Most sexually transmitted infections in men produce no obvious symptoms at all, which makes waiting for signs a unreliable strategy. Roughly 45% of gonorrhea cases and 77% of chlamydia cases never cause noticeable symptoms. The only definitive way to know if a man has an STD is through testing, but there are physical clues that can signal an infection when they do appear.
Discharge and Painful Urination
The most recognizable sign of a bacterial STI in men is unusual discharge from the penis. Gonorrhea typically produces a thick, yellowish-green discharge, while chlamydia tends to cause a thinner, clearer fluid. Both infections can also cause a burning sensation during urination. These symptoms usually develop within one to three weeks of exposure, though they can take longer.
A lesser-known infection called Mycoplasma genitalium can cause similar symptoms, including penile discharge and urinary discomfort. Like chlamydia, it often produces no symptoms at all. If discharge appears and a standard chlamydia and gonorrhea test comes back negative, this infection may be worth asking about.
Sores, Blisters, and Bumps
Genital sores are another major warning sign, but the type of sore matters. Syphilis produces what’s called a chancre: a single, firm, painless sore that appears about three weeks after exposure. Because it doesn’t hurt, many men don’t notice it or dismiss it as minor. Herpes, by contrast, causes clusters of small, painful blisters that break open and crust over. Both can appear on the penis, scrotum, or around the anus.
Genital warts from HPV look different from either. They appear as small, skin-colored bumps, sometimes with a cauliflower-like texture. They can grow on the tip or shaft of the penis, the scrotum, or around the anus, and they can also form in the mouth or throat after oral sex. Some warts are so small and flat they’re nearly invisible to the naked eye.
Rashes and Skin Changes
If syphilis goes untreated past its initial sore, it progresses to a second stage that produces a widespread rash. This rash is made up of round, brownish spots and can appear on the trunk, back, and limbs. The distinguishing feature is that it shows up on the palms of the hands and soles of the feet, which most other rashes don’t. It’s often subtle enough that people don’t notice it themselves. About 90% of people with secondary syphilis develop this rash.
In the genital area, secondary syphilis can also cause moist, flat growths that look similar to genital warts but are actually a different type of lesion entirely. These are painless and highly contagious.
Testicular Pain and Swelling
When bacterial STIs like chlamydia or gonorrhea go untreated, they can spread deeper into the reproductive tract and infect the epididymis, the coiled tube behind each testicle. This causes a swollen, tender, or warm scrotum, usually on one side. You might also notice pain during urination, pelvic discomfort, or discharge alongside the swelling.
If the infection becomes chronic (lasting longer than six weeks or recurring), it can lead to a fluid buildup around the testicle, an abscess, or in rare cases, reduced fertility. Testicular pain that develops gradually and won’t go away deserves prompt attention, especially if you’ve had unprotected sex recently.
Why Symptoms Alone Aren’t Enough
The core problem with relying on physical signs is that the most common STIs are specifically the ones least likely to produce them. Research estimates that 86% of untreated gonorrhea cases and 95% of untreated chlamydia cases remain untreated precisely because the person never develops symptoms. HIV can cause a brief flu-like illness a few weeks after infection, then remain silent for years. Hepatitis B can do the same. A man can carry and transmit multiple infections without ever feeling sick.
This is equally true of oral and anal infections. Chlamydia and gonorrhea in the throat or rectum rarely cause noticeable symptoms but are still transmissible. If you’ve had oral or anal sex, standard urine-based testing won’t catch infections at those sites. Throat and rectal swabs are needed separately.
What Testing Looks Like
STI testing for men is straightforward and usually involves two components: a urine sample and a blood draw. Urine tests detect chlamydia, gonorrhea, and trichomoniasis. Blood tests detect HIV, syphilis, hepatitis B, and sometimes herpes. No single test screens for everything, so you need to know which infections you’re being tested for.
Timing matters because every infection has a window period before tests become accurate:
- Gonorrhea: 5 days to 2 weeks after exposure
- Syphilis: about 4 weeks after exposure (1 to 2 weeks after a sore appears, and sores typically develop around 3 weeks post-exposure)
- HIV: 10 to 33 days for the most sensitive blood test, up to 90 days for a standard antibody test
Testing too early can produce a false negative. If you had a specific exposure you’re concerned about, testing at two weeks and again at three months gives you the most complete picture.
Who Should Get Tested and How Often
The CDC recommends that everyone between ages 13 and 64 get tested for HIV at least once, regardless of risk factors. Beyond that baseline, screening frequency depends on your situation.
Men who have sex with men should be tested for syphilis, chlamydia, and gonorrhea at least once a year, and for HIV at least annually as well. Those with multiple or anonymous partners benefit from testing every 3 to 6 months. Men who have sex only with women don’t have formal routine screening guidelines beyond the one-time HIV test, but testing after a new partner, a condom failure, or any symptoms is a practical approach.
If you’re noticing any combination of unusual discharge, genital sores, testicular pain, a rash on your palms or soles, or burning during urination, those are clear reasons to get tested. But the absence of all those signs doesn’t mean you’re in the clear. The most reliable way to know if a man has an STD is a lab test, not a visual check.