Bleeding between periods can be an early sign of a sexually transmitted infection, most often chlamydia or gonorrhea, which inflame the cervix and make it bleed easily, especially after sex. But spotting also has common non-STI causes like hormonal birth control, fibroids, polyps, and ovulation. Because these overlap, a test is what tells you which it is.
Chlamydia trachomatis
Neisseria gonorrhoeae
| Item | Value |
|---|---|
| Chlamydia | curable — Chlamydia trachomatis |
| Gonorrhea | curable — Neisseria gonorrhoeae |
Which STIs cause bleeding between periods?
Often the cause is cervicitis, inflammation of the cervix, the lower part of the uterus that opens into the vagina. When a bacterial infection irritates the cervical tissue, that surface becomes fragile and friable and bleeds at the slightest contact. So this kind of bleeding often shows up after intercourse (postcoital bleeding) or as light spotting between periods (intermenstrual bleeding) rather than as a heavy flow. Two STIs are the usual culprits.
Chlamydia
Chlamydia is caused by the bacterium Chlamydia trachomatis, with most US genital infections coming from serovars D–K CDC chlamydia fact sheet. It's a 'silent' infection: roughly three quarters of infected women and half of infected men have no symptoms at all. When symptoms do appear, they usually surface within one to three weeks after exposure. In women, the early signs are abnormal vaginal discharge and burning on urination; bleeding between periods tends to show up as the infection spreads upward, often alongside lower abdominal or low-back pain, fever, and pain during intercourse. That spotting is worth taking seriously, because if you're noticing it more than once you may also be dealing with a repeat or persistent infection. See why chlamydia reinfection is so common and why retesting matters.
Gonorrhea
Gonorrhea is caused by Neisseria gonorrhoeae, a bacterium that can infect the genitals, rectum, and throat CDC, About Gonorrhea. Like chlamydia, it's frequently silent in women, and most have no symptoms. When symptoms do occur, they include painful or burning urination, increased vaginal discharge, and bleeding between periods. In men the picture is different: burning on urination and a white, yellow, or green penile discharge, with swollen or painful testicles less commonly. The cervical inflammation it produces mirrors chlamydia almost exactly, so the bleeding pattern alone won't separate the two; you need a lab result. Here's how a gonorrhea test works and what the results mean.
When it's not an STI
Plenty of bleeding between periods has nothing to do with an infection. The most common non-STI explanations include:
- Hormonal contraception — the pill, patch, ring, implant, or hormonal IUD often cause breakthrough spotting, especially in the first few months or if doses are missed.
- Uterine fibroids — benign muscular growths in the wall of the uterus that can cause spotting and heavier or longer periods.
- Cervical or endometrial polyps — small, usually non-cancerous tissue growths that bleed easily, much like an inflamed cervix does.
- Ovulation spotting — a small, brief drop in estrogen mid-cycle can release a little blood, typically light and short-lived.
None of these are sexually transmitted, but several produce the same light, off-schedule bleeding an STI does, which is the whole problem.
How to tell them apart
You usually can't, by symptom alone. The causes overlap too much to distinguish by sight, and several, chlamydia and gonorrhea included, are frequently silent, so the bleeding may be your only clue. A clinician weighs context rather than appearance. Recent new or untreated partners and accompanying discharge or pelvic pain push toward an STI. A recent change in birth control points to hormonal breakthrough bleeding. Predictable mid-cycle timing suggests ovulation, and bleeding tied to heavier, longer periods raises the question of fibroids or polyps. Even then, those are starting hypotheses, and a test is what turns a guess into an answer.
Side-by-side comparison
| Cause | Typical bleeding pattern | Other clues | How it's confirmed |
|---|---|---|---|
| Chlamydia | Spotting between periods, often after sex; appears as infection spreads | Often none; possible discharge, burning urination, pelvic pain | NAAT (urine or swab) |
| Gonorrhea | Bleeding between periods; can be after sex | Often none; possible discharge, painful urination | NAAT (urine or swab) |
| Hormonal contraception | Breakthrough spotting, often early or with missed doses | Recent start/change of method | Clinical history; rule out infection |
| Fibroids / polyps | Spotting plus heavier or longer periods | Pelvic pressure or fullness | Pelvic exam, ultrasound |
| Ovulation spotting | Light, brief, predictably mid-cycle | Tied to fertile window | Cycle tracking; exam |
How it's tested
For both chlamydia and gonorrhea, the nucleic acid amplification test (NAAT) is the preferred method. It detects the bacteria's genetic material and is highly accurate, with gonorrhea NAAT sensitivity usually above 90% and specificity around 99% CDC STI Treatment Guidelines, 2021. In practice that means a urine sample, a self-collected vaginal swab, or a quick exam, depending on what's suspected. Testing is free or low-cost at health departments, Planned Parenthood, and Title X clinics, and results usually come back within a few days. You can get tested for the full how-to, and if the bleeding followed a recent encounter, check when to test after exposure so you don't test too early to catch it.
What to do next
If a test confirms chlamydia or gonorrhea, both are bacterial and curable with antibiotics, and partners need treatment too so you don't get reinfected. Don't try to match symptoms to a regimen on your own. The specific drugs and follow-up timing depend on the infection and the site, so let a clinician direct treatment and any retesting. If the cause turns out to be hormonal or structural, the fix is different again, so confirming the cause comes first.
Red flags — when to get seen urgently
Some bleeding warrants same-day or emergency care rather than a routine appointment. Get seen promptly if you have:
- Heavy bleeding that soaks through a pad an hour, or passing large clots.
- Bleeding with fever, severe lower abdominal or pelvic pain, which can signal pelvic inflammatory disease (infection that has spread to the uterus and tubes and threatens fertility).
- Feeling faint, dizzy, or short of breath alongside the bleeding.
- Any bleeding during a known or possible pregnancy.
- Bleeding after sex that keeps recurring, since it should always be evaluated rather than ignored.