Herpes simplex virus (HSV) uses both lytic and latent cycles, switching between them depending on which type of cell it infects. During an active outbreak, the virus is in its lytic phase, replicating inside skin cells and destroying them. Between outbreaks, it enters a latent phase in nerve cells, where it goes silent and produces no new virus. This latent phase is functionally similar to what biology textbooks call the lysogenic cycle, though the term “lysogenic” technically applies to bacteria-infecting viruses. In virology, HSV’s dormant state is called latency rather than lysogeny, but the concept is the same: the viral DNA persists inside a host cell without killing it.
The Lytic Phase: Active Infection
When HSV first infects you, it targets epithelial cells in the skin or mucous membranes. The virus attaches to the cell surface, fuses with the membrane, and injects its DNA into the cell’s nucleus. From there, it hijacks the cell’s machinery to copy itself in an ordered sequence: first it makes proteins that take control of the cell, then proteins that replicate its DNA, and finally structural proteins that assemble into new virus particles.
Those newly assembled particles exit the cell by budging through its membrane, which destroys the cell in the process. This is what causes the blisters and sores associated with herpes outbreaks. Each destroyed cell releases a fresh batch of virus that infects neighboring cells, spreading the infection outward. During a primary infection, this lytic replication happens rapidly in epithelial tissue before the immune system can mount a full response.
The Latent Phase: Going Silent in Nerve Cells
While the virus is replicating in skin cells, some viral particles reach the endings of nearby sensory nerves. The virus then travels backward along the nerve fiber toward the nerve cell body, a process called retrograde transport. It rides along tiny tracks inside the nerve (microtubules), pulled by a molecular motor called dynein, until it reaches clusters of nerve cells known as sensory ganglia near the spine or base of the skull.
Once inside a neuron, the virus does something fundamentally different. Instead of replicating and destroying the cell, it goes quiet. The viral DNA forms a circular loop (called an episome) inside the neuron’s nucleus but does not integrate into the cell’s own DNA. Nearly all viral genes shut down. The virus produces no new particles, causes no cell damage, and is essentially invisible to the immune system. This is what makes herpes a lifelong infection: the latent virus sits safely inside nerve cells that the body cannot afford to destroy and rarely replaces.
Neurons are a uniquely hospitable environment for this strategy. Unlike most cells, neurons don’t divide, which means the viral DNA isn’t disrupted by cell division. The virus doesn’t need to manipulate the cell cycle the way it would in other cell types. It simply sits and waits.
How the Virus Stays Silent
During latency, only one viral gene product is actively made: the latency-associated transcript, or LAT. This is a non-protein-coding RNA, meaning it doesn’t build anything. Instead, it acts as a molecular silencer, repressing the rest of the viral genome to keep the virus from accidentally switching back on.
Research published in PLOS Pathogens showed that when LAT is absent, viral genes become active more frequently and the virus reactivates at higher rates. LAT appears to work by influencing how tightly the viral DNA is packaged around proteins called histones. Tighter packaging makes genes harder to read, keeping the virus locked in its dormant state. In essence, LAT is the virus’s own insurance policy against premature reactivation, ensuring it stays hidden until conditions favor a new round of replication.
What Triggers the Switch Back to Lytic
Periodically, something disrupts the balance that keeps the virus latent, and it reactivates. The viral DNA begins producing lytic-phase genes again, new virus particles travel back down the nerve fiber to the skin surface, and the lytic cycle restarts in epithelial cells. This can cause a visible outbreak or, more commonly, produce no symptoms at all.
Known reactivation triggers include:
- Physical stress: UV light exposure, tissue trauma, surgery, or illness
- Psychological stress: emotional stress activates the body’s stress-hormone system, releasing cortisol and epinephrine, which can both suppress immune surveillance and directly stimulate viral reactivation in neurons
- Hormonal shifts: high estrogen levels can directly promote reactivation by acting on neurons harboring latent virus, while progesterone can inhibit the immune cells that help keep the virus in check
- Immune suppression: anything that weakens immune function, from medications to other infections
- Nutritional deficiencies: low levels of vitamins B12, C, and D have been linked to impaired immune regulation and increased reactivation risk
Asymptomatic Shedding: Lytic Without Symptoms
One of the more surprising aspects of HSV’s lytic phase is that it often happens without any visible signs. This is called asymptomatic shedding: the virus is actively replicating and present on the skin surface, but there are no sores or discomfort. A University of Washington study tracking people with new genital HSV-1 infections found that participants shed virus on about 12% of days at two months after infection. By 11 months, that dropped to 7% of days, and in those who shed most frequently, the rate eventually fell to just 1.3% of days. In most instances, participants had no symptoms during shedding episodes. This means the virus can cycle back into lytic replication at a low level without you ever knowing it.
Why the Distinction Matters
The dual-cycle nature of herpes is the reason it cannot be cured with current medicine. Antiviral medications work by interfering with viral replication during the lytic phase. They can shorten outbreaks, reduce shedding, and lower transmission risk. But they have no effect on latent virus sitting silently in neurons, because there is nothing to target: the virus isn’t replicating or producing the proteins those drugs act on.
So when you see the question framed as “lytic or lysogenic,” the accurate answer is that herpes is both, at different times and in different cell types. It is lytic in skin and mucosal cells during active infection, and latent (the equivalent of lysogenic) in sensory neurons between outbreaks. The ability to toggle between these two states is what makes herpesviruses so successful and so persistent.