Herpes simplex virus (HSV) is a common, lifelong infection carried by billions of people worldwide. It comes in two types: HSV-1, which primarily causes oral cold sores, and HSV-2, which primarily causes genital herpes. More than 1 in 5 adults between ages 15 and 49 are living with a genital herpes infection globally, and oral HSV-1 is even more widespread than that.
HSV-1 vs. HSV-2
Both types belong to the same virus family and behave similarly at the cellular level, but they differ in where they typically show up and how often they return.
HSV-1 spreads mainly through oral contact: kissing, sharing utensils, or touching saliva or skin around the mouth. It causes the familiar cold sores on or around the lips. However, HSV-1 can also be transmitted to the genitals through oral sex, making it an increasingly common cause of genital herpes as well.
HSV-2 spreads through sexual contact with genital or anal skin, sores, or fluids. It almost exclusively causes genital infections. Importantly, genital HSV-2 is much more likely to cause recurring outbreaks than genital HSV-1. Someone with genital HSV-1 may have one or two episodes and rarely experience another, while genital HSV-2 can reactivate multiple times per year, especially in the first year or two after infection.
You can carry both types simultaneously. WHO estimates from 2020 put the number of people aged 15 to 49 with genital HSV-2 at 520 million, with an additional 376 million living with genital HSV-1.
How the Virus Enters Your Body
HSV is an enveloped virus, meaning it’s wrapped in a fatty outer layer studded with surface proteins. When the virus reaches skin or mucous membranes, those surface proteins latch onto receptors on your cells and trigger the virus’s outer layer to merge with the cell membrane. This creates a tiny pore that lets the virus’s inner machinery slip inside.
Once inside the cell, the virus’s genetic material travels to the cell’s nucleus, where it hijacks the cell’s own machinery to make copies of itself. In skin and mucous membrane cells, this replication happens rapidly and eventually destroys the host cell, releasing new virus particles that infect neighboring cells. That wave of cell destruction is what produces visible sores.
Why the Virus Never Leaves
After the initial infection at the skin surface, HSV travels along nerve fibers into clusters of nerve cells called ganglia. HSV-1 typically settles in the trigeminal ganglia near the base of the skull, which supply sensation to the face. HSV-2 typically takes up residence in the sacral ganglia at the base of the spine, which serve the genital area.
Inside these nerve cells, the virus goes quiet. It stops replicating and essentially hides its DNA in the neuron’s nucleus, invisible to the immune system. This dormant state, called latency, is what makes herpes a lifelong infection. No current treatment can reach the virus while it’s latent in nerve tissue.
Periodically, the virus reactivates. Stress proteins inside the neuron shift location in a way that flips the virus back into its active state. The virus then travels back down the nerve fiber to the skin surface. Sometimes this produces a full outbreak with visible sores. Other times, the immune system shuts it down quickly, often within two to six hours, with no symptoms at all. These brief, invisible bursts of activity are called asymptomatic shedding, and they’re one reason the virus spreads so easily: a person can transmit HSV without knowing they’re infectious.
What an Outbreak Feels Like
A herpes outbreak follows a predictable pattern. Up to 48 hours before blisters appear, you may notice tingling, itching, or burning at the site where the sores will form. This warning phase is called the prodrome. Some people also develop a low fever, headache, or swollen lymph nodes during this time, particularly during a first outbreak.
Small fluid-filled blisters then appear, typically in clusters. Over the next few days they break open, forming shallow, painful ulcers. The ulcers gradually crust over and heal. A first episode tends to be the most severe and can take 7 to 10 days or longer to resolve. Recurrent outbreaks are usually milder and shorter.
Many people with HSV never develop noticeable symptoms at all. They carry the virus, shed it intermittently, and may never realize they’re infected.
How It’s Diagnosed
When a visible sore is present, the most reliable test is a PCR swab taken directly from the lesion. This detects the virus’s DNA and can distinguish between HSV-1 and HSV-2.
When no sore is present, blood tests can look for antibodies your immune system has made against the virus. These tests are less straightforward than they sound. The standard HSV-1 blood test has a sensitivity of only about 70%, meaning it misses roughly 3 in 10 infections. The HSV-2 blood test catches more infections (about 92% sensitivity) but has a specificity of just 57% compared to the gold-standard Western blot, which means false positives are common, especially at lower antibody levels. Current guidelines recommend confirming any borderline-positive HSV-2 blood result with a more specific test like the Western blot, though access to that test is limited.
IgM antibody testing, which attempts to detect recent infection, is not recommended. IgM tests can’t distinguish between HSV-1 and HSV-2, and they can turn positive during recurrent episodes or asymptomatic shedding, making results unreliable.
Treatment and Outbreak Management
Antiviral medications can shorten outbreaks and reduce their frequency, but they don’t eliminate the virus from the body. For a first genital herpes episode, a course of oral antivirals typically runs 7 to 10 days, with the option to extend if sores haven’t fully healed. Recurrent episodes can be treated with a shorter course started at the first sign of symptoms.
People who experience frequent outbreaks (roughly six or more per year) often benefit from daily suppressive therapy, where they take a low dose of an antiviral every day. This reduces the number of outbreaks and also lowers the amount of asymptomatic shedding, which decreases the chance of transmitting the virus to a partner.
For oral herpes, mild cold sores often resolve on their own. Topical and oral antivirals can speed healing if started early during the prodrome phase.
Reducing Transmission Risk
HSV spreads through direct skin-to-skin or skin-to-mucous-membrane contact. Condoms reduce the risk but don’t eliminate it, because the virus can shed from skin not covered by a condom. Avoiding sexual contact during active outbreaks significantly lowers transmission risk, since viral load is highest when sores are present. Daily suppressive antiviral therapy, combined with condom use, offers the greatest reduction in transmission risk for couples where one partner has genital herpes and the other does not.
For oral herpes, avoiding kissing or sharing utensils during an active cold sore reduces spread. Parents and caregivers with active cold sores should be especially careful around newborns.
Serious Complications
For most people, herpes is a manageable nuisance rather than a dangerous illness. But in certain situations, HSV can cause severe harm.
Neonatal herpes occurs when a baby is exposed to the virus during delivery, most often when the mother has a new genital herpes infection near the time of birth. The newborn’s immature immune system can allow the virus to spread to the brain and organs, making this a medical emergency. A mother with a known herpes history is typically managed during pregnancy to minimize this risk.
Herpes encephalitis is a rare but life-threatening condition where the virus infects the brain, causing inflammation, confusion, seizures, and potentially permanent neurological damage. It requires immediate treatment.
HSV keratitis is an eye infection that can lead to corneal scarring and, if untreated, blindness. People who have had one episode of HSV keratitis are at risk for recurrences, and wearing contact lenses may further increase that risk.
People with weakened immune systems, such as those undergoing chemotherapy or living with advanced HIV, are more vulnerable to severe or prolonged HSV outbreaks and complications.