A vaginal yeast infection (vulvovaginal candidiasis) is a common fungal infection caused by an overgrowth of Candida, a type of yeast naturally present in the vagina. A yeast infection typically does not smell like fish. If you notice a strong, fishy odor, it is usually a sign of a different vaginal condition.
What Causes a Fishy Vaginal Odor?
The distinct, unpleasant fishy odor is most often caused by Bacterial Vaginosis (BV), an imbalance in the vaginal flora. BV results from an overgrowth of certain bacteria that displace the protective Lactobacilli. This microbial shift changes the vaginal environment, causing the characteristic smell.
The odor is caused by volatile compounds called amines, specifically trimethylamine (TMA), which is associated with the smell of spoiling fish. Bacteria convert odorless compounds into TMA, which becomes more noticeable when exposed to an alkaline environment, such as after sexual intercourse or during menstruation.
Another condition that can cause a foul odor is Trichomoniasis, a common sexually transmitted infection (STI) caused by the parasite Trichomonas vaginalis. The odor can be fishy or generally foul, often accompanied by a foamy, yellow-green discharge. Both BV and Trichomoniasis raise the vaginal pH level above the normal acidic range.
Recognizing the Signs of a Yeast Infection
A vaginal yeast infection is a fungal infection, and its symptoms are distinct from those that cause a fishy odor. The most noticeable symptom is typically intense itching and irritation in the vagina and vulva.
The discharge associated with a yeast infection is usually thick, white, and clumpy, often described as having a cottage cheese-like appearance. This discharge typically has little to no strong odor, unlike BV or Trichomoniasis. Some people report a mild, faintly sweet, or yeasty smell, similar to beer or bread.
Other common signs include a burning sensation during urination or sexual intercourse, and noticeable redness and swelling of the vulva. These symptoms are caused by the inflammatory response to the overgrowth of Candida.
Comparing Common Vaginal Infections
Differentiating between the three most common causes of abnormal vaginal symptoms—Yeast Infection, Bacterial Vaginosis (BV), and Trichomoniasis—is important because each requires a different treatment. Odor is often the simplest distinguishing factor: a Yeast Infection is typically odorless or mildly yeasty, while BV and Trichomoniasis present with a strong, unpleasant, or fishy odor. BV odor is distinctly fishy and may intensify after sex.
The color and consistency of the discharge also provide important clues. A Yeast Infection causes thick, white, and clumpy discharge. Conversely, BV usually produces a thin, grayish-white or off-white discharge. Trichomoniasis is often associated with a frothy, thin discharge that can range in color from yellow to greenish.
The main associated symptoms also vary. Intense itching and burning are the hallmarks of a Yeast Infection. BV may cause mild itching or no symptoms at all, aside from the odor. Trichomoniasis can cause general itching, burning, and soreness, sometimes accompanied by pain during urination. Both BV and Trichomoniasis cause the vaginal pH to rise above the normal acidic level of 3.8 to 4.5, while a Yeast Infection typically leaves the pH unchanged.
Diagnosis and Treatment
Given the overlap in symptoms, professional medical evaluation is necessary to confirm the exact cause of any abnormal vaginal symptoms. Self-diagnosing based on symptoms alone can be unreliable and may lead to using the wrong treatment, which can worsen the condition. A healthcare provider will typically perform a pelvic exam and may test the vaginal fluid for pH level, which quickly rules out a yeast infection if the pH is elevated.
A definitive diagnosis often involves microscopic examination of a fluid sample to look for characteristic yeast cells, specific bacteria, or the Trichomonas vaginalis parasite. Treatment is highly specific. A Yeast Infection is treated with antifungal medications (over-the-counter creams, suppositories, or prescription oral medication like fluconazole). In contrast, BV is treated with prescription antibiotics, such as metronidazole or clindamycin, to restore the bacterial balance. Trichomoniasis is treated with antiparasitic oral antibiotics like metronidazole or tinidazole.