I slept with someone who has herpes. Do I have it?

What one night does and does not mean

Start with the only comfort that is actually true: most exposures do not transmit. In the classic prospective study of 144 heterosexual couples in which one partner had genital HSV-2 and the other did not, 14 couples transmitted over a median of 334 days of ordinary couple life, which is 9.7% across roughly a year of repeated exposure, not one night. Direction mattered: transmission happened in 16.9% of couples where the positive partner was the man and 3.8% where it was the woman.

None of that converts to a personal percentage for your particular night, and this site does not invent one. What it does tell you is that a single condomless encounter with someone who has herpes is a reason to test on schedule, not a verdict.

If symptoms show up

A first outbreak, when one happens, tends to announce itself: clustered blisters or open sores where contact happened, sometimes with fever and swollen glands. If that appears, do not wait for any 12-week mark. Go in while the sore is fresh and ask for a swab test (NAAT, or culture where that is all that is offered). CDC's guidelines note that The sensitivity of viral culture is low, especially for recurrent lesions, and decreases rapidly as lesions begin to heal, which is the clinical way of saying: a healing sore stops giving answers. A positive swab can also be typed, and knowing HSV-1 versus HSV-2 changes what your future likely looks like, as our over-time guide explains.

One more honest note: many first infections cause nothing you would notice. In the largest prospective cohort, 2,393 initially HSV-2-negative adults, 155 acquired HSV-2 and only 37% of those infections were recognized symptomatically. The other 63% were found by blood test alone. No symptoms by week two is good news about your week, not an all-clear.

The 12-week rule

Blood tests look for antibodies, not the virus, and CDC's guidelines state that Both type-specific and type-common antibodies to HSV develop during the first weeks after infection and persist indefinitely. Early on there is simply nothing for the test to find. The same page says the sensitivity of type-specific HSV-2 tests runs 80% to 98% and that false-negative results might be more frequent at early stages of infection. The operative instruction, quoted exactly: in cases of recent suspected HSV-2 acquisition, repeat type-specific antibody testing 12 weeks after the presumed time of acquisition is indicated.

Practically, that means: no symptoms, no test this week. Put a date 12 weeks out in your calendar, request a type-specific IgG test then, and spend the interval not spiraling. If waiting without information feels unbearable, an earlier negative can be repeated at 12 weeks, but only the later result settles the question.

Reading the result

A clearly positive HSV-2 IgG is an answer. A barely positive one often is not: the most commonly used test is, in CDC's words, often falsely positive at low index values of 1.1 to 3.0. One study CDC cites put the test's overall specificity at 57.4%, and at 39.8% for those low-index results, which means a low-positive is wrong more often than it is right. If your number sits in that band, ask about confirmatory testing before you absorb the result as fact.

And test for the right thing. A positive HSV-1 result alone cannot tell you it came from that night: nearly half of American adults carry HSV-1, most since childhood cold-sore age. Our kissing guide covers why that number is so ordinary.

Talking to them, not at them

If they told you beforehand, they did the hard, honest thing, and the fair follow-ups are logistical: which type, whether they take daily medication, when their last outbreak was. If you found out afterward, say what you know and ask the same questions before assigning intent; plenty of people genuinely did not know, because 63% of infections in that cohort went unrecognized. The dating-someone guide has the fair-questions script, written for the person on your side of the conversation.

If it comes back positive

Then you join roughly 520 million people aged 15 to 49 worldwide with HSV-2, most of whom date, partner, and live ordinary lives, and the practical playbook is short: a typed diagnosis, a conversation with a clinician about daily antivirals, and honesty with partners going forward. The after-diagnosis guide covers the first weeks; first disclosure covers the telling. The fear you are feeling this week is the same fear someone once felt about telling you, which is worth remembering whichever way your result lands.