Herpes simplex virus infects skin or mucosal cells, travels into your nervous system, and hides there for life. It’s one of the most common infections on earth: around 846 million people between 15 and 49 have genital herpes alone, according to WHO estimates from 2020. The virus comes in two types, HSV-1 and HSV-2, and both follow the same basic playbook of infection, dormancy, and reactivation.
How the Virus Gets Into Your Cells
Herpes needs direct contact with skin or mucous membranes to spread. The virus can’t survive long outside the body, so transmission happens through kissing, sexual contact, or skin-to-skin contact with an active or shedding infection site. Once the virus lands on a vulnerable surface, it uses proteins on its outer envelope to latch onto matching receptors on your cells. The initial grab is loose, like Velcro catching fabric, as viral surface proteins hook onto sugar molecules coating your cells.
The real entry depends on a tighter lock-and-key fit. A specific viral protein binds to one of several receptors on the cell surface, with the two most important being nectin-1 (found on nerve and skin cells) and HVEM (found on immune cells). HSV-1 and HSV-2 both use these receptors but have slightly different preferences, which partly explains why HSV-1 favors the oral area and HSV-2 favors the genital area. Once this binding happens, the virus fuses its outer membrane with the cell membrane and dumps its genetic material inside. Four viral proteins work together to make this fusion happen, and without any one of them, the virus can’t get in.
What Happens During the First Infection
Once inside epithelial cells at the infection site, the virus hijacks the cell’s machinery to make copies of itself. Each infected cell produces new viral particles that burst out and infect neighboring cells, creating a spreading zone of damage. This is what produces the characteristic blisters: clusters of damaged cells filled with fluid containing millions of viral copies.
A first outbreak is typically the worst. Your immune system has never encountered the virus before, so it takes time to mount a response. You may experience flu-like symptoms, swollen lymph nodes, and painful sores that can last two to three weeks. Some people, though, have a first infection so mild they never notice it. Whether or not you have visible symptoms, the virus is doing the same thing underneath: replicating in surface cells and, critically, finding its way into nearby nerve endings.
How the Virus Hides in Your Nerves
This is the step that makes herpes a lifelong infection. While replicating in skin cells, the virus also enters the tips of sensory nerve fibers that reach the skin’s surface. It then rides along the nerve cell’s internal transport system, traveling backward (toward the spine or skull) until it reaches the nerve cell body in a structure called a ganglion. For oral herpes, that’s the trigeminal ganglion near the base of the skull. For genital herpes, it’s the sacral ganglia near the base of the spine.
Once inside the nerve cell body, the virus faces a fork in the road: keep replicating or go quiet. In neurons, the virus almost always chooses dormancy. It shuts down all of its active genes and coils its DNA into a compact, silent loop inside the nerve cell’s nucleus. At this point, the virus is producing almost no viral proteins, making it essentially invisible to your immune system. The infected neuron stays alive and functions normally. This dormant state is called latency, and it can last for the rest of your life.
What Keeps the Virus in Check
Your immune system doesn’t ignore latently infected neurons entirely. Specialized immune cells called CD8+ T cells take up permanent residence in the ganglia where the virus hides. These T cells appear to detect very low levels of viral protein that occasionally leak out during latency, and they respond by releasing a signaling molecule called interferon-gamma directly at the neuron. This chemical signal shuts down viral gene activity before the virus can assemble new copies of itself, all without killing the neuron.
Research on these immune cells shows they physically orient themselves toward the surface of infected neurons, with their receptor machinery pointed at the contact zone, like a guard pressing an ear to a door. This surveillance is continuous and remarkably effective. Most of the time, it prevents any viral particles from being produced. But it’s not perfect, and when it fails, even briefly, you get reactivation.
Why Outbreaks Come Back
Reactivation happens when something disrupts the balance between the dormant virus and the immune system holding it in place. The triggers people commonly report, including illness, stress, fatigue, sun exposure, menstruation, and physical trauma to the area, all have plausible biological mechanisms.
Psychological stress, for example, activates your body’s fight-or-flight system, flooding the nervous system with stress hormones like adrenaline and cortisol. Adrenaline binds to receptors on sensory neurons and triggers a chain of internal signals that can nudge the virus’s dormant genes back into action. Physical nerve damage works through a different route: calcium floods into the injured nerve cell and activates stress-response pathways that overlap with the signals needed to wake the virus. Both pathways converge on the same result: reactivation of viral gene expression in the neuron.
When the virus reactivates, it begins producing new copies of itself inside the nerve cell body, then ships those copies back down the nerve fiber to the skin’s surface. If enough virus reaches the skin and the immune response is slow, you get a visible outbreak. If the immune system catches it quickly, you may shed virus from the skin with no symptoms at all.
Viral Shedding Without Symptoms
This is one of the most important things to understand about herpes: the virus can be present on your skin and transmissible even when you feel completely fine. Studies using daily swabs from people with HSV-2 found that virus was detectable on roughly 12% of days overall, even when no sores were present. People who had never experienced a recognized outbreak still shed virus on about 9% of days tested. Those with a history of symptomatic outbreaks shed on about 13% of days between outbreaks.
This subclinical shedding is the primary way herpes spreads. Most new infections are transmitted by someone who doesn’t know they’re shedding virus at that moment. Shedding episodes are typically brief, often lasting less than a day, but they happen frequently enough to make transmission a real possibility over time.
What an Outbreak Looks and Feels Like
Many people feel a reactivation coming before they see anything. This warning phase, called the prodrome, can include tingling, itching, burning, or a shooting pain in the area where sores will appear. It typically begins a few hours to a couple of days before visible symptoms.
The outbreak itself progresses through distinct stages. Small, fluid-filled blisters appear first, usually in a cluster. These blisters rupture within a day or two, leaving shallow, painful ulcers that may ooze or bleed. Over the next several days, the ulcers dry out and form scabs. The entire cycle from first tingle to healed skin generally takes 7 to 10 days for recurrent episodes, shorter than a first outbreak. Recurrences tend to become less frequent and less severe over the years as the immune system builds a stronger response to the virus.
How Antiviral Medications Work
The most commonly used herpes treatments belong to a class of drugs that exploit a key difference between infected and uninfected cells. The active drug is essentially inert until it enters a cell that’s actively producing herpes virus. Inside that cell, a viral enzyme (not found in healthy cells) activates the drug by adding a chemical tag to it. Normal cells lack this enzyme and leave the drug untouched, which is why these medications cause very few side effects.
Once activated inside an infected cell, the drug mimics one of the building blocks of DNA. The viral copying machinery incorporates it into the growing DNA chain, but the drug molecule is missing a critical chemical hook needed to attach the next building block. The chain stops dead. Even better, the stalled complex permanently disables the viral copying enzyme itself. The result is a highly targeted attack: viral replication grinds to a halt in infected cells while healthy cells are barely affected.
These medications don’t clear the virus from your ganglia or cure the infection. What they do is shorten outbreaks, reduce their severity, and, when taken daily as suppressive therapy, decrease the frequency of outbreaks and lower the risk of transmitting the virus to a partner. Daily suppressive therapy has been shown to reduce HSV-2 transmission in couples where one partner is infected and the other is not.
Testing and Its Limitations
If you have active sores, the most reliable test is a swab of the sore itself, which can be tested for viral DNA. This directly confirms whether herpes virus is present and can distinguish between HSV-1 and HSV-2.
Blood tests work differently. They detect antibodies your immune system has made against the virus, not the virus itself. For HSV-2, the major commercial blood tests perform well, with sensitivity above 97% and specificity above 98%. For HSV-1, accuracy is more uneven: sensitivity drops below 85% on some platforms, meaning the test misses a meaningful number of infections. Blood tests also require time after infection for antibodies to develop, so testing too early after exposure can produce a false negative. The typical window is several weeks to a few months before antibodies reach detectable levels.