Yes, you can have syphilis and herpes at the same time. In fact, co-infection is common enough that the CDC specifically notes more than one cause can be present in any genital ulcer. In one study of HIV-positive men who have sex with men, nearly 23% had both herpes and syphilis simultaneously. Having both infections at once creates a more complicated clinical picture and raises the risk of transmitting or acquiring other STIs, including HIV.
Why Co-infection Happens
Syphilis and herpes spread through similar routes: direct skin-to-skin or mucous membrane contact during sexual activity. If you’re exposed to both pathogens around the same time, or if you already carry one and later encounter the other, there’s nothing about either infection that prevents the second from taking hold. Herpes is especially common as a background infection because it’s lifelong once acquired, and many people don’t know they have it. So a person with dormant herpes can contract syphilis at any point, and the reverse is also true.
The two infections operate through entirely different mechanisms. Syphilis is caused by a bacterium, while herpes is caused by a virus. They don’t compete with each other, and treatment for one does nothing against the other.
How the Sores Differ
One reason co-infection gets missed is that both infections cause sores in the genital, anal, or oral area. But the sores look and feel quite different when they appear on their own.
- Syphilis chancre: Typically a single, firm, round sore with clean edges. It’s painless, which is why many people ignore it or don’t notice it at all. It appears 10 to 90 days after exposure, with an average of about 21 days.
- Herpes lesions: Usually multiple small blisters that cluster together, break open, and form shallow, painful ulcers. A first outbreak typically shows up 2 to 12 days after exposure, though some people don’t develop visible symptoms for months or even years.
The tricky part is when both are present at the same time. A syphilis sore can become painful if it’s also infected with herpes, or herpes blisters can mask the firmer chancre underneath. In one study that tested ulcers from patients with suspected syphilis, about 21% of the samples also contained herpes virus, and roughly 5% showed true co-infection in the same lesion. This means that what looks like a straightforward case of one infection may actually involve both.
How Both Infections Are Diagnosed
When you show up with any genital, anal, or perianal ulcer, CDC guidelines recommend testing for both syphilis and herpes as part of the standard workup. That evaluation typically includes syphilis blood tests (and, if available, a nucleic acid test from the sore itself), plus a herpes culture or nucleic acid test from the lesion and a type-specific herpes blood test.
Some clinics now use a multiplex PCR test that can detect syphilis bacteria, herpes type 1, and herpes type 2 from a single swab of the ulcer. In clinical studies, this test identified syphilis bacteria with about 80% sensitivity and nearly 99% specificity. The advantage is speed and convenience: one swab screens for multiple causes at once, rather than running separate tests for each infection. HIV testing is also recommended for anyone with a genital ulcer who doesn’t already know their status.
Treatment for Both at Once
The good news is that treating both infections simultaneously is straightforward because the treatments don’t interfere with each other. Syphilis in its early stages is treated with a single injection of a long-acting antibiotic. Once treated, the bacterial infection is cured. Herpes, on the other hand, is managed with antiviral pills taken for 7 to 10 days during a first outbreak, and the medication works best when started as early as possible.
Because timing matters for both infections, CDC guidelines recommend starting treatment at the first visit if either infection is suspected, even before lab results come back. Delaying syphilis treatment increases the chance of spreading it to partners, and delaying herpes treatment reduces the medication’s effectiveness at shortening the outbreak.
After initial treatment, syphilis is gone (assuming follow-up testing confirms the cure), but herpes stays in the body permanently. People with herpes may take daily antiviral medication to suppress future outbreaks and reduce the risk of transmission.
The Combined Risk for HIV
Having either syphilis or herpes increases your vulnerability to HIV, but having both at the same time compounds that risk substantially. Open ulcers from either infection create a direct path for HIV to enter the bloodstream. Earlier estimates suggested that genital ulcers roughly doubled to quintupled the per-act risk of HIV transmission. But a critical review of the evidence found those numbers were heavily diluted by including sexual encounters where no ulcer was actually present at the time. When researchers isolated only the acts where an ulcer was active, the risk jumped dramatically, with some studies finding a 10- to 100-fold increase in HIV transmission probability.
For uncircumcised men with active genital ulcers, one study calculated that the chance of acquiring HIV from a single sexual act with an infected partner was as high as 43%. That figure drops significantly with circumcision and condom use, but it illustrates how powerfully open sores amplify HIV risk. This is one of the main reasons prompt treatment of both syphilis and herpes matters beyond just resolving symptoms.
Who Is Most at Risk for Co-infection
Certain factors make co-infection more likely. In the study from China, age was the strongest predictor: people between 25 and 50 were about 4.5 times more likely to have both infections than those under 25, and people over 50 were 43 times more likely. This likely reflects cumulative sexual exposure over time. People who began sexual activity at a younger age (18 or under) also had roughly 2.5 times the odds of co-infection.
More broadly, anyone with one STI is at higher risk for others. The same sexual encounters that expose you to herpes can expose you to syphilis, and the biological disruption caused by one infection (inflammation, open sores, immune activation in genital tissue) makes it easier for a second infection to establish itself. Regular STI screening, particularly if you have new or multiple partners, catches co-infections that might otherwise go unnoticed, especially since both syphilis chancres and herpes outbreaks can appear in hard-to-see locations or cause minimal symptoms.