Causes and Risk Factors of Herpes

Table of Contents
View All
Table of Contents

Both oral herpes and genitals herpes are caused by types of the herpes simplex virus (HSV). The virus is passed when you come in contact with a herpes sore or its fluids. The virus can also be passed through skin-to-skin contact when the virus is active in someone without symptoms (referred to as asymptomatic shedding).

Herpes simplex virus type 1 (HSV-1) is the type commonly associated with oral herpes (cold sores). Herpes simplex virus type 2 (HSV-2) is the type commonly associated with genital herpes. Even so, HSV-1 can be passed to the genitals and HSV-2 can be passed to the mouth via oral sex.

This article describes the different causes and risk factors for HSV-1 and HSV-2. It also explains who is at high risk for herpes and how to protect yourself.

herpes causes and risk factors
Illustration by Verywell

What Causes Herpes?

HSV-1 and HSV-2 are similar but distinct viruses that can be passed from person to person through physical contact or contact with fluid from a sore.

Once you are infected, the virus remains in your body for life. It embeds itself in nerve cells where it mostly remains in a latent (dormant) state.

Occasionally, the virus can reactivate, causing oral herpes when it develops on the mouth and genital herpes when it develops on the genitals or anus.

Not everyone who has HSV-1 or HSV-2 experiences outbreaks. In fact, most people with herpes do not have symptoms but can still pass the virus whenever it reactivates. This is referred to as asymptomatic shedding.

As such, a person can pass the herpes virus on without even knowing they have it.


HSV-1 is the type most commonly associated with oral herpes, also known as a cold sore, fever blister, orolabial herpes, or herpes labialis. The infection is typically spread between people through non-sexual contact, such as kissing or touching.

However, it can also be spread to the genitals through oral sex, including oral-vaginal sex (cunnilingus), oral-penile sex ("blow jobs"), or oral-anal sex ("rimming").

In fact, according to a 2013 study published in Clinical Infectious Diseases, HSV-1 has become the most common cause of genital herpes in young women, accounting for roughly 60% of all cases.

While an outbreak of HSV-1 on the genitals is indistinguishable from HSV-2—and can only be differentiated by a test known as a PCR—it is far less likely to recur. In some cases, an HSV-1 infection of the genitals is a one-time event.

The same is not necessarily true for an HSV-1 infection on the mouth or lip. In some people, symptoms can recur over many years.


HSV-2 is the type commonly associated with genital herpes, also known as herpes genitalis. It is typically spread by intimate sexual contact, including:

  • Vaginal sex
  • Oral sex
  • Anal sex
  • Hand-to-genitals contact
  • Contact with infected semen, vaginal fluid, or anal secretions
  • Shared sex toys

Despite its association with genital herpes, the rate of HSV-2 genital infections has been dropping in recent years as rates of HSV-1 genital infections appear to be increasing.

According to the Centers for Disease Control and Prevention (CDC), because the rate of HSV-1 oral herpes in the United States has been dropping, many people have no immunity to the virus and may only be exposed to it for the first time through oral sex.

While it is possible for HSV-2 to be passed to the mouth via oral sex, it is considered uncommon.

How Herpes Outbreaks Occur

Once HSV enters a cell, typically epithelial cells and keratinocytes of the skin, it begins the process of replication. While some people may experience symptoms at this stage, most do not.

During the initial (primary) infection, the virus is transported through nerve cells to branching points known as ganglia. There, the virus will stay in a latent state. Because it is not replicating, the virus is not recognized by the immune system.

On occasion, the virus will suddenly reactivate. When this happens, the virus will travel back through the nerve to the surface of the skin. This causes herpes blisters and sores in some people and no symptoms in others.

It is during this period of reactivation that the virus can be passed from person to person.

Once reactivation occurs, the immune system will kick in and bring the infection under control. With time, the virus will go back into hiding and return to its dormant state.

What Triggers a Recurrence?

Certain triggers can cause HSV to reactivate. This is known as a recurrence and can happen even if you have a healthy immune system.

Common triggers include:

  • An infection, illness, or injury
  • Emotional stress or anxiety
  • Exposure to ultraviolet (UV) radiation from the sun
  • Excessive heat or cold
  • Hormonal changes during periods
  • Fatigue

What Is the Risk of Herpes Recurrence?

Where HSV-2 differs dramatically from HSV-1 is that the majority of people who get an HSV-1 genital infection will experience recurrence. Studies suggest that roughly 80% of genital infections caused by HSV-2 will recur, compared to less than 20% caused by HSV-1.

Risk Factors for Getting Herpes

Herpes is a common virus, and there are a number of risk factors than can exponentially increase your risk of getting infected, including:

Risk Factors for Herpes Recurrence

Certain people are at greater risk of HSV recurrence, including more severe or frequent outbreaks. Chief among these are people with weakened immune systems.

When the immune system is suppressed or compromised, the body has fewer defenses when HSV reactivates. At the same time, the immune system will produce fewer proteins, called antibodies, that serve as sentinels against future outbreaks.

Risk factors for severe or frequent HSV recurrence include:

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. Genital herpes - CDC fact sheet (detailed).

  2. Bernstein DI, Bellamy AR, Hook EW, et al. Epidemiology, clinical presentation, and antibody response to primary infection with herpes simplex virus type 1 and type 2 in young womenClin Infect Dis. 2013;56(3):344–51. doi:10.1093/cid/cis891

  3. Government of Canada. Genital herpes guide: risk factors and clinical manifestations.

  4. New Zealand Herpes Foundation. Herpes myths vs facts.

  5. Sauerbrei A. Optimal management of genital herpes: current perspectives. Infect Drug Resist. 2016 Feb;2016:129-41. doi:10.2147/IDR.S96164

  6. American Academy of Dermatology. Herpes simplex

By Heather L. Brannon, MD
Heather L. Brannon, MD, is a family practice physician in Mauldin, South Carolina. She has been in practice for over 20 years.