LIFELONG VIRAL INFECTION / CARE & TRANSMISSION
HSV-1 and HSV-2
Herpes is common and manageable. Either HSV type can infect oral or genital tissue, although their recurrence patterns differ. Infection may transmit without a visible sore. Antiviral medication, avoiding contact during symptoms and barriers reduce risk; a diagnosis does not establish when it was acquired. [34]
Transmission risk
HSV-1: risk by type of contact
Bottom line. HSV-1 is a recognized kissing and oral-sex infection as well as a cause of genital herpes. There is no reliable percentage per kiss or oral act, and HSV-2 transmission figures should not be substituted.
General
Oral
Vaginal
Anal
Kissing
What changes the risk (3)
- Active lesions and source site. LOW for an exact multiplier: active oral sores are an important exposure condition; asymptomatic shedding also matters. No validated lesion-versus-no-lesion per-act multiplier. Sources 1
- Genital recurrence and shedding. MEDIUM: genital HSV-1 generally recurs and sheds less often than genital HSV-2; this does not supply a conversion factor between the two viruses. Sources 2
- Suppressive treatment. LOW for transmission effect: antiviral treatment can manage disease, but the HSV-2 transmission-reduction trial cannot establish an HSV-1 prevention percentage. CDC notes no data establishing prevention of genital HSV-1 transmission with suppressive therapy. Sources 2
Condoms and dental dams
No validated HSV-1-specific condom or dental-dam effect size. Partial protection is inferred from lesion coverage; HSV-2 efficacy figures are not interchangeable. Evidence: Low Sources 2, 1
HSV-2: risk by type of contact
Bottom line. Condoms and suppressive antivirals reduce HSV-2 transmission but do not eliminate uncovered-skin exposure. The available per-act numbers come from a particular heterosexual cohort and should not be generalized to every couple or route.
General
Oral
Vaginal
Anal
Kissing
What changes the risk (4)
- Suppressive valacyclovir. MEDIUM for one transmission RCT: overall acquisition over 8 months was 1.9% with treatment versus 3.6% with placebo; HR 0.52 (95% CI 0.27-0.99). Couples were immunocompetent and heterosexual; counseling and condoms were offered in both arms. This is not a condomless annual risk. Sources 6
- Condom study disagreement. MEDIUM: Magaret estimated 96% reduction male-to-female (95% CI 84-99) and 65% female-to-male (-5 to 88); the latter interval includes no benefit. Martin pooled prospective studies found HR 0.70 (0.40-0.94). Populations and endpoints differ; do not average. Sources 5, 3
- Circumcision. MEDIUM: Ugandan randomized-trial adjusted HR 0.72 (95% CI 0.56-0.92) for male HSV-2 acquisition; not protection for receptive partners or every population. Sources 7
- Symptoms and asymptomatic shedding. LOW for exact multipliers: active lesions/prodrome and time since infection affect shedding, but symptom-free contact is not a measured zero-risk state. Sources 1
Condoms and dental dams
Six prospective datasets support partial protection (pooled HR 0.70). One HIV-coinfected-source cohort fitted per-act efficacy of 96% male-to-female and 65% female-to-male, with substantial uncertainty. No anal/oral/dam-specific numerical efficacy established. Evidence: Medium Sources 3, 5
Sources for this risk profile (7)
- CDC CDC, 2021. Genital Herpes - STI Treatment Guidelines. cdc.gov
- WHO WHO fact sheet, 2025. Herpes simplex virus. who.int
- Martin ET et al. Archives of Internal Medicine, 2009. A pooled analysis of the effect of condoms in preventing HSV-2 acquisition. DOI: 10.1001/archinternmed.2009.177. pmc.ncbi.nlm.nih.gov
- CDC CDC, 2024. About STI Risk and Oral Sex. cdc.gov
- Magaret AS et al. Clinical Infectious Diseases, 2016. Effect of Condom Use on Per-act HSV-2 Transmission Risk in HIV-1, HSV-2-discordant Couples. DOI: 10.1093/cid/civ908. pmc.ncbi.nlm.nih.gov
- Corey L et al. New England Journal of Medicine, 2004. Once-daily valacyclovir to reduce the risk of transmission of genital herpes. DOI: 10.1056/NEJMoa035144. nejm.org
- Tobian AAR et al. New England Journal of Medicine, 2009. Male circumcision for the prevention of HSV-2 and HPV infections and syphilis. DOI: 10.1056/NEJMoa0802556. pubmed.ncbi.nlm.nih.gov
* How to read these figures. Each is a published estimate under the conditions shown beside it, usually an untreated partner and a single act or partnership. It is not a prediction of your personal risk.
- Evidence: High
- Several prospective studies or a systematic review broadly agree.
- Evidence: Medium
- One or two studies, wide uncertainty, or a model.
- Evidence: Low
- Guideline judgment, case reports, or extrapolation.
Where no risk level is shown, the evidence cannot rank it. That is not the same as low.
Evidence reviewed through 2026-10-27. For reference only; not medical advice.
HSV-1: when to test after a possible exposure
Swab a fresh suspicious lesion promptly; there is no validated universal post-exposure blood-test date that rules out oral or genital HSV-1.
When to be seen sooner. A new sore is best swabbed while it is fresh, rather than waiting weeks for an antibody test.
-
HSV PCR / NAAT with typing
Sample a lesion when present; detection depends on lesion stage and specimen quality, not an exposure countdown.
Seek sampling before a lesion heals; a negative result, particularly from an older lesion, does not exclude HSV.
Specimens: Swab from a fresh oral, genital or anal lesion
Sources 1
-
Type-specific HSV-1 IgG, only for an appropriate clinical question
No reliable universal clearance window for HSV-1 is established by this guidance; serology has sensitivity and localization limitations.
Do not label the HSV-2 12-week repeat recommendation as a guaranteed HSV-1 rule-out threshold.
Specimens: Blood
Sources 1
Early negatives, after treatment, and screening limits
An early negative result. A negative lesion swab or HSV-1 blood test does not automatically rule out infection. Assessment depends on symptoms, lesion timing and the assay.
After treatment. Antibodies can persist; herpes blood tests are not tests of cure. Repeated blind swabs without lesions do not establish absence of shedding.
Screening limits. Routine asymptomatic herpes serologic screening is not generally recommended. HSV IgM testing is not recommended.
Kissing and body sites. After kissing, a new oral lesion is the useful diagnostic target. A positive HSV-1 blood test cannot identify the recent kiss or distinguish oral from genital infection.
Sources for testing guidance (1)
- CDC STI Treatment Guidelines. Genital Herpes: virologic and type-specific serologic testing. 2021. cdc.gov
HSV-2: when to test after a possible exposure
Swab new lesions promptly. If type-specific HSV-2 blood testing is indicated after suspected recent acquisition, CDC recommends repeating at 12 weeks.
When to be seen sooner. New lesions warrant prompt assessment and swabbing, not waiting until the 12-week blood-test point.
-
HSV PCR / NAAT with typing
Sample when a lesion is present rather than waiting for an antibody window.
Early fresh-lesion sampling is more informative than a late healed-lesion sample.
Specimens: Fresh genital, anal or other suspicious lesion
Sources 1
-
Type-specific HSV-2 IgG with appropriate confirmation
Repeat at 12 weeks after suspected acquisition when initial testing was negative and serology is clinically indicated.
This is a repeat-testing recommendation, not perfect sensitivity at exactly 12 weeks. Low-positive results may need an independent confirmatory method.
Specimens: Blood
Sources 1
Early negatives, after treatment, and screening limits
An early negative result. Repeat an early negative when clinically indicated. Confirm low-positive results where appropriate; a positive screen alone can be misleading.
After treatment. IgG is not a test of cure and cannot reliably date acquisition.
Screening limits. Routine serologic screening of asymptomatic people is not generally recommended; HSV IgM is not recommended.
Kissing and body sites. Blood serology does not prove oral shedding or transmission from a kiss; a lesion needs site-specific evaluation.
Sources for testing guidance (1)
- CDC STI Treatment Guidelines. Genital Herpes: virologic and type-specific serologic testing. 2021. cdc.gov
Treatment
Acyclovir, valacyclovir or famciclovir can treat episodes or suppress recurrences. Suppression can reduce HSV-2 transmission in studied discordant couples, but it does not eradicate latent virus. There is no licensed preventive HSV vaccine. Severe illness, eye involvement or possible neonatal exposure needs specialist care. [34]
Actions
1. Swab a fresh sore. PCR/NAAT with HSV typing works best while a new sore is present; a swab late in healing can miss it. A throat swab is not a general screen for genital herpes. [34]
2. Use blood tests selectively. Routine population serology is not recommended. Low-positive HSV-2 antibody results may need confirmation; HSV-1 antibodies do not reveal whether infection is oral or genital. [34]
3. Plan ahead together. Tell current and new partners before sex, talk about suppressive medicine and barriers, and avoid contact with the area during sores or early tingling. No fixed lookback can date a new diagnosis. In pregnancy, let the obstetric team know about genital symptoms or exposure. [34]
SCIENCE & CONTEXT
Herpes / the evidence
History
Descriptions of blistering disease long predate the ability to identify viral causes. Modern virology distinguished HSV types and latency. Randomized oral acyclovir studies in the early 1980s established effective symptom treatment; a 2004 trial demonstrated reduced partner transmission with daily valacyclovir. Treatment has improved substantially, but a routine eradication cure remains unavailable. [34][35][37]
Impact
After initial infection, HSV remains latent in nerve cells and can reactivate. Genital HSV-2 generally recurs and sheds more often than genital HSV-1. First episodes can be painful or systemic; many later episodes are mild or unnoticed. Serious complications are uncommon in healthy adults but matter in newborns, some immunocompromised people and eye disease. [34]
A positive antibody result is evidence of infection, not a measurement of infectiousness today. US 2015-2016 seroprevalence was 47.8% for HSV-1 and 11.9% for HSV-2 among ages 14-49. These are historical national values, not prevalence estimates for every age, location or sexual network. [36]
Probability at a glance
Chance that at least one recent partner has herpes antibodies, by number of partners in six months, using historical US figures. Antibodies show past infection, not that anyone is shedding virus now.
| Partners | HSV-1: 47.8% | HSV-2: 11.9% |
|---|---|---|
1-2 | 47.8–72.8 | 11.9–22.4 |
3-5 | 85.8–96.1 | 31.6–46.9 |
6-10 | 98.0–99.8 | 53.2–71.8 |
11-20 | >99.9 | 75.2–92.1 |
Calculated probability of at least one antibody-positive partner using those historical US estimates. This is neither a genital-site estimate for HSV-1 nor the probability of encountering shedding or acquiring infection. [36]
In short: herpes is very common. Reduce risk where you can, and do not read a positive result as a judgement about anyone's behavior, faithfulness or when it was acquired.