Most STIs have recognizable visual signs, but each one looks different, and many produce no visible symptoms at all. Knowing what to look for can help you understand what’s happening with your body, though visual identification alone is unreliable. One study found that a symptom-based approach correctly identified STIs only about 53% of the time, barely better than a coin flip. Lab testing is the only way to confirm an infection. That said, here’s what the most common STIs actually look like when they do show up.
Syphilis: Painless Sore, Then a Spreading Rash
Syphilis progresses through distinct stages, and each one looks different. In the first stage, a single sore called a chancre appears where the bacteria entered the body. It’s firm, round, small, and painless, which is part of what makes it easy to miss. The sore oozes fluid and typically shows up on the genitals, around the mouth, or near the anus. Because it doesn’t hurt, many people never notice it, and it heals on its own within a few weeks even without treatment.
If untreated, syphilis moves to its second stage, which produces a rash that can cover large areas of the body. The most distinctive feature is that this rash commonly appears on the palms of the hands and soles of the feet, which is unusual for most skin conditions and serves as a telling visual clue. The rash may also spread across the back, chest, and other areas. The lesions are generally flat or slightly raised and not itchy.
Genital Herpes: Blisters That Break Open
Herpes sores go through a predictable cycle. They start as small bumps or fluid-filled blisters around the genitals, anus, or mouth, appearing roughly 2 to 12 days after exposure. These blisters then rupture into painful open ulcers that ooze or bleed. Over the following days, scabs form and the sores gradually heal.
Before an outbreak, many people experience warning signs: tingling, itching, or shooting pain in the legs, hips, or buttocks. During an active outbreak, you may also notice painful urination or unusual discharge. Herpes is a recurring infection, so outbreaks can happen again, though they typically become less severe over time. Between outbreaks, the skin looks completely normal.
Genital Warts: Soft, Textured Growths
Genital warts caused by HPV appear as small, skin-colored or pink growths. They can show up on the labia, at the vaginal opening, on the penis shaft, or around and inside the anus. Their texture is what sets them apart from other bumps. Some are smooth and flat, but many have a rough, slightly raised surface sometimes compared to the top of a cauliflower. They can appear as a single bump or in clusters, and they’re generally painless.
Warts may take weeks or even months to appear after infection, so by the time you notice them, the exposure could have happened long ago. They range in size from barely visible to several millimeters across.
Molluscum Contagiosum: Dimpled Dome-Shaped Bumps
Molluscum bumps have a very specific look. They’re flesh-colored, dome-shaped, and typically 2 to 5 millimeters in diameter, roughly the size of a pencil eraser or smaller. The key identifying feature is a small dimple or indent in the center of each bump. This central depression is the hallmark that distinguishes molluscum from other skin conditions like warts or pimples. The bumps are firm, usually painless, and can appear in small clusters in the genital area, inner thighs, or lower abdomen.
Discharge Changes From Chlamydia, Gonorrhea, and Trichomoniasis
Some STIs don’t produce visible sores at all. Instead, they change the color, consistency, or smell of genital discharge. These changes can be subtle and overlap between infections, making it impossible to self-diagnose based on discharge alone.
Gonorrhea can cause cloudy white or yellowish discharge, though it frequently causes no symptoms whatsoever. Chlamydia may produce grayish or slightly discolored discharge, but again, it often stays silent. Trichomoniasis tends to be more noticeable: it’s strongly associated with yellow, sometimes frothy or purulent discharge accompanied by an abnormal vaginal odor and vulvar itching. In clinical exams, trichomoniasis can also cause visible redness and irritation of the vaginal and vulvar tissue.
In men, discharge from gonorrhea or chlamydia often appears as a white, yellow, or greenish drip from the urethra, sometimes accompanied by burning during urination.
Pubic Lice: Visible Insects and Eggs
Pubic lice (sometimes called crabs) are one of the few STIs you can actually see moving. Adult lice are tiny, about 1.5 to 2 millimeters long, tan to grayish-white, and flattened. They have six legs, and their two front legs are oversized and look like small pincher claws, which is where the “crabs” nickname comes from. You’ll find them clinging to coarse body hair, primarily in the pubic area.
Even if you don’t spot the lice themselves, you may notice their eggs (nits) attached firmly to individual hair shafts. Nits are oval, yellow to white, and don’t brush off easily. The most common symptom is intense itching, and you may also see tiny blue-gray spots on the skin from lice bites.
Why Many STIs Look Like Nothing at All
Perhaps the most important thing to understand is that the majority of STI cases produce no visible signs. In one study of men being regularly screened, all prevalent STIs at the start of the study were completely asymptomatic. Among new infections detected during follow-up, about 80% had no symptoms. For gonorrhea specifically, roughly 77% of new cases were asymptomatic. For chlamydia, about 84% showed no signs.
This is why visual self-checks, while useful, are not a substitute for testing. You can have an active, transmissible infection with completely normal-looking skin and no unusual discharge. If you’re concerned about a potential exposure, testing is the only reliable path to an answer, regardless of whether you see anything unusual.