the most common non-viral STI in the U.S., with an estimated 3.7 million prevalent cases and 1.1 million new cases per year. It is estimated that 3% of the general U.S. population is infected, and 7.5-32% of moderate-to-high risk (including incarcerated) populations.

Although previously considered a mere nuisance infection, untreated bacterial vaginosis may cause complications, such as increased susceptibility to sexually transmitted infections including HIV and pregnancy complications.

It has been shown that HIV-infected women with bacterial vaginosis (BV) are more likely to transmit HIV to their sexual partners than those without BV. Diagnostic criteria for BV have also been associated with a female genital tract factor that induces expression of HIV.

There is evidence of an association between BV and increased rates of sexually transmitted infections such as HIV/AIDS. BV is associated with up to a six-fold increase in HIV shedding. There is also a correlation between the absence of vaginal lactobacilli and infection by Neisseria gonorrhea and Chlamydia trachomatis. BV is a risk factor for viral shedding and herpes simplex virus type 2 infection. BV may increase the risk of infection with or reactivation of human papillomavirus (HPV).

In addition, bacterial vaginosis an intercurrent disease in pregnancy may increase the risk of pregnancy complications, most notably premature birth or miscarriage.

Pregnant women with BV have a higher risk of chorioamnionitis, miscarriage, preterm birth, premature rupture of membranes, and postpartum endometritis. BV is associated with gynecological and obstetric complications. Data suggest an association between BV, tubal factor infertility, and pelvic inflammatory disease. Women with BV who are treated with in vitro fertilization have a lower implantation rate and higher rates of early pregnancy loss.

Healthy vaginal microbiota consists of species which neither cause symptoms or infections, nor negatively affect pregnancy. It is dominated mainly by Lactobacillus species. BV is defined by the disequilibrium in the vaginal microbiota, with decline in the number of lactobacilli. While the infection involves a number of bacteria, it is believed that most infections start with Gardnerella vaginalis creating a biofilm, which allows other opportunistic bacteria to thrive.

One of the main risks for developing BV is douching, which alters the vaginal flora and predisposes women to developing BV. Douching is strongly discouraged by the U.S. Department of Health and Human Services and various medical authorities, for this and other reasons.

BV is a risk factor for pelvic inflammatory disease, HIV, sexually transmitted infections (STIs), and reproductive and obstetric disorders or negative outcomes. It is possible for sexually inactive persons to develop bacterial vaginosis.

Bacterial vaginosis may sometimes affect women after menopause. Also, subclinical iron deficiency may correlate with bacterial vaginosis in early pregnancy. A longitudinal study published in February 2006, in the "American Journal of Obstetrics and Gynecology", showed a link between psychosocial stress and bacterial vaginosis persisted even when other risk factors were taken into account. Exposure to the spermicide nonoxynol-9 does not affect the risk of developing bacterial vaginosis.

Having a female partner increases the risk of BV by 60%. The bacteria associated with BV have been isolated from male genitalia. BV microbiota has been found in the penis, coronal sulcus, and male urethra, in the male partners of infected females. Partners who have not been circumcised may act as a ‘reservoir’ increasing the likelihood of acquiring an infection after sexual intercourse. Another mode of transmission of the BV-associated microbiota is to a female sexual partner via skin-to-skin transfer. BV may be transmitted via the perineal enteric bacteria from the microbiota of the female and male genitalia.

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.

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.

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.

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 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"

The number of cases of vaginal yeast infection is not entirely clear because it is not a reportable disease and it is commonly diagnosed clinically without laboratory confirmation.

Candidiasis is one of the three most common vaginal infections along with bacterial vaginosis and trichomonas. Approximately 20% of women get an infection yearly. About 75% of women have at least one infection in their lifetime.

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

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.

A sexually transmitted infection present in a pregnant woman may be passed on to the infant before or after birth.

The risks and transmission probabilities of sexually transmitted diseases are summarized by act in the table:

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.

Urethritis is inflammation of the urethra. The most common symptom is painful or difficult urination. It is usually caused by infection with bacteria. The bacterial infection is often sexually transmitted, but not in every instance. Urethritis can be idiopathic.

Bacterial vaginosis (BV) is an infection caused by a change in the vaginal flora, which refers to the community of organisms that live in the vagina. It is the most common cause of pathological vaginal discharge in women of childbearing age and accounts for 40–50% of cases. In BV, the vagina experiences a decrease in a bacterium called lactobacilli, and a relative increase in a multitude of anaerobic bacteria with the most predominant being "Gardnerella vaginalis". This imbalance results in the characteristic vaginal discharge experienced by patients with BV. The discharge in BV has a characteristic strong fishy odor, which is caused by the relative increase in anaerobic bacteria.[1] The discharge is typically thin and grey, or occasionally green. It sometimes is accompanied by burning with urination. Itching is rare. The exact reasons for the disruption of vaginal flora leading to BV are not fully known. However, factors associated with BV include antibiotic use, unprotected sex, douching, and using an intrauterine device (IUD). The role of sex in BV is unknown, and BV is not considered an STI. The diagnosis of BV is made by a health care provider based on the appearance of the discharge, discharge pH > 4.5, presence of clue cells under the microscope, and a characteristic fishy odor when the discharge is placed on a slide and combined with potassium hydroxide ("whiff test"). The gold standard for diagnosis is a gram stain showing a relative lack of lactobacilli and a polymicrobial array of gram negative rods, gram variable rods, and cocci. BV may be treated with oral or intravaginal antibiotics, or oral or intravaginal lactobacillus.

Inflammation has many possible causes, including irritation by environmental substances, physical trauma, and infection such as bacterial, viral, or fungal. Some of these infections are sexually transmitted diseases.

It is less common among people who are circumcised as in many cases the foreskin contributes to the disease. Both not enough cleaning and too much cleaning can cause problems. Diabetes can make balanitis more likely, especially if the blood sugar is poorly controlled.

It is important to exclude other causes of similar symptoms such as penile cancer.

Hygiene, in particular the regular cleaning of the glans, is generally considered sufficient to prevent infection and inflammation of the foreskin. Full retraction of the foreskin may not be possible in boys younger than about ten years and some may not be able to fully retract their foreskin for cleaning until their late teens.

If contact dermatitis is suspected, soaps and other external irritants should be discontinued and a latex allergy should be investigated.

The treatment depends on identification of the cause. Irritants in the environment should be removed. Antibiotics and antifungals can be used to treat the infection, but good hygiene such as keeping the area dry is essential to stop recurrence, however excessive washing with soap can cause contact dermatitis.

If infection is sexually transmitted, sexual partners should be notified and treated.

Posthitis and balanitis (inflammation of the glans penis) usually occur together as balanoposthitis. Circumcision prevents balanoposthitis though balanitis can still occur separately.

Balanitis "is a common condition affecting 11% of adult men seen in urology clinics and 3% of children" in the United States; globally, balanitis "may occur in up to 3% of uncircumcised males".

Leukorrhea is also caused by trichomonads, a group of parasitic protozoan, specifically "Trichomonas vaginalis". Common symptoms of this disease are burning sensation, itching and discharge of frothy substance, thick, white or yellow mucous.

It is not a major issue but is to be resolved as soon as possible. It can be a natural defense mechanism that the vagina uses to maintain its chemical balance, as well as to preserve the flexibility of the vaginal tissue. The term "physiologic leukorrhea" is used to refer to leukorrhea due to estrogen stimulation.

Leukorrhea may occur normally during pregnancy. This is caused by increased bloodflow to the vagina due to increased estrogen. Female infants may have leukorrhea for a short time after birth due to their in-uterine exposure to estrogen.

The most acute complication is paraphimosis. In this condition, the glans is swollen and painful, and the foreskin is immobilized by the swelling in a partially retracted position. The proximal penis is flaccid. Some studies found phimosis to be a risk factor for urinary retention and carcinoma of the penis.

A number of medical reports of phimosis incidence have been published over the years. They vary widely because of the difficulties of distinguishing physiological phimosis (developmental nonretractility) from pathological phimosis, definitional differences, ascertainment problems, and the multiple additional influences on post-neonatal circumcision rates in cultures where most newborn males are circumcised. A commonly cited incidence statistic for pathological phimosis is 1% of uncircumcised males. When phimosis is simply equated with nonretractility of the foreskin after age 3 years, considerably higher incidence rates have been reported.

Others have described incidences in adolescents and adults as high as 50%, though it is likely that many cases of physiological phimosis or partial nonretractility were included.

Some intestinal parasitic infections may play a role in irritable bowel syndrome and other long-term sequelae.