HSV-1 vs. HSV-2: What's the Difference? (2024)

Herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) are two highly contagious viruses that can cause outbreaks of watery blisters on the skin and mucous membranes of the mouth, lips, nose, genitals, rectum, and eyes.

Although HSV-1 is more commonly associated with oral herpes (cold sores) and HSV-2 is more commonly linked to genital herpes, they can be passed to other parts of the body through oral sex. Because of this, it is possible for a cold sore to be caused by HSV-2 and a genital herpes outbreak to be caused by HSV-1.

Today, there is an increasing crossover between the two herpes types, and only diagnostic testing can reveal which virus is causing which type of infection. Differentiating the two can be important as the treatment approach for each can differ significantly.

This article looks at the differences and similarities between HSV-1 and HSV-2, including their symptoms and causes and how each is diagnosed and treated.

Symptoms

The majority of HSV infections are asymptomatic (meaning with little or no symptoms) and may never cause symptoms. In people who are symptomatic (with symptoms), HSV-1 and HSV-2 mainly differ by where the episode, called outbreaks, occurs.

In most cases, HSV-1 is passed through mouth-to-mouth contact, causing oral herpes (also known as herpes labialis), while HSV-2 is almost exclusively passed through sexual contact, causing genital herpes (or herpes genitalis).

Beyond the location of the outbreak, the symptoms of HSV-1 and HSV-2 are largely indistinguishable.

In symptomatic people, HSV-1 and HSV-2 both develop in characteristic stages:

1. Prodromal stage: This is the early stage of infection. There may be redness, swelling, and a burning or tingling sensation at the site of the impending outbreak. Headache, fatigue, weakness, swollen lymph nodes, and fever may accompany the infection.
2. Blister stage: The prodromal symptoms are quickly followed by the outbreak of tiny blisters filled with clear to whitish-yellow fluid. The blisters tend to develop in clusters and can be very tender.
3. Eruptive stage: This is the stage when the blisters break open and leak fluids, leaving painful open sores (ulcers) that quickly crust over.
4. Healing stage: After about four toseven days, the crusted sores will start to scab and heal. The healing process can take anywhere from one to three weeks. First outbreaks tend to take longer and be more severe than subsequent outbreaks.

Is It HSV-1 or HSV-2?

While it may seem reasonable to assume that a cold sore is caused by HSV-1 and genital herpes is caused by HSV-2, a 2015 study in PLoS One suggested that more than half of all new genital herpes cases in people 14 to 49 are caused by HSV-1.

In the end, you cannot differentiate HSV-1 from HSV-2 by either the appearance or location of the outbreak. This can only be done with diagnostic testing.

One key difference between HSV-1 and HSV-2 is the risk of recurrence. All herpes viruses tend to recur (repeat) after the initial outbreak, often within the first year. But, with a genital herpes outbreak, HSV-1 is 80% less likely to recur within a year. In some cases, you would only have one outbreak with no recurrence.

In contrast, recurrence is common withHSV-2. If left untreated, some people may experience recurrent outbreaks anywhere from one to 12 times per year. Moreover, the recurrent episodes tend to be far more severe than with HSV-1 and can persist for many years.

Causes

HSV-1 and HSV-2 belong to a family of viruses called Herpesviridae, which also includes the varicella-zoster virus (VZV) cauaing chicken pox and shingles.

As with VZV, HSV-1 and HSV-2 are never cleared from the body after the infection. Instead, the viruses embed themselves in nerve cells, where the viruses remain in a latent (dormant) state. In some people, HSV-1 and HSV-2 can spontaneously reactivate and cause a new outbreak of oral or genital herpes.

During reactivation, a process known as viral shedding occurs in which the herpes virus starts to multiply and migrate to the skin at the site of the initial infection. It is then that the virus can be transmitted (passed) to others through close physical contact.

The transmission can occur both when there are visible sores and also when a person with HSV-1 or HSV-2 is asymptomatic. This is known as asymptomatic shedding.

In fact, according to the Centers for Disease Control and Prevention (CDC), the transmission of HSV-2 most often occurs when a person is asymptomatic and may not even realize they have the virus.

While the same can occur with HSV-1, a genital HSV-2 infection is substantially more severe in terms of recurrences and viral shedding. With HSV-2, high rates of shedding can occur years after the first outbreak. Shedding with HSV-1 tends to wane quickly, and it becomes less transmissible.

Differences Between HSV-1 and HSV-2

While the mechanisms of transmission are similar, HSV-1 and HSV-2 vary in several key ways, including:

• Latent infection: During latency, HSV-1 tends to embed itself in a cluster of nerve cells called the trigeminal ganglia situated around the head and face. HSV-2, on the other hand, tends to embed itself in the sacral ganglia of the lower trunk and limbs. This explains why HSV-1 is more likely to affect the upper body, while HSV-2 is more likely to affect the lower body.
• Route of transmission: HSV-2 is nearly twice as common in females as in males. This is likely because genital infections are more easily passed from males to females during vagin*l sex. HSV-1 is only slightly more common in females than in males (50.4% vs. 45.8%), likely because the route of transmission (mouth-to-mouth) involves the same anatomy in people of all sexes.
• Declining infection rates: While rates of HSV-1 have decreased by more than 10% since the 1970s, the rate of genital HSV-1 has increased by more than 60%. Because fewer people are being exposed to HSV-1 during childhood (and therefore have no antibodies to the virus), they are more likely to experience a genital outbreak if exposed to the virus for the first time through oral sex.

Diagnosis of HSV-1 and HSV-2

HSV-1 and HSV-2 are both diagnosed in the same way and with the same tools. The tests are commonly used to:

• Determine whether sores on your mouth or genitals are caused by HSV.
• Diagnose herpes during pregnancy (to prevent transmission of the virus to the fetus).
• Find out if a newborn has herpes.

Newer herpes tests can detect herpes and differentiate between HSV-1 and HSV-2, the differentiation of which may influence the treatment plan.

Types of Tests

Herpes testing is usually done as a swab test, a blood test, or a lumbar puncture (spinal tap). The test you get will depend on the type of symptoms you have:

• Swab tests are used in symptomatic people to collect fluids and cells from a herpes sore. They can differentiate HSV-1 from HSV-2 based on their genetic material using a technology called polymerase chain reaction (PCR). This is the gold standard for herpes testing.
• Blood tests can be used in symptomatic or asymptomatic people. These include PCR tests and antibody-based tests (which detect immune proteins produced in response to the virus rather than the virus itself). Some antibody tests can differentiate HSV-1 and HSV-2, while others cannot. Testing too early in asymptomatic people can lead to a false-negative result, which claims a person does not have the infection when they actually do.
• Lumbar puncture is used when herpes is suspected to have spread to the brain and spinal cord, causing encephalitis. This is a rare complication mostly seen in immunocompromised people, such as those with advanced HIV (human immunodeficiency virus). The PCR test screens cerebrospinal fluid.

HSV blood testingmaybe useful if:

• Your sex partner has genital herpes, and you want to know if you acquired it.
• You are pregnant, and you and your partner have had genital herpes in the past or currently have genital herpes symptoms.

Treatment

HSV-1 and HSV-2 are both treated with antiviral drugs. The drugs don't "cure" herpes but rather prevent the virus from binding to and infecting healthy cells.

There are three oral antivirals approved for the treatment of HSV-1 and HSV-2:

• Zovirax (acyclovir)
• Valtrex (valacyclovir)
• Famvir (famciclovir)

While these drugs can treat both HSV-1 and HSV-2, how they are used can vary significantly based on which virus is involved and whether it is a first or subsequent outbreak.

For instance, if you have a cold sore, your healthcare provider will likely forego testing and prescribe a course of antivirals to shorten the duration and severity of the infection.

The same may not be true if you have genital herpes. While the differentiation of HSV-1 and HSV-2 won't necessarily alter the course of treatment, particularly during a first outbreak, it can when there is a recurrence.

According to the CDC, genital HSV-1 and HSV-2 should be treated in the following manner for first and recurrent episodes:

• First outbreak: Anyone with afirst episode of genital herpes should receive oral antiviral therapy, irrespective of whether they have HSV-1 or HSV-2. Treatment is prescribed for seven to 10 days.
• Recurrent HSV-2: Almost everyone with genital HSV-2 will experience recurrent outbreaks. In such cases, suppressive therapy (in the form of a daily antiviral drug) may be prescribed to lower the risk of recurrence and the odds of transmitting the virus to others. If there is an outbreak, episodic therapy can be prescribed for anywhere from one to five days to resolve the acute infection.
• Recurrent HSV-1: Recurrences are less common after a first outbreak of genital HSV-1. Because of this, episodic therapy is more commonly prescribed during incidental outbreaks. Suppressive therapy is reserved for uncommon cases in which outbreaks are more frequent and severe.

Prevention

The prevention strategies for HSV-1 and HSV-2 are largely the same but vary by the source of the transmission. As herpes is spread through direct, physical contact, the best method of prevention is toavoid physical contact with a person's herpes sores while they are having an outbreak.

With HSV-1, which is mainly spread through oral contact, this means avoiding kissing and any other contact with a cold sore.

To prevent the spread of HSV-1 to the genitals or anus, abstain from sex while you or a sex partner have visible sores or prodromal symptoms. If you have sex, you can reduce the risk of transmission by using condoms for oral-penile sex and dental dams for oral-vagin*l or oral-anal sex.

As HSV-2 is almost exclusively passed through sex, the same rules regarding abstinence, condoms, and dental dams apply. If you have HSV-2 and are prone to frequent recurrence, speak with your healthcare provider about daily suppressive antiviral therapy to reduce the risk of transmission.

Condoms provide only partial protection as the virus may be shed through skin not covered by the condom.

Summary

Herpes simplex virus type 1 (HSV-1) is more commonly associated with oral herpes (cold sores), while herpes simplex virus type 2 (HSV-2) is more commonly associated with genital herpes. Even so, HSV-1 is increasingly linked to genital herpes due to oral sex.

While the symptoms of HSV-1 and HSV-2 are indistinguishable. HSV-2 is more likely to recur and cause high levels of viral shedding years after the initial infection. Moreover, with HSV-2 especially, viral shedding can occur with no symptoms, meaning that the virus can be passed without a person even realizing they have herpes.

This is why screening is recommended for all people with genital herpes symptoms. The differentiation of HSV-1 and HSV-2 can influence the treatment plan, especially when there are frequent recurrences.