Rectal bleeding can come from several sexually transmitted infections — most often gonorrhea, chlamydia, herpes, and syphilis when they infect the anus or rectum and cause proctitis (inflammation of the rectal lining). But the most common causes of blood aren't STIs at all: hemorrhoids and anal fissures. Because these overlap, a test settles which one it is.
discharge and burning; can also hit throat/rectum
often silent; discharge or burning if anything
painful blisters that crust over; tends to recur
a single painless sore (chancre); later a body rash
| Item | Value |
|---|---|
| Gonorrhea | curable — discharge and burning; can also hit throat/rectum |
| Chlamydia | curable — often silent; discharge or burning if anything |
| Genital herpes | managed — painful blisters that crust over; tends to recur |
| Syphilis | curable — a single painless sore (chancre); later a body rash |
Which STIs can cause rectal bleeding?
When an STI causes rectal bleeding, the mechanism is usually proctitis. The bacterium or virus inflames and irritates the rectal mucosa until it weeps blood, mucus, or pus. Bleeding from an STI tends to be small-volume, often mixed with discharge, and frequently comes with pain, urgency, or the feeling of needing to pass stool when there's nothing there (tenesmus). Rectal infection follows receptive anal contact, but some people have no idea where the exposure happened, so guessing fails. Here's how each candidate tends to behave.
Gonorrhea
Gonorrhea is caused by the bacterium Neisseria gonorrhoeae, which can infect the genitals, rectum, and throat CDC. In the rectum it's a classic cause of proctitis — anal itching, discharge, soreness, painful bowel movements, and bleeding or blood-streaked stool. Many rectal infections are silent, so bleeding may be the first thing you notice. The same organism produces the better-known genital signs: in men, burning on urination and a white, yellow, or green penile discharge; in women, often nothing, or painful urination, more vaginal discharge, and bleeding between periods. A gonorrhea test uses a NAAT, the preferred screening method, with high sensitivity and specificity CDC.
Chlamydia
Chlamydia, caused by Chlamydia trachomatis, is the quiet partner to gonorrhea and behaves much the same way in the rectum CDC. It's a notoriously silent infection — roughly three quarters of infected women and half of infected men have no symptoms at all. When rectal chlamydia does speak up, it's proctitis: discharge, pain, and bleeding. A separate, more aggressive form (the LGV serovars) causes severe ulcerative proctitis with significant bleeding and pain, and is more common among men who have sex with men. If you've been treated before, watch for chlamydia reinfection, because repeat infection is common and easy to miss.
Genital herpes
Genital herpes, caused by HSV-1 and HSV-2, produces blisters that break into painful sores CDC. When those lesions land in or around the anus and rectum, the raw, broken skin can bleed, especially during a bowel movement. The first outbreak is usually the worst: clustered blisters, deep soreness, and sometimes flu-like fever, body aches, and swollen glands; sores can take a week or more to heal. Herpes proctitis tends to cause severe pain out of proportion to what you can see, plus tenesmus. Most people, though, have no or very mild symptoms and never get diagnosed. Recurrences are shorter and milder, often warned of by a tingling prodrome. If outbreaks are frequent, ask about suppressive therapy and other alternative herpes treatments.
Syphilis
Syphilis, caused by Treponema pallidum, opens with a primary chancre — one or more painless, firm, round sores at the site of infection, which can be the anus or rectum CDC. A rectal chancre may bleed a little and is easy to mistake for a fissure or hemorrhoid because it doesn't hurt. The chancre appears about three weeks after exposure (the range runs ten to ninety days) and then heals on its own, which fools people into thinking the problem's gone. If untreated, the secondary stage follows with a rough red or reddish-brown rash that can appear on the palms and soles, mucous-membrane lesions, fever, swollen lymph nodes, patchy hair loss, and fatigue. Syphilis is curable with antibiotics, and screening matters especially during pregnancy — see syphilis in pregnancy.
When rectal bleeding is NOT an STI
Most rectal bleeding has nothing to do with sex. Hemorrhoids and anal fissures are far more common causes CDC, 2021. Bleeding always deserves evaluation, so don't assume it's "just a hemorrhoid" without checking.
- Hemorrhoids — swollen blood vessels in or around the anus that bleed bright red, usually painlessly, with strain or hard stool.
- Anal fissures — small tears in the anal lining that cause sharp pain during a bowel movement followed by bright-red blood on the paper.
- Diet, constipation, and straining — hard stools that scrape or tear the canal.
- Inflammatory bowel disease — Crohn's or ulcerative colitis, which inflame the gut and cause blood mixed with diarrhea.
- Polyps or, less often, colorectal cancer — which is why new or persistent bleeding in older adults always gets worked up.
- Diverticular disease — small pouches in the colon wall that can bleed.
How to tell them apart
You usually can't tell by looking. These conditions overlap too much by sight, and several STIs are frequently silent, so the symptom alone won't tell you which one (if any) it is. A few patterns nudge the odds: bright-red blood only on the paper with sharp wiping pain leans toward a fissure; painless bleeding with itching leans toward hemorrhoids; bleeding mixed with mucus or pus, urgency, and tenesmus leans toward STI proctitis; a painless firm sore that bleeds and then vanishes raises syphilis; exquisitely painful grouped ulcers raise herpes. These are clues, not verdicts. Because the symptoms overlap, you can't self-diagnose this; a test turns a guess into an answer.
| Cause | Typical bleeding pattern | Pain | Other tells |
|---|---|---|---|
| Hemorrhoids | Bright red, on paper/in bowl | Usually painless | Itching, lump, strain-related |
| Anal fissure | Bright red streak with stool | Sharp, during/after BM | Hard stool, visible tear |
| Gonorrhea / chlamydia proctitis | Blood streaked, with discharge | Aching, urgency | Mucus/pus, tenesmus, often silent |
| Herpes proctitis | Oozing from broken sores | Severe | Blisters/ulcers, prodrome, flu-like first time |
| Syphilis (primary) | Light from a chancre | Painless | Firm round sore that self-heals |
How it's tested
Testing depends on what's suspected: a urine sample, a self-collected or clinician-collected rectal swab for gonorrhea and chlamydia NAAT, a swab of any visible sore for herpes by NAAT or culture CDC, and two blood tests for syphilis — a nontreponemal test (RPR or VDRL) plus a treponemal test (TP-PA, FTA-ABS, EIA, or CIA) CDC, 2024. If proctitis is suspected, the clinician may look directly at the rectal lining. Testing is often free or low-cost at health departments, Planned Parenthood, and Title X clinics, with results usually back in a few days — here's how to get tested, and the when to test after exposure guide explains timing so you don't test too early.
What to do next
Get evaluated rather than waiting it out. If a test confirms an STI, gonorrhea, chlamydia, and syphilis are cured with antibiotics, and herpes is managed with antivirals. Treat any partners and finish the full course; for the specific regimens and follow-up, see the treatment guidance for each infection CDC. If the cause turns out to be a fissure or hemorrhoid, simple measures — fiber, fluids, not straining — usually fix it.
Red flags — get seen urgently
- Heavy or persistent bleeding, large clots, or blood that won't stop.
- Black, tarry, or maroon stool, which suggests bleeding higher up the GI tract.
- Dizziness, fainting, racing heart, or a drop in blood pressure.
- Severe rectal or abdominal pain, high fever, or chills.
- Unintentional weight loss, a change in bowel habits, or a family history of colorectal cancer.
- Any rectal bleeding that's new for you, recurrent, or unexplained always warrants evaluation.