Causes and Risk Factors of Herpes

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Herpes infections are caused by herpes simplex virus (HSV) types 1 and 2. These viruses are contagious, and they are 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. 

Common Causes

Herpes infections are caused by herpes simplex viruses, which 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 viruses can affect the areas that are typically associated with the other virus.  

There are also other herpes viruses, but they do not cause herpes. For example, chickenpox is caused by herpes zoster, and the common cold can be caused by Epstein-Barr virus, which is also a herpes virus.

Transmission

The herpes viruses spread when they come into contact with broken skin or with the mouth, vagina, penis, or anus. While herpes is most contagious when ulcers are open or oozing, it can also be spread when sores are not present and when the skin is perfectly intact due to what's known as asymptomatic shedding.

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. Common everyday activities are usually to blame for transmission (see below).

People can re-infect 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, rather than with a previous infection.

How HSV Causes Sores

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 the cells of your body 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 causing any symptoms.

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.

Recurrence

Certain triggers can cause the herpes virus to reactivate. This is known as a recurrence and can happen even if you have a normal immune system. There are a number of known triggers that can stimulate recurrence:

  • 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, 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.

  • 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, or of having frequent reactivations of your infection. Your immune system can be suppressed for a number of reasons, including an autoimmune condition, an immune system deficit, HIV, 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 a chemotherapeutic drug. 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 to certain activities:

    • 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 raises your risk. 
    • Kissing: Kissing or other mouth contact is one of the common ways of transmission of HSV-1. 
    • Sharing items: The HSV-1 virus can be transmitted by sharing items such as cups, mouthguards, toothbrushes, and even towels that have recently come in contact with 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.
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