Vaginitis Basics: How Yeast Infection, Bacterial Vaginosis and Trichomoniasis Differ

Vaginal itching, discharge, odor, or burning usually comes from one of three causes: a yeast infection, bacterial vaginosis (BV), or trichomoniasis. These three conditions can look and feel a lot alike, which is exactly the problem. According to the CDC’s STI treatment guidelines, most women will have a vaginal infection at some point in their life, and getting a history from a patient alone has been shown to be an unreliable way to figure out which one it is.

That’s why guessing and self-treating with the wrong product can leave the real cause untreated. This guide breaks down how these three conditions differ, what testing actually involves, and when symptoms need prompt attention.

When to Seek Care Sooner Rather Than Later

Most vaginal symptoms are not an emergency, but a few situations call for prompt medical attention rather than waiting:

• You are pregnant and have any new vaginal symptoms, discharge, or odor.
• You have pelvic or lower abdominal pain along with vaginal discharge.
• You have a fever along with vaginal symptoms.
• Symptoms are severe, rapidly worsening, or you’ve never had similar symptoms diagnosed before.
• Symptoms don’t improve, or come back, after using an over-the-counter product.

This article does not diagnose or treat anything. It’s here to help you understand why testing matters and what a clinician visit for vaginal symptoms typically involves.

Why You Can’t Reliably Self-Diagnose by Symptoms

Itching, discharge, and odor overlap so much across these three conditions that CDC guidance specifically warns that history alone can lead to the wrong. A careful exam plus lab testing is considered the reliable way to sort out the cause. Testing commonly includes checking the vaginal pH, examining a sample under a microscope, and, increasingly, a nucleic acid amplification test (NAAT), which is more sensitive than older methods for detecting trichomoniasis and some yeast infections.

ACOG notes that to get accurate test results, it’s best to avoid vaginal medications, douching, sex, or spermicides for a few days before a visit for vaginal symptoms.

How the Three Common Causes Compare

Yeast Infection (Vulvovaginal Candidiasis)

• What it is: An overgrowth of Candida, a yeast that’s normally present in the vagina in small amounts.
• Is it an STI? Generally not considered sexually transmitted, though it’s discussed alongside STIs because it’s often diagnosed in people being evaluated for one.
• Typical pattern: Associated with a normal vaginal pH, unlike BV or trichomoniasis.
• Testing: A sample of discharge examined under a microscope, or a culture, can confirm the diagnosis.

Bacterial Vaginosis (BV)

• What it is: A shift in the normal vaginal bacteria, where protective bacteria are replaced by an overgrowth of other bacteria. CDC identifies BV as the most common cause of vaginal discharge worldwide.
• Is it an STI? Not classified as an STI, but it’s linked to sexual activity — CDC notes women who have never been sexually active are rarely affected, and new or multiple partners and douching are associated with higher risk.
• Typical pattern: A thin, milk-like discharge and a fishy odor, especially noticeable after sex. CDC also reports that most women with BV have no symptoms at all, which is part of why testing (not symptom-guessing) matters.
• Testing: Clinicians look for a combination of signs, including discharge appearance, vaginal pH, odor, and cells seen under a microscope.

Trichomoniasis

• What it is: An infection caused by a parasite, Trichomonas vaginalis.
• Is it an STI? Yes — CDC identifies it as the most prevalent nonviral STI worldwide, estimated to.
• Typical pattern: The large majority of people with trichomoniasis have minimal or no symptoms, so someone can carry and pass it on without knowing. When symptoms do occur, discharge may be more noticeable, sometimes with an unusual color or odor.
• Testing: A NAAT is the most sensitive way to detect it; older microscopy methods can miss a meaningful number of cases.

A Simple Checklist Before You Guess

• Have I had this exact combination of symptoms diagnosed by a clinician before, or is this new?
• Am I pregnant, or could I be?
• Do I have pain, fever, or symptoms that are getting worse quickly?
• Have I tried an over-the-counter product already without improvement?
• Do I have a new or additional sex partner I should mention at a visit?

If you answered yes to any of these, that’s a signal to get tested rather than to self-treat based on a guess.

Vaginitis and Pregnancy

Vaginal infections deserve extra attention during pregnancy. CDC guidance notes that symptomatic BV in pregnancy has been associated with, and trichomoniasis in pregnancy has been associated with preterm delivery and. Because of this, pregnant women with symptoms are generally tested and evaluated promptly rather than waiting. This is a conversation to have directly with a prenatal care provider — see our Pregnancy & Preconception guide for more on what prenatal visits typically cover.

Extra Caution: HIV and Recurrent Symptoms

CDC notes that BV appears to recur more often in women with HIV infection, and routine annual trichomoniasis screening is recommended for women with HIV. If you’re managing HIV or another condition that affects your immune system, or if symptoms keep coming back, that’s worth raising directly with your clinician rather than working through it with over-the-counter products alone.

Frequently Asked Questions

Can I tell which infection I have just from my symptoms?

Not reliably. CDC guidance is direct about this: taking a history alone isn’t enough to accurately identify the cause of vaginal symptoms, and guessing can lead to using the wrong treatment. Testing is the only way to know for sure.

Is a yeast infection an STI?

Generally, no. Yeast infections aren’t classified as sexually transmitted infections, though they’re often discussed alongside STIs because people with vaginal symptoms are frequently evaluated for both at the same time.

Can I just use an over-the-counter yeast infection product without getting tested first?

This is a decision to make with a clinician, especially if it’s your first time having these symptoms, if you’re pregnant, or if a past over-the-counter treatment didn’t work. Since symptoms overlap so much between these conditions, treating for the wrong one means the actual cause goes unaddressed.

If I have trichomoniasis, does my partner need treatment too?

Partner treatment is part of how trichomoniasis is managed, since reinfection from an untreated partner is common. This is something a clinician will walk you through directly as part of your care plan.

Limits of This Information

• This article explains general differences between three common causes of vaginal symptoms. It does not cover every possible cause — conditions like cervicitis or noninfectious irritation can also cause similar symptoms.
• It does not diagnose your symptoms, recommend a treatment, or tell you whether to start, stop, or change any medication.
• Testing methods, availability, and turnaround time vary by clinic and lab and aren’t addressed here.

Educational Disclaimer

This article is for general educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Vaginal symptoms can have several different causes that look similar to each other, and only testing by a qualified clinician can determine which one applies to you. Always consult a qualified health care provider about new, persistent, severe, or recurring vaginal symptoms, and seek prompt care if you are pregnant or have fever or pelvic pain along with your symptoms. See our full Medical Disclaimer. For a broader look at routine reproductive health visits, see Reproductive Health & Preventive Care, and for more on STI screening in general, see our STI & Sexual Health guide.