What causes a foul, fishy odor below?

Under normal circumstances, the term "below" refers to the vagina. A fishy or foul odor from the vagina may be associated with factors such as menstrual cycle changes, sexual activity, bacterial vaginosis, trichomoniasis, vulvovaginal candidiasis, and others. It is recommended to seek medical attention promptly, identify the underlying cause, and receive symptomatic treatment under the guidance of a healthcare professional. Specific analyses are as follows:

1. Menstrual Cycle Changes

During a woman's menstrual cycle, hormonal fluctuations may disrupt the balance of vaginal flora, leading to a decrease in lactobacilli and allowing other bacteria to proliferate, which may result in vaginal odor or a fishy smell. Maintaining good personal hygiene, using mild cleansing products, and wearing breathable cotton underwear can help support vaginal health.

2. Sexual Activity

During sexual intercourse, friction and mixing of secretions may temporarily alter the pH level of the vagina, disrupting the microbial environment and potentially causing transient vaginal odor. Paying special attention to hygiene before and after sexual activity, and ensuring both partners maintain good personal hygiene habits, can help protect reproductive health and prevent potential discomfort or infections.

3. Bacterial Vaginosis

Bacterial vaginosis is primarily caused by an imbalance of vaginal bacteria. This dysbiosis leads to a significant reduction in beneficial bacteria while harmful bacteria multiply excessively, disrupting the natural acidic environment of the vagina and resulting in abnormal, fishy-smelling discharge. Symptoms may also include increased vaginal discharge with changes in color and consistency. Treatment may include medications such as metronidazole tablets, lactobacillus vaginal capsules, or clindamycin hydrochloride cream, as prescribed by a physician.

4. Trichomoniasis (Trichomonas Vaginitis)

Trichomoniasis is mainly caused by infection with *Trichomonas vaginalis*. This pathogen consumes glycogen in the vagina, damaging the mucosal lining and triggering an inflammatory response, ultimately leading to a strong fishy or unpleasant odor. Other symptoms may include itching, burning, and pain. Treatment under medical supervision may involve medications such as Guansong compound antipruritic wash solution, tinidazole tablets, or fluconazole capsules.

5. Vulvovaginal Candidiasis

Vulvovaginal candidiasis is primarily caused by excessive growth of fungi such as *Candida*. When *Candida* multiplies rapidly, it may damage the vaginal mucosa, leading to an unusual odor that may resemble a fishy smell. Common accompanying symptoms include thick, white, cheese-like discharge, itching, and burning pain. Treatment may include antifungal medications such as itraconazole capsules, terbinafine hydrochloride tablets, or Honghe Fuyin Wash Solution, as directed by a healthcare provider.

Maintaining regular sleep patterns, practicing good personal hygiene—especially keeping the vulvar area clean and dry—and avoiding over-cleaning to prevent disruption of the natural vaginal flora balance can effectively help prevent vaginal infections.