Discharge that smells like eggs is almost always caused by an overgrowth of anaerobic bacteria in the vagina, most commonly a condition called bacterial vaginosis (BV). These bacteria produce sulfur-containing compounds and other chemicals that create that distinctive rotten or sulfurous egg smell. The good news: it’s treatable, and in some cases the smell has a harmless explanation tied to normal hormonal shifts.
Bacterial Vaginosis Is the Most Common Cause
Your vagina naturally contains a balance of bacteria, with beneficial species producing lactic acid to keep the environment slightly acidic (a healthy pH sits between 3.8 and 5.0). When that balance tips and anaerobic bacteria overgrow, the pH rises above 4.5 and those bacteria start producing chemicals like trimethylamine, putrescine, and cadaverine. These compounds are responsible for the strong, sulfurous or fishy smell many people describe as egg-like.
The primary bacterium behind BV is Gardnerella vaginalis. Along with the smell, you may notice thin, off-white, grayish, or greenish discharge. The odor often gets stronger after sex or during your period. BV isn’t a sexually transmitted infection, though sexual activity can trigger the bacterial shift. Other common triggers include douching, new soaps or body washes, and anything that disrupts the vagina’s natural acidity.
BV is extremely common. Many people with it have no symptoms beyond the odor, which is why a change in smell is often the first thing that gets noticed. It’s treated with a prescription vaginal gel or oral medication that clears the bacterial overgrowth, typically within five to ten days.
Hormonal Shifts Can Change Your Smell
Not every change in vaginal odor means something is wrong. Hormonal fluctuations throughout your menstrual cycle naturally alter the composition and volume of your discharge, and the smell can shift along with it. Around ovulation, for instance, discharge increases and may carry a slightly stronger or different scent than what you’re used to. The same applies during pregnancy, when higher estrogen levels increase blood flow to vaginal tissues and change the bacterial environment.
These hormonally driven changes are typically mild. If the smell is faint, comes and goes with your cycle, and isn’t accompanied by itching, burning, or unusual color, it’s likely normal variation rather than an infection.
Trichomoniasis and Other Infections
If the egg-like smell comes with yellow-green, frothy discharge plus itching or burning, trichomoniasis is a possibility. Trich is a sexually transmitted infection caused by a parasite. It pushes vaginal pH even higher than BV does, sometimes above 5.4, creating an environment where odor-producing organisms thrive. The CDC notes that trich discharge is often described as fishy-smelling and may be clear, white, yellowish, or greenish. Many people with trich also feel discomfort when urinating or notice genital redness and soreness.
Trich is treated with a prescription oral antibiotic, and sexual partners need treatment at the same time to prevent reinfection.
A Forgotten Tampon or Other Retained Object
This cause is more common than you might expect, and it produces one of the most intense sulfur or rotten-egg smells. When a tampon, menstrual disc, or other object stays in the vaginal canal too long, the warm, dark, moist environment becomes a breeding ground for bacteria. The Cleveland Clinic notes that this bacterial overgrowth can trigger BV on its own, compounding the odor problem.
Symptoms typically include a suddenly foul smell that worsens over days, unusual discharge, and sometimes pelvic pain or low-grade fever. If you suspect a retained object, a healthcare provider can remove it quickly and check for any resulting infection.
Menopause and Declining Estrogen
After menopause, declining estrogen levels thin the vaginal lining and reduce glycogen, the sugar that feeds protective lactobacilli bacteria. Without enough of these beneficial bacteria producing acid, the vaginal pH rises and other organisms can take over. This can lead to a condition called aerobic vaginitis, which is distinct from BV and produces a yellow discharge with a foul (but not fishy) odor that some people describe as sulfurous or egg-like.
Vaginal estrogen therapy can help restore the tissue and bacterial balance. If you’re postmenopausal and noticing a new or worsening smell, it’s worth mentioning at your next appointment since the underlying cause may differ from what’s typically seen in younger patients.
Signs That Point to Something More Serious
Pelvic inflammatory disease (PID) occurs when an infection, often from untreated BV or an STI, spreads from the vagina into the uterus or fallopian tubes. According to the CDC, PID can cause unusual discharge with a bad odor along with lower abdominal pain, fever, painful sex, burning during urination, and bleeding between periods. PID needs prompt treatment to prevent long-term complications like chronic pain or fertility problems.
In general, the Mayo Clinic recommends seeing a provider if you notice any of the following alongside the odor:
- Discharge color changes: greenish, yellowish, thick, or cottage cheese-like texture
- Persistent strong odor that doesn’t resolve on its own within a few days
- Itching, burning, or irritation of the vulva or vaginal opening
- Spotting or bleeding outside your normal period
- Fever or pelvic pain
What You Can Do Right Now
If the smell is new and mild, give it a day or two. Avoid douching, scented washes, or vaginal deodorants, all of which can worsen the bacterial imbalance causing the odor in the first place. Wear breathable cotton underwear and skip tight, non-breathable fabrics when possible.
If the smell persists beyond a few days, gets stronger, or arrives with any of the symptoms listed above, a healthcare provider can diagnose the cause with a simple exam and often a quick pH test or swab. Most causes of egg-smelling discharge clear up completely with a short course of treatment, and the odor resolves once the underlying bacterial imbalance is corrected.