An unusual or persistent change in genital odor often raises concern about health, particularly regarding the possibility of a Sexually Transmitted Infection. A healthy genital area typically possesses a mild, natural scent that can vary based on diet, activity, or hormonal cycles. An odor that becomes distinctly strong, unpleasant, or fishy, especially when accompanied by other physical changes, often signals an imbalance in the natural microbial environment.
Specific Infections That Cause Odor
The most distinct and commonly recognized foul odor, often described as fishy, is associated with the parasite-caused STI, Trichomoniasis (Trichomonas vaginalis). When symptomatic, it frequently produces a frothy, yellow-green discharge in those with a vagina, alongside the strong odor.
A more frequent cause of the characteristic fishy odor, however, is Bacterial Vaginosis (BV), an infection that is sexually associated but not strictly an STI. BV involves an overgrowth of anaerobic bacteria that naturally exist in the genital tract, disrupting the normal balance of protective Lactobacilli. This condition is the most common cause of abnormal genital odor and discharge, which is typically thin and grayish-white.
Other bacterial STIs, such as Chlamydia and Gonorrhea, may occasionally be linked to a foul-smelling discharge. This discharge can range in color from yellow to greenish and signals an infection that requires medical attention. Unlike the infections that cause the fishy smell, common viral infections like Human Papillomavirus (HPV) or Herpes Simplex Virus (HSV) do not typically cause a direct change in odor.
How Certain Infections Create Smell
The specific, strong “fishy” odor associated with both Bacterial Vaginosis and Trichomoniasis is directly related to the metabolic waste products of the overgrowing microorganisms. These infections thrive when the usual acidity of the genital tract is neutralized or disrupted, allowing anaerobic bacteria to flourish. The overgrowth leads to the production of chemical compounds known as volatile amines.
The primary volatile amine responsible for the strong, unpleasant scent is trimethylamine. This compound is the same substance that gives decaying fish their characteristic smell. The odor is often reported to intensify after sexual intercourse, as semen is naturally alkaline and can temporarily increase the pH level, further liberating the amines.
Other Common Causes of Genital Odor
Not all changes in odor are due to STIs or sexually-associated infections, and many common factors can alter the natural scent. Simple poor hygiene can lead to a musty or sour milk smell as sweat, dead skin cells, and oil accumulate and interact with surface bacteria. Since the genital area contains many sweat glands, high activity or tight, non-breathable clothing can also lead to a musky odor.
Changes in diet can also impact scent, as highly aromatic foods like garlic, onions, asparagus, or strong spices may cause a temporary change in body secretions. Hormonal fluctuations related to the menstrual cycle, pregnancy, or menopause can shift the pH balance of the environment, leading to a temporary change in odor. During menstruation, the presence of blood, which contains iron, can cause a temporary metallic or coppery smell.
Another cause of a sudden, extremely foul or “rotten” odor is a forgotten foreign object, most often a retained tampon. This creates an ideal environment for bacteria to multiply, leading to a putrid smell. While a yeast infection is a common cause of discharge, it typically produces a sweet, bread-like, or yeasty odor and is not usually the source of a strong, foul smell.
When to Seek Testing and Treatment
Any new, persistent, or noticeably strong genital odor warrants an evaluation by a healthcare provider, especially if it is accompanied by other symptoms. Signs that require professional attention include an odor combined with abnormal discharge, burning, itching, or pain. Self-diagnosis is unreliable, and a medical professional can perform tests to accurately distinguish between an STI, Bacterial Vaginosis, a yeast infection, or another underlying issue.
Diagnosis often involves a physical exam and testing a sample of discharge to determine the precise cause, such as identifying the presence of Trichomonas vaginalis or the overgrowth of anaerobic bacteria. Treatment protocols vary depending on the diagnosis, but infections like Bacterial Vaginosis and Trichomoniasis are typically treated with prescription antibiotics or antiparasitic medications. If an STI is diagnosed, sexual partners must also be tested and treated to prevent reinfection and minimize the risk of complications.