HSV Transmission Risk Factors

What actually changes HSV-2 transmission risk between partners — with the trial figures behind each factor, and why no honest tool gives you one combined number.

Most people asking whether they can still have sex with herpes want one number. No study produces that number for your specific relationship — but several good trials do show which factors move risk, in which direction, and by how much.

Select what applies and you will get the actual trial findings for each, with the paper behind it.

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Is the partner who has HSV-2 taking daily suppressive antiviral therapy?

Are condoms used consistently?

Which direction is transmission being considered?

How often does the partner with HSV-2 get outbreaks?

How long ago was the partner with HSV-2 infected?

Nothing you select is sent anywhere — this runs entirely in your browser. This is not medical advice; treatment decisions belong with a clinician who knows your history.

The factor most people get wrong

If you assume that frequent outbreaks mean high transmission risk and no outbreaks mean low risk, the evidence does not support you.

In a trial of 1,484 monogamous serodiscordant couples, recurrence frequency before the study was essentially the same for source partners who transmitted HSV-2 and those who did not — 4.8 versus 5.1 recurrences per year. Among the 40 partners who transmitted, 8 of 27 in the placebo group had no recurrences at all during the study.

This matters practically: people frequently decide how careful to be based on whether they are currently having outbreaks. That instinct is not supported.

What each organisation publishes on its own page, checked 2026-08-12. A filled square means the page states it; an open square means it does not.

Why this tool refuses to give you a percentage

The figures behind each factor come from different study populations, follow-up periods, and definitions of transmission. One measured symptomatic acquisition over eight months; another measured per-act probability in African serodiscordant couples; another pooled prospective studies of condom users.

Multiplying them together would produce a precise-looking percentage that none of those studies supports. A calculator that gives you "your risk is 4.7%" is not measuring anything — it is combining incompatible numbers and presenting the result as a finding.

What you can take from this is directional and still useful: daily suppressive therapy has the largest single effect of anything trialled, condoms help meaningfully but partially, and outbreak frequency is not the signal people think it is.

What none of this covers

These trials studied heterosexual, monogamous, serodiscordant couples, mostly on HSV-2. They do not tell you about HSV-1 genital infection, non-monogamous arrangements, or same-sex couples, and they cannot tell you what will happen in your relationship specifically.

Decisions about suppressive therapy belong with a clinician who knows your history. This tool exists so that conversation starts from what the trials actually found rather than from a number someone made up.

For the fuller treatment of condom evidence specifically — including why the reduction is 30% rather than near-total — see condoms and herpes: what they protect and what they cannot cover.