Nonpathological vaginal discharge ranges in pH from 3.8 to 4.2 and is typically white or clear in color, though it can be yellowish. Nothing is visible under a microscope in a vaginal wet mount and treatment with KOH (potassium hydroxide) does not give off an odor, which could indicate pathology. It is produced by cervical and vaginal glands. Vaginal discharge is neccessary for vaginal lubrication during sexual intercourse and also it proccess of the body's normal cleansing. 

While most discharge is normal and can reflect the various stages of the menstrual cycle, some discharge can be a result of an infection. One typical example of physiological (e.g. in pregnancy) and also patological type of vaginal discharge is leukorrhea.

Leukorrhea is a thick, whitish or yellowish vaginal discharge. There are many causes of leukorrhea, the usual one being estrogen imbalance. The amount of discharge may increase due to vaginal infection or sexually transmitted diseases (STDs), and also it may disappear and reappear from time to time, this discharge can keep occurring for years in which case it becomes more yellow and foul-smelling; it is usually a non-pathological symptom secondary to inflammatory conditions of vagina or cervix. Leukorrhea may occur normally during pregnancy. This is caused by increased blood flow 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.

Patological vaginal discharge is an extremely distressful condition for a woman, which can result from a variety of physiological states as well as pathological conditions. Early detection of pathological vaginal discharge is important to prevent complications of underlying diseases which can severely compromise women’s health, fertility and survival.

Changes in vaginal discharge can caused by pathological causes such as genital tract malignancy, fistulae, STDs infection, especially chlamydia and gonorrhea, vaginosis and pelvic inflammatory diseases.

Cancer

Vaginal discharge can be presented in uterine cancer and fallopian tube cancer. Primary fallopian tube carcinoma can be detected in early stage if detected the symptoms such as watery vaginal discharge and vaginal bleeding.

Fistula

Vesicovaginal fistula is an abnormal fistulous tract extending between the bladder (or vesico) and the vagina that allows the continuous involuntary discharge of urine into the vagina and then out of it. 

STDs 

Chlamydia is a sexually transmitted infection caused by the bacterium Chlamydia trachomatis. In women, symptoms may include abnormal vaginal discharge which can be yellow or milky white, burning during urination, and bleeding in between periods, although most women do not experience any symptoms.

Gonorrhea is caused by bacterium that lives on moist mucous membranes in the urethra, vagina, rectum, mouth, throat, and eyes. The infection can spread through contact with the penis, vagina, mouth or anus. Symptoms of Gonorrhea usually appear 2 to 5 days after contact with an infected partner however, some men might not notice symptoms for up to a month. Symptoms in women may include vaginal discharge which may be thin or watery and green or yellow, burning or itching while urinating, painful sexual intercourse, severe pain in lower abdomen (if infection spreads to fallopian tubes), or fever (if infection spreads to fallopian tubes), however many women do not show any symptoms.

Vaginosis

Bacterial vaginosis (BV) (Pic. 1) is the most common genital tract infection in women during their reproductive years and it has been associated with serious health complications, such as preterm delivery and acquisition or transmission of several sexually transmitted agents. BV is characterized by a reduction of beneficial lactobacilli and a significant increase in number of anaerobic bacteria (a common cause of infections). Among genital infections, bacterial vaginosis (BV) is the leading vaginal disorder in women of childbearing age, contributing to more than 60% of all vulvovaginal infections. BV, as a whole, has been associated with serious health problems, including pre-term birth and spontaneous abortion. Clinically, a profuse vaginal discharge and a rotten fish vaginal odor are characteristic symptoms, although some women with BV remain asymptomatic.

Pelvic inflammatory diseases

Inflammatory disease is usually the result of infection ascending from the endocervix causing endometritis (inflammation of the endometrium, the inner lining of the uterus), salpingitis (infection and inflammation in the fallopian tubes), parametritis (an inflammation of the connective tissue adjacent to the uterus), oophoritis (an inflammation of the ovary), tuboovarian abcess and/or pelvic peritonitis. The presentation is abnormal vaginal discharge or cervical discharge which is often purulent.

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Sources

Sexually transmitted infection ―sourced from Wikipedia licensed under CC BY-SA 3.0
Vaginal discharge ―sourced from Wikipedia licensed under CC BY-SA 3.0
Pelvic Inflammatory Disease ―sourced from Wikidot licensed under CC BY- SA 3.0
Vesicovaginal fistula ―sourced from Wikipedia licensed under CC BY- SA 3.0
Leukorrhea ―sourced from Wikipedia licensed under CC BY- SA 3.0
Vaginal discharge ―by Häggström licensed under CC0
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