HSV (herpes simplex virus) is a common viral infection that causes painful blisters or sores, most often on the mouth or genitals. It comes in two types, affects over a billion people worldwide, and stays in the body for life. Most people with HSV don’t know they have it because symptoms can be mild or absent entirely.
Two Types of HSV
HSV-1 spreads mainly through oral contact, such as kissing or sharing utensils, and typically causes cold sores in or around the mouth. It can also cause genital herpes, usually through oral sex. HSV-2 spreads through sexual contact and almost exclusively causes genital herpes, producing sores around the genitals or anus.
The practical difference between the two goes beyond location. HSV-2 causes recurrent outbreaks far more often than genital HSV-1. HSV-2 also infects women nearly twice as often as men because sexual transmission is more efficient from male to female partners.
How Common Is HSV?
According to WHO estimates from 2024, around 846 million people between the ages of 15 and 49 are living with genital herpes infections globally. That’s more than 1 in 5 adults. Of those, roughly 520 million have genital HSV-2 and about 376 million have genital HSV-1. Oral HSV-1 is even more widespread, with the majority of the global population carrying it, often acquired in childhood.
How HSV Spreads
HSV-1 passes through contact with sores, saliva, or skin around the mouth. HSV-2 spreads through contact with genital or anal skin, sores, or fluids during sex. Crucially, HSV-2 can be transmitted even when the skin looks completely normal and the person has no symptoms at all.
This is possible because of something called asymptomatic shedding: the virus periodically becomes active on the skin’s surface without producing visible sores. Research tracking daily swabs in people with HSV-2 found that those who had never noticed symptoms still shed the virus on about 10% of days. People with recognized symptoms shed on about 20% of days. Even on days without any sores or tingling, the virus can be present and contagious.
What a First Outbreak Feels Like
When someone is first infected, symptoms typically appear 2 to 10 days after exposure. The first outbreak tends to be the worst. It often begins with flu-like symptoms: fever, chills, muscle aches, fatigue, and nausea. Then small blisters or bumps appear at the site of infection, either around the mouth (for oral herpes) or around the genitals and anus (for genital herpes).
Over several days, those blisters break open and release fluid, forming shallow, painful ulcers. The sores then crust over and heal without leaving scars. A first genital herpes outbreak typically lasts 2 to 4 weeks from start to finish. Subsequent outbreaks are usually shorter, less painful, and less frequent over time.
Many people never experience a noticeable first outbreak at all. They carry the virus without knowing it, which is one reason HSV spreads so easily.
Why HSV Never Leaves the Body
After the initial infection clears from the skin, HSV doesn’t disappear. The virus travels along nerve fibers and settles into clusters of nerve cells near the spine, where it enters a dormant state called latency. HSV-1 typically takes up residence in nerve clusters near the base of the skull (serving the face and mouth), while HSV-2 favors nerve clusters in the lower spine (serving the genital area). This is why each type tends to reactivate in its preferred location.
During latency, the virus is essentially invisible to the immune system. Periodically, it reactivates, traveling back along the nerves to the skin’s surface. Sometimes this causes a visible outbreak. Other times, the virus reaches the skin without producing symptoms, resulting in the silent shedding described above. Triggers for reactivation vary from person to person but commonly include stress, illness, fatigue, sun exposure, and hormonal changes.
How HSV Is Diagnosed
The most reliable way to diagnose HSV is through a swab taken directly from an active blister or sore that hasn’t yet crusted over. This test, which detects the virus’s genetic material, works best during an active outbreak when the virus is most concentrated.
If no sores are present, a blood test can check for antibodies the immune system produces in response to HSV. These tests have important limitations, though. It can take up to 16 weeks after exposure for antibodies to reach detectable levels, so testing too soon can produce a false negative. Blood tests for herpes also have a higher false positive rate than tests for infections like chlamydia or gonorrhea, which means a positive result sometimes needs to be confirmed with additional testing.
Treatment and Daily Management
There is no cure for HSV, but antiviral medications effectively shorten outbreaks, reduce their severity, and lower the risk of passing the virus to a partner. Three antiviral drugs are used: acyclovir, valacyclovir, and famciclovir. All work by blocking the virus’s ability to replicate.
Treatment falls into two main approaches. Episodic therapy means taking antivirals only when an outbreak occurs, ideally within the first day of symptoms. For a first episode of genital herpes, treatment typically lasts 7 to 10 days. For recurrent outbreaks, courses are shorter, ranging from 1 to 5 days depending on the specific medication and dosing schedule.
Suppressive therapy means taking a low dose of an antiviral every day, whether or not symptoms are present. This approach is often chosen by people who experience frequent recurrences (generally six or more outbreaks per year) or who want to reduce the risk of transmitting HSV to a sexual partner. Daily suppressive therapy significantly reduces both the frequency of outbreaks and the amount of asymptomatic viral shedding.
Risks During Pregnancy
The most serious complication of HSV is neonatal herpes, which occurs when a newborn is exposed to the virus during delivery. The risk depends heavily on timing. A mother who acquires a brand-new genital herpes infection near the time of delivery has a transmission risk as high as 57%, because her body hasn’t yet built up antibodies that help protect the baby. For mothers with a recurrent infection, meaning they were infected before pregnancy, the risk drops to about 2%.
This is why providers pay close attention to herpes status during pregnancy. Women with a history of genital herpes are often placed on daily antiviral therapy in the final weeks of pregnancy to suppress outbreaks. If active sores are present at the time of labor, a cesarean delivery is typically recommended to avoid exposing the baby to the virus during passage through the birth canal.
Reducing Transmission Risk
Condoms reduce the risk of HSV transmission but don’t eliminate it, because the virus can be present on skin not covered by a condom. Avoiding sexual contact during active outbreaks lowers risk further, since viral shedding is highest when sores are present. Combining condom use with daily suppressive antiviral therapy offers the greatest reduction in transmission risk for couples where one partner has HSV and the other does not.
For oral herpes, avoiding kissing or sharing cups and utensils during an active cold sore is the most practical precaution. Since HSV-1 can spread to the genitals through oral sex, avoiding oral-genital contact during an oral outbreak also matters.