Causes and Risk Factors of Herpes

Herpes infections are caused by herpes simplex virus (HSV) types 1 and 2. These viruses are contagious and transmitted from one person to another through skin-to-skin contact. Kissing or touching is the main cause of HSV-1 transmission, and sexual contact is the main cause of HSV-2 transmission. 

herpes causes and risk factors
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Common Causes

Herpes simplex viruses enter through the skin and travel to the nerves, where they generally do not cause problems. Herpes can cause skin sores, however, when the viruses become active.

HSV-1 is normally associated with infections on or around the mouth and lips, and HSV-2 is usually associated with genital infections.

Other locations in the body, such as the eyes or neck, can also be affected. Each of the two herpes viruses can affect the areas that are typically associated with the other virus.

There also are other herpes viruses, though they aren't associated with these issues. For example, chicken pox is caused by herpes zoster. Infectious mononucleosis (mono) is caused by Epstein-Barr, which is also a herpes virus.


The herpes viruses spread when they come in contact with broken skin or with the mouth, vagina, penis, or anus.

While herpes is most contagious when open sores known as ulcers are open or oozing, it can also be spread when sores are not present and when the skin is intact due to what's known as asymptomatic shedding. In other words, the virus is there and can be passed even though there's no obvious sign of it.

Unfortunately, there is no way to detect asymptomatic shedding, so you have to consider herpes contagious all the time, even in the absence of symptoms.

People can reinfect themselves by touching a sore and then scratching or rubbing another area of skin on their own body.

Women who have vaginal HSV-2 infections can also transmit the virus to their babies during vaginal delivery. This type of transmission is more common if the mother has newly acquired the infection.

Infection and Reactivation

Once it enters a human cell, the HSV virus penetrates the cell's nucleus and begins the process of replication. At this stage, even though cells may be infected, you probably will not experience any symptoms.

During the initial infection, the virus is transported through nerve cells to nerve-branching points, known as ganglia. It is there that the virus will stay in an inactive, dormant state, neither replicating nor presenting any signs that it's even there.

On occasion, the dormant virus may suddenly reactivate, starting the replication process anew. When this happens, the virus will travel back through the nerve to the surface of the skin. With this, many of the infected skin cells are killed, causing blisters to form. The eruption of these blisters creates the characteristic ulcers that are recognized as cold sores or genital herpes.

What Triggers Recurrence

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

There are several known triggers that can stimulate recurrence, including:

  • Physical stress, such as an infection, an illness, or an injury
  • Persistent emotional stress or anxiety for greater than one week
  • Exposure to ultraviolet light (UV light, such as from the sun), excessive heat, or cold
  • Hormonal changes, such as during menstruation
  • Fatigue

Health Risk Factors

There are a number of health factors that can predispose you to have a more severe or longer-lasting HSV infection if you already have HSV-1 or HSV-2. These risk factors do not make you more likely to acquire the infection, however. They are:

  • Immunosuppression: If your immune system is deficient for any reason, you are at a greater risk of having a more serious or persistent HSV infection, as well as more frequent reactivations. Your immune system can be suppressed for several reasons, including an autoimmune condition, human immunodeficiency virus (HIV), immunoglobulin A (IgA) disease, an illness such as cancer of the bone marrow, chemotherapy treatment, or organ transplantation.
  • Immunosuppressive medication use: You can have a worse HSV-1 or HSV-2 infection or a reactivation if you are on an immunosuppressive medication such as a steroid or chemotherapy. This should no longer be the case once you stop taking the medication and your immune system function returns to normal.
  • HIV: HIV infection specifically causes decreased immunity to viruses, and herpes virus infections may be more severe if you have HIV infection. 
  • IgA deficiency: While any immune deficiency can predispose you to recurrent sores or to a more severe bout of HSV infection, IgA deficiency is the immune deficiency most often associated with HSV. IgA is an immune protein that specifically protects against infections of the mucous membranes, which are the areas of thin skin that are protected by a fluid-like mucus, such as the mouth and vagina. 

Lifestyle Risk Factors

Herpes is a particularly common virus, and there is an especially high risk of exposure associated with certain activities, including:

  • Unprotected sex: HSV-2 is most often transmitted from one person to another through sex, including oral sex. HSV-1 can also be transmitted through sexual activity, although it is not as common. Having multiple sexual partners and having unprotected sex with partners who could be infected raise your risk. 
  • Kissing: Kissing or other mouth contact is one of the most common ways of transmission of HSV-1. 
  • Sharing items: The HSV-1 virus can be transmitted by sharing items such as cups, toothbrushes, and even towels that have recently been exposed to the virus. Using someone else's lipstick, lip gloss, or lip balm is particularly problematic, as these items are inherently moist, which allows the virus to easily stick around.
  • Prolonged skin-to-skin contact: Herpes gladiatorum, a type of infection caused by HSV-1, is characterized by sores on the face, head, and neck. This type of herpes infection is most often noted among wrestlers.

Frequently Asked Questions

  • Is HSV-1 an STI?

    HSV-1 is not classified as a sexually transmitted infection (STI). Though it can be spread through sexual contact, this is not the most common method of transmission. In fact, oral herpes is often contracted during childhood due to direct contact with sores (for example, a parent giving their child a kiss) or items that are contaminated.

  • Do cold sores mean you have an STD?

    Not necessarily. Cold sores (oral herpes) are typically caused by HSV-1, which is usually spread through nonsexual contact. HSV-2—the sexually transmitted variant—can appear in or around the mouth if contracted through oral sex. However, it is rare that a cold sore is due to HSV-2.

  • Can you get herpes from stress?

    No, but if the virus is dormant in your body, stress can trigger an outbreak. It is possible to contract HSV-2 without having any noticeable symptoms and remain asymptomatic for many years. 

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2 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. American Academy of Dermatology. Herpes simplex

  2. Centers for Disease Control and Prevention. Genital herpes - CDC fact sheet (detailed). Reviewed July 22, 2021.

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