Testicular or scrotal pain is most often not an STI, but two bacterial infections, chlamydia and gonorrhea, can cause it by inflaming the tube behind the testicle (epididymitis). The same pain can also mean testicular torsion, a surgical emergency. Sudden, severe pain needs the ER today. A dull, gradual ache plus discharge points toward an STI you should get tested for.
Chlamydia trachomatis
Neisseria gonorrhoeae
| Item | Value |
|---|---|
| Chlamydia | curable — Chlamydia trachomatis |
| Gonorrhea | curable — Neisseria gonorrhoeae |
The short list of likely causes
When the scrotum hurts or swells, clinicians sort the causes into a few buckets. The STI-related ones are chlamydia and gonorrhea, which can travel up the genital tract and inflame the epididymis. The non-STI causes include testicular torsion (a twisted spermatic cord that cuts off blood flow), direct injury, and a hydrocele (a painless fluid collection around the testicle). These overlap so much by feel that you rule out the emergency first, then test for an infection.
Which STIs cause testicular or scrotal pain
In sexually active men, the usual STI mechanism is the same: bacteria reach the urethra, then ascend the vas deferens to the epididymis, the coiled tube behind each testicle that stores and matures sperm. Inflammation there (epididymitis) produces a one-sided ache and swelling that builds over hours to days, often with urinary symptoms or discharge. Left untreated, that inflammation can scar the tube and threaten fertility, so a quick diagnosis matters even when the pain feels manageable.
Chlamydia
Chlamydia, caused by the bacterium Chlamydia trachomatis, is the most common STI cause of epididymitis in younger men chlamydia. It's a famously quiet infection, and about half of infected men notice nothing at all CDC chlamydia. When symptoms do appear, they usually show up within one to three weeks of exposure and may include burning on urination or discharge before any testicular pain develops. The classic pattern is a gradual, one-sided scrotal ache in a young, sexually active man, building slowly rather than hitting all at once like torsion.
Gonorrhea
Gonorrhea, caused by Neisseria gonorrhoeae, can infect the genitals, rectum, and throat, and it's the second classic STI cause of epididymitis gonorrhea. In men it more often announces itself: burning on urination and a white, yellow, or green penile discharge, with swollen or painful testicles showing up less commonly CDC gonorrhea. When the testicle is involved, the discharge is the clue that pushes a clinician toward gonorrhea, or a chlamydia co-infection, since the two travel together.
When it's not an STI
Plenty of scrotal pain has nothing to do with sex. The one that can't wait is testicular torsion, where the spermatic cord twists and chokes off the testicle's blood supply. It strikes suddenly, often severely, sometimes waking someone from sleep, and the testicle can sit high or look oddly angled. Torsion is a surgical emergency, and the window to save the testicle is measured in hours. A clinician rules this out before anything else.
Other common non-STI causes are far less urgent. A direct injury, a kick or a sports collision, produces pain and bruising tied to a clear event. A hydrocele is a soft, usually painless collection of fluid around the testicle that makes the scrotum feel heavy or full rather than acutely sore. Neither needs STI treatment, but neither should be assumed without an exam.
How to tell them apart
You often can't tell them apart by feel alone. Torsion and STI epididymitis both cause one-sided pain and swelling, and chlamydia in particular is frequently silent. A test is what settles which one it is, if any. A few features help a clinician lean one way:
- Speed of onset — sudden, severe pain over minutes suggests torsion; a gradual ache over hours to days fits infection.
- Age — torsion skews toward teens and young adults; STI epididymitis appears in sexually active men of any age.
- Associated symptoms — burning urination or penile discharge points toward chlamydia or gonorrhea; nausea and a high-riding testicle point toward torsion.
- Trigger — a clear blow or accident points to injury; a painless, slowly enlarging scrotum suggests a hydrocele.
Any single clue can mislead, and they overlap. You usually can't self-diagnose this, and a test turns a guess into an answer.
Side-by-side comparison
| Cause | Onset | Key clues | STI? | Urgency |
|---|---|---|---|---|
| Testicular torsion | Sudden, minutes | Severe pain, high-riding or twisted testicle, nausea | No | Emergency — ER now |
| Chlamydia (epididymitis) | Gradual, hours–days | One-sided ache; often silent or mild urinary symptoms | Yes | Test & treat soon |
| Gonorrhea (epididymitis) | Gradual, hours–days | Penile discharge, burning urination, swollen testicle | Yes | Test & treat soon |
| Injury | Immediate, after trauma | Clear event, bruising | No | Seen if severe |
| Hydrocele | Slow, weeks–months | Painless, soft, heavy fullness | No | Routine evaluation |
How it's tested
For the STI side, a nucleic acid amplification test (NAAT) is the preferred method for both chlamydia and gonorrhea, with gonorrhea NAATs running high sensitivity and specificity CDC STI Guidelines, 2021. In practice that usually means a urine sample, a self-collected swab, or a quick exam depending on what's suspected, often free or low-cost at health departments, Planned Parenthood, and Title X clinics, with results back in a few days. You can get tested, and if your exposure was recent, check when to test after exposure so you don't test too early to be reliable.
What to do next
If torsion is even a possibility, meaning sudden, severe, one-sided pain, skip testing and go to an emergency room immediately. If the pain is gradual and you have discharge or burning, get an STI test and start treatment promptly. Both chlamydia and gonorrhea are curable with prescribed antibiotics, and any recent partners should be treated too. Don't wait out the pain hoping it passes, because untreated epididymitis can scar the tube and affect fertility.
Red flags — when to get seen urgently
- Sudden, severe testicular pain, especially if it woke you from sleep or peaked within minutes.
- A testicle that sits higher than usual, looks twisted, or has changed shape.
- Pain with nausea, vomiting, fever, or feeling generally unwell.
- Rapidly worsening swelling, redness, or warmth of the scrotum.
- Any scrotal pain after a significant injury that isn't easing.
When in doubt about torsion, treat it as an emergency. The testicle's blood supply is on a clock, and it's far better to be checked and reassured than to lose the window.