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Pictured above: A herpes simplex lesion on the lower lip on the second day after onset. Image: CDC Public Health Image Library ID# 5434

Herpes simplex virus is mystifying, fascinating, and sneaky. Mystifying because we have yet to unravel all of its secrets; fascinating because when we do uncover one of its mysteries, we are amazed by the capabilities of such a tiny, microscopic object; and sneaky because it enters our bodies by stealth and conceals itself in our cells, taking us by surprise when it comes out of hiding and causes outbreaks of blisters and other lesions.

It can also be confusing. Herpes simplex virus actually comes in two flavors: HSV-1 and HSV-2. HSV-1 is associated more with oral herpes, which can cause “cold sores,” a type of blister that appears on the lips or face. HSV-2 is associated more with genital herpes, which can cause blisters and other lesions in the genital area. It used to be standard to describe HSV-1 as an “above-the-waist” infection and HSV-2 as a “below-the-belt” infection — but now many researchers are pointing out that it’s more appropriate to say that HSV-1 is both an orally and genitally transmitted infection while HSV-2 is a predominantly genitally transmitted infection. If HSV-1 enters the body in the genital area, it can cause a genital herpes infection — and likewise, if HSV-2 enters the body in the facial area, it can cause an oral herpes infection.

Using condoms and dental dams during oral sex reduces risk of herpes transmission.

What exactly is a cold sore, anyway? A cold sore, also known as a fever blister, is a cluster of blisters that can pop up around the lips or even in the mouth. Sometimes, cold sores are so painful that eating or drinking is difficult, and in extreme cases sufferers must be treated for dehydration. An especially severe infection could also cause high fever or swollen lymph nodes, and in young adults a first oral HSV-1 infection might be misdiagnosed as tonsillitis, possibly leading to unnecessary tonsillectomies. Most symptomatic first-time cold-sore outbreaks occur during childhood, and take about two or three weeks to clear up. Luckily, the first infection is almost always the most severe, and when the infection is reactivated it usually happens without symptoms.

Because both cold sores and genital herpes are caused by herpes simplex viruses, and because oral herpes is so common, many people are concerned that they might be more vulnerable to acquiring a genital herpes infection than they previously thought. They might have a lot of questions, and if they’ve sought answers to those questions, they might have heard a lot of conflicting answers. Let’s see what the scientific literature has to say.

  • Can I get genital herpes if someone with cold sores performs oral sex on me?

Because HSV-1, the virus responsible for most oral herpes infections, can also cause genital herpes, many people wonder if someone with cold sores can transmit the virus to someone else by performing oral sex, resulting in a genital herpes infection. Other people wonder if HSV-1 can be transmitted via oral contact with the anus, resulting in a herpes infection in the rectal area. The answer to these questions is: Yes!

While HSV-1 only accounts for around 30 percent of genital herpes infections overall, many research teams are finding that HSV-1 is the predominant cause of genital herpes in some countries (such as Sweden) and in some U.S. populations, especially of younger females. For example, among students at a large Midwestern public university, researchers found that HSV-1 caused 31 percent of genital herpes cases in 1993 and grew to 78 percent in 2001. The increase was even more pronounced in females. This trend, in which HSV-1 infections in the genitals predominate over HSV-2, seems to be most common among younger people, women, and men who have sex with men. This change might be due to the fact that condom use for vaginal and anal intercourse is considered normal in most populations — while most people don’t use condoms or dental dams during oral sex, leaving them vulnerable to acquiring HSV-1 (and other infections!) from a partner.

This might sound like terrible news, since most of us are infected with HSV-1 and we might enjoy oral sex. But there is some good news. First of all, HSV-1 likes to live in the trigeminal ganglion — in the face. Because HSV-1 feels more at home in the trigeminal ganglion, an infection in that location is more likely to reactivate and cause cold sores periodically throughout a person’s life. When HSV-1 finds itself living in the sacral ganglion in the genital area, it doesn’t reactivate very often. So, if you are infected with HSV-1 in your genital area after receiving oral sex, recurrences will be uncommon and your infection will be milder than if you were infected with HSV-2, which is a related virus that is more strongly associated with genital herpes.

  • Can I be infected with HSV-2 in my facial area if I perform oral sex on someone with an HSV-2 infection in their genitals?

Just as HSV-1 can pass from the mouth to the genitals to cause a genital herpes infection, so too can HSV-2 pass from the genitals to the mouth to cause an oral herpes infection. However, oral HSV-2 infections aren’t as common as genital HSV-1 infections. Although there are some documented cases of oral HSV-2 infections, they aren’t very widespread. Furthermore, just as a genital HSV-1 infection is milder and less prone to recurrences than an HSV-2 infection in that area, so too is an oral HSV-2 infection milder and less prone to future outbreaks.

  • Can the virus be transmitted if someone isn’t showing any symptoms?

Unfortunately, just because someone lacks a telltale cold sore doesn’t mean they’re not infectious. It is quite possible for the virus to reactivate, not cause symptoms, but still “shed” from a carrier, at which point it can be transmitted to someone else — via skin-to-skin contact, saliva, or even tears. One large study, using a sensitive DNA amplifying technique called PCR, detected the asymptomatic shedding of HSV-1 on 33.3 percent of days. Another study of 50 people found that 90 percent of them had HSV-1 in their saliva at least once during a 30-day period.

Shedding patterns can be further influenced by what triggered the virus to reactivate — for example, higher-than-average amounts of virus are found in saliva samples from patients with oro-facial fractures.

  • If I’ve already been exposed to HSV-1 in my facial region, am I immune to reinfection in my genitals?

Some people think that already being orally infected with the cold sore virus makes them immune to HSV-1 infections in their genitals. It’s true that if you have an oral HSV-1 infection, you might have some degree of protection against acquiring HSV-1 infection in your genitals — but we don’t know to what degree a previous HSV-1 infection protects us from subsequent infections elsewhere in our bodies. More study is needed to answer this question more fully, but the short answer is that yes, reinfection in the genitals is possible.

  • Does a previous HSV-1 infection protect me from a subsequent HSV-2 infection?

As mentioned previously, most of us are orally infected with HSV-1 as children. Unfortunately, a preexisting HSV-1 infection doesn’t protect us from acquiring an HSV-2 infection later in life, though it’s possible that it will help mitigate symptoms of a first HSV-2 outbreak. Those who already have an HSV-1 infection are much less likely to experience symptoms upon an initial HSV-2 infection. Likewise, a previous HSV-2 infection does not protect someone from acquiring an HSV-1 infection. It’s possible for HSV-1 and HSV-2 to infect the genitals at the same time — it just might not be as likely.

  • Can my genital HSV-1 infection be transmitted to my partner’s genitals?

When HSV-1 infects the genitals, it usually got there as a result of oral sex. Because genital HSV-1 infections have fewer recurrences and are associated with less asymptomatic shedding, the genital-to-genital spread of HSV-1 is not as common.

If you want to find out if you’ve been infected with HSV-1 or HSV-2, you can get a blood test at a Planned Parenthood health center. This test will only tell you if you’ve been infected with either of these viruses, but in the absence of symptoms it won’t tell you where in your body the infections are located. We can also answer any questions you have about herpes and discuss antiviral medications with you.

Tags: safer sex, oral sex, herpes, condom, cold sores, sexually transmitted infections, genital herpes, STI, sexual health, STD Awareness, HSV, HSV-2

About Anna C.

Anna first volunteered for Planned Parenthood as a high school student in the 1990s. Since then, she has received a bachelor’s degree from UC Berkeley and a master's degree in epidemiology from the University of Arizona. As an ode to her fascination with microbes, she writes the monthly STD Awareness series, as well as other pieces focusing on health and medicine.