Herpes simplex is a common viral infection caused by two closely related viruses: HSV-1 and HSV-2. Together, they infect the majority of the world’s population. In 2020, an estimated 3.8 billion people under age 50 (64% of the global population) had HSV-1, while roughly 520 million people aged 15 to 49 (13%) had HSV-2. Most carriers never develop noticeable symptoms, which is a major reason the virus spreads so efficiently.
HSV-1 vs. HSV-2
Both types belong to the same viral family and share most of their genetic code, but they differ in where they typically show up and how they behave. HSV-1 is traditionally associated with oral infections (cold sores), while HSV-2 is the more common cause of genital herpes. That said, HSV-1 increasingly causes genital infections too, usually through oral-to-genital contact.
The two viruses are genetically distinct enough that blood tests can tell them apart. A surface protein called glycoprotein G differs significantly between the two types, and this difference is the basis for type-specific antibody testing. Beyond diagnostics, the viruses also differ in subtle biological ways. HSV-1 is better at blocking a form of programmed cell death triggered by certain stressors, while HSV-2 does not block this same pathway as effectively. These molecular differences help explain why the two types behave differently in the body, including how often they reactivate.
How the Virus Enters and Stays in Your Body
When you’re first exposed, herpes simplex infects skin or mucous membrane cells and replicates there. This initial, active phase is what can produce visible sores. But the virus doesn’t stop at the surface. It enters the free nerve endings embedded in the infected skin and travels along the nerve fiber, moving deeper into the body toward clusters of nerve cells called ganglia.
HSV-1 typically settles in the trigeminal ganglion near the base of the skull, which supplies sensation to the face and mouth. HSV-2 usually takes up residence in the sacral ganglia at the base of the spine, which serve the genital and lower body area. Once inside these nerve cells, the virus goes quiet. It stops replicating and instead produces a single molecule called the latency-associated transcript, which helps it remain hidden from the immune system indefinitely.
This latent phase is what makes herpes a lifelong infection. The virus isn’t actively doing anything harmful while dormant, but it can reactivate periodically, traveling back down the nerve to the skin surface where it either causes a visible outbreak or sheds invisibly.
Symptoms and Outbreak Timeline
Many people with herpes simplex never notice symptoms, or their symptoms are mild enough to be mistaken for something else. Only about 205 million of the estimated 520 million people with genital HSV-2 experienced even one symptomatic episode in 2020.
When symptoms do occur, an outbreak typically follows a predictable pattern. It begins with a prodromal phase lasting a few days, during which you might feel tingling, burning, or itching in the area where sores are about to appear. This is the virus reactivating and traveling back to the skin surface. Small fluid-filled blisters then emerge, which break open into shallow, painful ulcers. These ulcers gradually crust over and heal, usually within two to three weeks for a first outbreak and faster for recurrences.
First outbreaks tend to be the most severe. They can come with flu-like symptoms including fever, body aches, and swollen lymph nodes. Recurrent outbreaks are typically shorter, less painful, and less extensive. Over time, most people experience fewer and milder episodes as the immune system gets better at controlling the virus.
Transmission and Asymptomatic Shedding
Herpes spreads through direct skin-to-skin or mucous membrane contact. For oral herpes, this includes kissing or sharing items that touch the mouth during an active outbreak. For genital herpes, it spreads through vaginal, anal, or oral sex. The virus is most contagious when sores are present, but transmission without visible symptoms is common.
This is because of a phenomenon called asymptomatic shedding: the virus periodically reactivates and appears on the skin surface in small quantities without causing noticeable sores. Research tracking people with genital HSV-2 found that shedding without symptoms occurred on about 26% of days in the first year after the initial episode. That rate drops to around 13% between years one and nine, and to about 9% after ten years. This declining pattern mirrors the general trend of outbreaks becoming less frequent over time, but it means transmission is possible even years after infection with no visible signs.
How Herpes Is Diagnosed
Two main testing approaches exist, and the right one depends on whether you have active sores.
If you have a blister or open sore that hasn’t yet crusted over, a swab test is the most reliable option. A healthcare provider takes a sample directly from the lesion and tests it, usually with a PCR test that detects viral DNA. This method works best on fresh, unhealed sores. Once a sore starts crusting or healing, the chance of getting an accurate result drops.
If you don’t have active sores but want to know your status, a blood test can detect antibodies your immune system has produced against the virus. The limitation is timing: after exposure, it can take up to 16 weeks or longer for antibody levels to become detectable. A blood test taken too soon after exposure may come back negative even if you’re infected. Type-specific blood tests can distinguish between HSV-1 and HSV-2 antibodies, which matters for understanding your risk of transmitting the virus and what to expect going forward.
Treatment and Managing Outbreaks
There is no cure for herpes simplex, but antiviral medications significantly reduce the severity and frequency of outbreaks. Three oral antivirals are used: acyclovir, valacyclovir, and famciclovir. All three work by interfering with the virus’s ability to copy itself, which shortens outbreaks and reduces the amount of virus on the skin.
These medications can be taken in two ways. Episodic therapy means taking the antiviral at the first sign of an outbreak (ideally during the tingling prodromal phase) and continuing for 7 to 10 days for a first episode, or a shorter course for recurrences. Suppressive therapy means taking a lower dose every day on an ongoing basis. Daily suppressive therapy is particularly useful for people who have frequent outbreaks or who want to reduce the risk of transmitting the virus to a partner. Daily valacyclovir has been shown to significantly decrease the rate of HSV-2 transmission in couples where one partner is infected and the other is not.
Reducing Transmission Risk
Condoms provide partial but meaningful protection. A pooled analysis of clinical data found that consistent condom use reduced the risk of acquiring HSV-2 by about 30% compared to never using condoms. Each additional increase in condom use further lowered the risk: for every 25% increase in the proportion of sexual encounters where condoms were used, acquisition risk dropped by about 7%. Conversely, each unprotected sexual encounter increased the risk by about 16%.
Condoms don’t fully eliminate risk because herpes can affect skin areas that a condom doesn’t cover. Combining condom use with daily suppressive antiviral therapy offers stronger protection than either strategy alone. Avoiding sexual contact during active outbreaks, when the virus is most concentrated on the skin, further reduces transmission.
Pregnancy and Newborn Risk
Herpes simplex during pregnancy raises specific concerns because the virus can be transmitted to the baby during delivery. The level of risk depends heavily on when the mother acquired the infection. A woman experiencing her first outbreak near the time of delivery carries a transmission risk of around 57%, because her body hasn’t yet built up antibodies that would partially protect the newborn. For women with a recurrent infection (meaning they were infected well before pregnancy), the risk drops to about 2%, because existing maternal antibodies cross the placenta and offer the baby some protection.
Neonatal herpes, though rare, can be serious, potentially affecting the baby’s skin, eyes, central nervous system, or internal organs. For this reason, women with active genital lesions at the time of labor are typically offered a cesarean delivery to avoid exposing the baby to the virus in the birth canal. Suppressive antiviral therapy in the final weeks of pregnancy is a common strategy to reduce the chance of an active outbreak at delivery.