How Contagious Is HSV-1 Genitally?

The virus that causes cold sores—herpes simplex virus type 1 (HSV-1)—also causes a third of genital herpes cases. HSV-1 is contagious and can be passed orally and genitally, either from mouth to mouth, genitals to genitals, mouth to genitals, or genitals to mouth.

That means that you can get genital herpes if someone with a cold sore performs oral sex on you. And, that's a concern given that nearly half of the U.S. population has HSV-1, according to the Centers for Disease Control and Prevention (CDC).

This article explains how you can get genital herpes from a cold sore and vice versa. It also details how herpes can spread through oral sex and offers tips to prevent herpes transmission.

What Are Cold Sores?

A cold sore (herpes labialis) is a cluster of tiny fluid-filled blisters that usually form on one side of the lips. Most people can tell when a cold sore is coming on: The area will feel tingly or itchy just before the lesion pops up. These sensations are known as prodromal symptoms.

Cold sores break open easily. When they do, the clear fluid inside oozes out and the blister forms a crust. Most blisters go away after a week or two.

What Is Genital Herpes?

Genital herpes (herpes genitalis) lesions are clusters of blisters that may be preceded by pain or tingling. Lesions can form on or inside the vagina, on the penis or scrotum, and around the anus, thighs, or buttocks.

Can HSV-1 Spread Genitally?

Cold sores and genital herpes are both caused by a herpes simplex virus. Most cold sores are caused by herpes simplex 1 (HSV-1), while genital herpes is most often caused by herpes simplex 2 (HSV-2).

It is well established that HSV-1 is far more prevalent than HSV-2 (47.8% versus 11.9% respectively), and it is not uncommon for children to have cold sores.

Genital herpes is diagnosed in adults, or adolescents, who are sexually active through direct contact with the genitals. People assigned female at birth are more susceptible to contracting genital herpes and are twice as likely to have HSV-2 than people assigned male at birth.

However, sometimes genital herpes infections can be caused by HSV-1. This infection on the lips of one person can spread to the genitals of another person during oral sex, causing an HSV-1 infection.

In fact, some scientists estimate that more than half of new genital herpes infections are caused by HSV-1 rather than HSV-2.

Although not nearly as common, it is also possible for a genital HSV-2 infection to be transmitted to a person's mouth—in other words, you could develop a cold sore if you perform oral sex on someone with genital herpes.

It's important to be aware that both cold sores and genital herpes can be transmitted from one person to another even when there are no obvious lesions. This is known as asymptomatic shedding.

Symptoms of Oral and Genital Herpes

Both oral herpes and genital herpes are characterized by the outbreak of painful blisters that rupture, leaving an open, concave sore (ulcer).

Both progress in similar ways:

• There may be initial redness, swelling, burning, pain, or itching around the site of an impending eruption. Some people may also experience fatigue or mild flu-like symptoms.
• Painful, fluid-filled blisters will develop rapidly in a tight cluster, rapidly increasing in size and often converging into larger blisters.
• The blisters will typically rupture, leaking fluid and forming a painful ulcer.
• The sore will start to crust over and heal over a period of days or weeks.

Oral herpes tends to heal in four to six days. Genital herpes can take anywhere from one to three weeks to fully heal.

How Is Genital Herpes Treated?

Genital herpes is treated with antiviral drugs which don't cure the disease but may reduce the severity or duration of the infection if started early (ideally within the first 24 hours of the appearance of symptoms).

There are three antivirals approved for the treatment of genital herpes:

• Zovirax (acyclovir): Taken in a 400-milligram (mg) dose three times daily for seven to 10 days
• Famvir (famciclovir): Taken in a 250-mg dose three times daily for seven to 10 days
• Valtrex (valacyclovir): Taken in a 1,000-mg (1 gram) dose twice daily for seven to 10 days

If there are frequent recurrences, your healthcare provider may prescribe Zovirax, Famvir, or Valtrex in a low dose to be taken once daily (a practice known as herpes prophylaxis). Doing so may significantly reduce the risk of repeated outbreaks while lowering your risk of passing the virus to others.

Possible Complications

For most people, genital herpes is a self-limiting infection that poses no long-term harm.

But for people with compromised immune symptoms, such as those with advanced untreated HIV, the virus can sometimes disseminate (spread) to other parts of the body, causing potentially life-threatening complications like:

• Meningitis: Inflammation of the tissues that surround the brain and spinal cord
• Encephalitis: Inflammation of the brain
• Esophagitis: Inflammation of the esophagus (feeding tube)
• Hepatitis: Inflammation of the liver
• Liver failure: Particularly during pregnancy, increasing the risk of maternal and fetal death

Genital herpes also increases the risk of getting HIV. This is not only because the open ulcer allows HIV easier access into the body but also because the infection draws the very immune cells (called CD4 T-cells) that HIV targets for infection.

How Is Genital Herpes Diagnosed?

In most cases, genital herpes can be diagnosed based on the appearance of the characteristic lesions. If there is any doubt about the diagnosis, a swab of fluid from the sore can be sent to the lab for positive confirmation using a genetic test called polymerase chain reaction (PCR).

There are also blood tests that can differentiate between infection by HSV-1 and HSV-2 based on immune proteins, called antibodies, produced n response to the viruses. The test may not be necessary given that the differentiation won't alter the course of treatment for a first outbreak.

Where the tests may be useful is when there is a recurrence of genital herpes. Because HSV-1 is less likely to cause recur over the long term compared to HSV-2, the differentiation can help determine whether herpes prophylaxis is needed.

The blood test may also be useful in detecting if the person's partner has herpes. If the partner is uninfected (or does not have the same type of herpes), the findings can support the case for starting herpes prophylaxis.

How to Prevent Genital Herpes

The same measures that help prevent a herpes infection during genital-to-genital contact can help prevent infection of the genitals from a cold sore, including the following:

Abstain

If your partner has a cold sore, the only way to guarantee you won't get infected is to avoid oral sex until the lesion has cleared up completely.

Someone with a cold sore can pass herpes to you, which means you can pass it back to them. Prevention is key, so it's best not to kiss or share a toothbrush, coffee cup, water bottle, or eating utensils.

Use a Condom

An external condom that goes on a penis will not completely eliminate the risk of spreading the herpes virus from a cold sore to another person's genitals. Neither will an internal condom placed into an anus or vagina. But they will provide some protection when used correctly.

Make sure the condom you use is approved by the Food and Drug Administration (FDA) for protection against sexually transmitted infections (STIs).

Get Tested

Herpes testing isn't a standard part of sexual health care. However, if you believe you've been exposed to herpes and want to know what your status is, ask a healthcare provider for a test.

You may also want to be tested if you're at risk for a herpes infection. You could be if you:

• Do not use a condom (or use it improperly)
• Have a partner with human immunodeficiency virus (HIV) and/or another STI since having HSV-2 increases your risk of becoming infected with other STIs
• Have had sex with someone who has herpes
• Have lesions that look like herpes on any part of your body
• Have multiple sex partners
  

Testing may involve swabbing fluid and cells from a lesion or taking a sample of blood from a vein. Both types of samples are then tested for the virus in a lab.

Some blood tests are designed to identify specific types of herpes virus, but they are not 100% accurate. 

Summary

Cold sores and genital herpes are both caused by herpes viruses. Cold sores most often are associated with HSV-1 while genital herpes is associated with HSV-2. However, HSV-1 can be transmitted from one person's mouth to another person's genitals during oral sex. Prevention steps include abstaining from oral sex, using condoms, and taking medication to suppress the herpes virus.