Herpes (HSV) 1 IgG Test

Most adults carry herpes simplex virus type 1 and have no idea. The virus typically enters the body during childhood through casual contact, sets up permanent residence in nerve cells, and stays for life. An HSV-1 IgG (herpes simplex virus type 1 immunoglobulin G) test tells you one thing clearly: whether your immune system has ever encountered this virus.

That answer matters more than you might expect. Roughly 58% of Americans aged 14 to 49 carry HSV-1 antibodies, and the number climbs above 80% in many parts of Europe and Asia by middle age. A positive result places you in the majority. A negative result, increasingly common in younger adults, means you remain susceptible to a first infection that could show up genitally rather than orally, a shift that infectious disease researchers have been tracking for two decades.

What This Test Actually Measures

HSV-1 IgG is an antibody, a Y-shaped protein made by specialized white blood cells called plasma cells. After your first HSV-1 infection, your immune system produces these antibodies and maintains them indefinitely. The test detects their presence in your blood using a technique called ELISA (enzyme-linked immunosorbent assay), which targets a specific viral surface protein called glycoprotein G. This protein is unique to HSV-1, which is how the test distinguishes it from HSV-2.

The result is essentially binary: positive or negative, with a narrow equivocal zone in between. A positive result means you have been infected. It does not tell you when you were infected, where the virus lives in your body (oral versus genital), how often it reactivates, or whether you are currently shedding virus. Research on 82 people with first-episode genital HSV-1 showed that viral shedding is frequent in the first year but declines rapidly, yet shedding patterns bear no relationship to antibody levels.

What a Positive Result Does Not Mean

Three common misreadings deserve correction. First, a positive HSV-1 IgG does not mean you have genital herpes. The blood test detects antibodies to the virus type, not the location of infection. Many people with positive HSV-1 IgG acquired the virus orally in childhood and have never had a genital outbreak. Second, the number on the report (the index value or titer) does not track disease activity. Studies of over 1,300 people with and without severe mental illness found higher HSV-1 IgG concentrations in patients with schizophrenia and bipolar disorder, but within any group, titer levels overlap enormously and do not predict who will have symptoms.

Third, this test is almost never included in a routine blood panel or standard STI screen. If you have not specifically ordered it, you do not know your status. The test must be requested by name.

Dementia and Cognitive Decline

The most studied long-term association with HSV-1 seropositivity is dementia risk. A prospective study of 1,002 Swedish adults aged 70 and older found that people carrying HSV antibodies had roughly twice the risk of developing dementia over the follow-up period compared to those who were seronegative. A separate study of 3,432 adults in the Betula aging cohort found that reactivated herpes simplex infection, indicated by the presence of IgM antibodies (a class of antibody that appears during active or recent infection) alongside IgG, nearly doubled Alzheimer's disease risk, while IgG positivity alone did not significantly predict Alzheimer's.

That distinction matters. It suggests the risk may come from the virus periodically waking up and triggering inflammation, not simply from carrying antibodies. Research on 147 early Alzheimer's patients found that a specialized measurement of HSV antibodies inside the spinal fluid (not the standard blood test) correlated with markers of tau protein damage in the brain. Tau is a structural protein in brain cells, and its breakdown is one of the hallmarks of Alzheimer's progression. But standard serum HSV-1 IgG levels showed no such association in a different cohort.

For you, the takeaway is measured: being HSV-1 positive is extremely common and most seropositive people never develop dementia. But if you are seropositive and have a family history of Alzheimer's, this is context worth discussing with a physician, particularly as clinical trials testing whether antiviral treatment (valacyclovir) can slow cognitive decline in seropositive Alzheimer's patients are underway.

Heart Disease

A 2025 systematic review and meta-analysis pooling 11 studies (three cohort, eight case-control) found that HSV-1 IgG seropositivity was associated with about a 56% higher risk of coronary heart disease compared to seronegativity (pooled relative risk 1.56), though the studies varied considerably in how they measured and adjusted for other risk factors. At least one well-designed cohort from the UK found no association with composite cardiovascular disease after full adjustment (hazard ratio 0.93). No consistent signal emerged for stroke.

A separate line of evidence looked at "pathogen burden," the total number of chronic infections a person carries (including HSV-1, HSV-2, cytomegalovirus, and hepatitis A). Risk of heart attack or death rose in a dose-response pattern with the number of positive infections, suggesting the cardiovascular signal may come from cumulative immune activation rather than HSV-1 specifically.

Other Associations

In a study of 67 patients with autoimmune encephalitis (a condition where the immune system attacks the brain), HSV-1 IgG positivity and antibody levels against a specific viral protein were elevated compared to controls, raising the possibility that HSV-1 infection triggers some cases of autoimmune brain inflammation. A Mendelian randomization study, which uses genetic variation to approximate a randomized experiment, found a small but statistically significant causal link between genetically predicted HSV-1 IgG positivity and sepsis risk (about 7% higher odds).

These are population-level statistical signals. They do not mean a positive HSV-1 IgG result predicts any of these conditions for you individually.

Interpreting Your Result

Because HSV-1 IgG is a binary marker, there are no "optimal" or "borderline" tiers the way there are for cholesterol or blood sugar. Manufacturers set their own cutoffs for positive, equivocal, and negative. A typical scheme looks like this:

These cutoffs are assay-specific and will differ between labs. The Focus HerpeSelect HSV-1 ELISA, one of the most widely used platforms, has about 99% sensitivity but only 77% specificity, meaning false positives can occur, especially at low positive index values. The BioPlex platform showed 94% sensitivity and 96% specificity in head-to-head testing. If your result is low-positive (index value just above the cutoff), confirmatory testing with a different method is worth considering.

When Results Can Be Misleading

The biggest source of error is timing. If you were recently exposed to HSV-1 for the first time, your body may not have produced detectable IgG yet. In studies of people with culture-confirmed first-episode genital HSV-1, most sera drawn within 30 days were still IgG-negative on two different commercial platforms. If you are testing because of a recent possible exposure or a new lesion, a negative result does not rule out infection. Retest at least 12 to 16 weeks after the suspected exposure.

Severe immune suppression from high-dose corticosteroids, chemotherapy, or advanced HIV can blunt antibody production and produce falsely low or negative results. Common medications like statins, metformin, thyroid drugs, and PPIs have no known effect on HSV-1 IgG levels. Day-to-day factors like meals, exercise, and sleep do not shift antibody levels in any meaningful way, since IgG concentrations change over weeks to months, not hours.

Why One Reading Is Usually Enough

Unlike most biomarkers covered on this site, HSV-1 IgG does not benefit from serial trending. Once you are positive, you stay positive for life. Once you are negative, you remain negative unless you acquire the infection. The test answers a permanent question, not a fluctuating one.

The exceptions are narrow. If your first test was equivocal or low-positive, a repeat test in 4 to 6 weeks clarifies whether you are truly seropositive or whether the initial result was a false positive. If you tested negative but had a known recent exposure, retesting at 12 to 16 weeks captures delayed antibody development. Beyond these scenarios, there is no reason to retest.

What to Do With Your Result

A negative result means you have not been infected. If you are sexually active, this means you are susceptible to genital HSV-1, which now accounts for a growing share of genital herpes cases, particularly first episodes. In Europe, as many as two-thirds of young adults now reach sexual debut without HSV-1 antibodies, making genital acquisition increasingly common.

A positive result confirms past infection. The virus remains dormant in your nerve cells indefinitely. For most healthy adults, no further workup or treatment is needed. If you are experiencing recurrent outbreaks (oral or genital), this result helps your physician classify the infection by type and discuss suppressive antiviral therapy. If you are pregnant or planning pregnancy and your partner's HSV status differs from yours, this information feeds into neonatal risk assessment.

If you are seropositive, concerned about cognitive decline, and have a family history of Alzheimer's disease, consider discussing the emerging HSV-dementia research with a neurologist. There are no guidelines yet recommending antiviral treatment for dementia prevention based on HSV antibody status alone, but clinical trials are actively investigating this question. For cardiovascular risk, HSV-1 IgG positivity adds minimal information beyond standard lipid and inflammatory markers and does not warrant additional cardiac workup on its own.