How Herpes Is Diagnosed

Herpes simplex virus (HSV) types 1 and 2 can be diagnosed based on the appearance of lesions (if present), as well as with laboratory tests.

In general, if you do not have symptoms, there is no need for you to have any diagnostic testing for HSV type 1—the type that causes cold sores. However, if you may have been exposed to HSV type 2—a sexually transmitted disease (STD) that causes genital sores—you may need to be tested even if you do not have lesions.

herpes diagnosis
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Both HSV-1 and HSV-2 can cause visible skin lesions. It is important that you see a healthcare provider, especially if you've never had an outbreak before.

Once you've had herpes, you can learn to recognize recurrences of the lesions. But if your recurrences are more severe or if the lesions look different than usual, then you should seek an evaluation.

Herpes outbreaks usually appear as one or more blisters in clusters. The blisters may break open to become sores.

Cold sores in the mouth are usually caused by HSV 1, and genital herpes infections are usually caused by HSV 2. However, either virus can infect either location.

If you or your child experience pain or tingling around or inside the mouth or on the tongue, you can feel and look for bumps and blisters around the painful area, which may indicate HSV-1.

If you have pain in or around the genital area, or if you have pain with urination or sexual activity, look for redness, swelling, sores, or blisters in or around the affected area, which may indicate HSV-2.

Regardless, you should check for lesions if you think you could have been exposed to the infection. Know, though, that genital herpes infections are often asymptomatic.

Labs and Tests 

If you have symptoms of HSV type 1 or 2, your healthcare provider can diagnose a herpes infection by looking at your skin and/or by swabbing the sores to test for the herpes virus.

If you do not have obvious symptoms, a blood test can help determine whether you have an infection. 

Swab Testing

The gold standard for herpes diagnosis is a viral culture test or nucleic acid amplification test (NAT) of a sample of skin, crust, or fluid from a lesion. This is usually obtained with a gentle swab of the area.

A viral culture is a test that allows the virus to grow in a laboratory setting. The NAT tests for the genetic material of the virus in the sample.

These tests should only come back positive if you have the virus present in the lesion. In general, the results of the test are reliable if you have active lesions.  

Herpes Blood Tests

It is possible to screen for asymptomatic herpes infections using a blood test. Herpes blood tests can detect antibodies to the herpes virus.

You form these proteins when you need to fight an infection. Generally, it takes about two weeks for your body to produce enough antibodies against herpes to be detectable.

The presence of antibodies is evidence that your body has confronted an infection, either recently or in the past. The antibodies can last for years or even a lifetime, which is why using this test to identify reinfection is not helpful. 

There are two kinds of blood tests for herpes:

  • IgM tests detect short-lasting antibodies that form to fight the virus shortly after an infection has occurred.
  • IgG tests detect long-lasting antibodies that your body makes to fight the virus.

There are several different brands of blood tests that are used to detect viral proteins, and there are pros and cons for each.

It is difficult to know how long it takes for blood tests to become positive after infection with HSV-1. The median time from the onset of symptoms to a positive HSV-2 blood test is as follows:

  • HerpeSelect ELISA: 3 weeks 
  • Western blot: 1 to 3 months 
  • Kalon ELISA: 120 days
  • Focus ELISA: 21 days 

In general, it usually takes around two weeks for symptoms to appear after you have been infected with HSV type 1 or 2. If you do not have lesions that can be swab tested, it is a good idea to wait at least a month or two after your exposure before getting an HSV-2 antibody test. This is because it takes time for your body to make antibodies that can be detected in the blood. Testing before these antibodies develop can lead to a false-negative result.

There is some possibility that herpes blood tests may detect antibodies to similar viruses. This result would lead to a false-positive result, suggesting you have the infection when you don't.

If you have a strong reason to believe that you have been infected, you might want to consider getting retested after six months because some of the tests take longer to yield a positive result.

In Newborns

The diagnosis of neonatal herpes—infection passed to a child during or after childbirth—is challenging.

Generally, babies are not screened for herpes infection. Symptoms such as lesions around the mouth or eye may alert caregivers that there is a problem. This should prompt diagnostic testing, which can be done using a swab sample.

However, more complicated neonatal herpes infections, such as encephalitis (infection of the brain), require specific tests such as a spinal tap.

Differential Diagnoses

There are a few other conditions that can be confused with cold sores or genital herpes. Some of these are quite serious, and it is not safe for you to self-diagnose.

Typically, these conditions can be distinguished from herpes with a medical examination or with laboratory tests.  

  • Canker sores: Canker sores are usually red, raised sores with a painful, raw, whitish pit in the center. They may be present in the mouth, and they tend to occur as a result of oral trauma. The initial painful sensation of canker sores and cold sores is similar, but the lesions look different. Canker sores do not test positive for herpes simplex virus. 
  • Syphilis: An STD that produces painless genital sores, syphilis can be confused with herpes. Your healthcare provider may be able to tell the difference by visually inspecting the lesions. If you have syphilis, your blood tests should be positive for Treponema pallidum, the bacteria that causes the infection.
  • Medication reaction: Medications can cause allergies and sensitivity reactions, which may manifest as a rash. This is not generally common in the genital area, but it can often occur around the lips and mouth. 
  • Cancer/pre-cancer: Lesions in and around the genital area can be signs of cancer. Cancerous or pre-cancerous lesions should not have blisters, which are a common characteristic of HSV-induced lesions. But if your healthcare provider needs to distinguish between cancer and herpes, a swab or a needle biopsy (sample of the lesion) can differentiate the two conditions.
  • Concurrent HSV-1 and HSV-2: If you have HSV-1 or HSV-2, you can also become infected with the other. These are different viruses and having one of them does not cause or prevent the other. It is important to keep that in mind and to see your healthcare provider if you develop sores in a new location. 

Frequently Asked Questions

  • Can a blood test detect herpes?

    Yes. There are two types of blood tests for herpes: The IgM test can detect antibodies that are formed in the early stages of the infection. The IgG test detects antibodies that can be present long after the initial infection.

  • Can a urine test detect herpes?

    No. Urine tests are not used to detect herpes. Urine STD screenings test for chlamydia and gonorrhea.

  • Do healthcare providers usually test for genital herpes?

    Most healthcare providers do not routinely test for herpes unless you specifically ask or have symptoms including genital pain, redness, swelling, sores, or blisters. If you have been exposed to genital herpes or would like to be tested, talk to your healthcare provider. 

12 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Elizabeth Boskey, PhD
Elizabeth Boskey, PhD, MPH, CHES, is a social worker, adjunct lecturer, and expert writer in the field of sexually transmitted diseases.