One of the most common sexually transmitted diseases is herpes, which most people associate with “outbreaks” in the genitals. In actuality, most cases have no symptoms, and the majority of people with genital herpes don’t know they have it. Herpes simplex virus, which causes genital herpes, can also infect facial nerves around the mouth, and its “outbreaks” include blisters called cold sores.

A cold sore outbreak involves an “eruption” of blisters around the mouth, which slowly heal as the virus returns to dormancy. Most cold sores are caused by herpes simplex virus type 1, or HSV-1. Around 60 percent of Americans are infected with HSV-1, and most of these infections are oral, asymptomatic, and acquired in childhood through nonsexual contact. Despite how common this infection is, only 20 to 40 percent of us actually get cold sores — and an even smaller percentage experience cold sores more than once a year. The rest of us don’t get cold sores at all, even if we are infected with HSV-1. That’s one quirk about HSV — an infection is permanent and incurable, but most people never have symptoms!

The virus that causes oral herpes can also cause genital herpes.

Making matters more confusing, there’s a related virus called HSV-2, which most people associate with genital herpes. However, HSV-1 can also cause genital herpes, and anyone with an HSV-1 infection in the facial area has the potential to transmit the virus to a partner’s genitals while performing oral sex — whether or not cold sores are present. However, when HSV-1 strikes the genitals, the infection is usually milder, with fewer (if any) recurring outbreaks. Additionally, a previous HSV-1 infection in the facial area might make you more resistant to acquiring an HSV-1 infection in the genital area — but it doesn’t confer total immunity.

HSV-1 enters the body through a mucous membrane or a (possibly microscopic) tear in the skin. Just as a physical stimulus — like a fiery flame or a piercing needle — sends a message through a nerve to a cluster of neurons to be processed as a sensation, so too can HSV-1 use your nerve as a highway that transports it straight to its new home: a cluster (“ganglion”) of sensory neurons. An oral HSV-1 infection is headquartered in the trigeminal ganglion, which is a depot for the little nerves that fan out over the lower half of the face. Once it has invaded the trigeminal ganglion, HSV-1 sets up shop in the cells’ nuclei, integrating its DNA with your own before entering a period of dormancy. During this time, HSV-1 doesn’t cause any symptoms.

Sometimes, HSV-1 is “awakened,” at which time it replicates and travels back down a nerve to the face, where the virus can cause cold sores and start “shedding,” meaning that infectious virus particles are being produced. You can also “shed” without developing cold sores — which means you’re infectious but have no way of knowing it! The exact mechanism of this reactivation is mysterious, but it seems that many types of stimuli can trigger it:

physical or emotional stress

ultraviolet light (white snow reflects UV light, making skiers especially susceptible)

fever

immune suppression (which could result from HIV infection, chemotherapy, organ transplantation, etc.)

menstruation

facial trauma (e.g., surgery, fracture, or laser skin resurfacing)

colds

pneumococcal pneumonia

wind

X-ray irradiation

As HSV-1 reactivates, the sufferer might experience burning, itching, or tingling sensations, possibly preceding the outbreak by mere hours. Around three to five cold sores develop within a day or two, usually on the edge of the lips, and heal in eight to 10 days without scarring. If the sufferer experiences pain, it peaks at the beginning of the outbreak and goes away within five days. The virus retreats to the trigeminal ganglion and reestablishes dormancy.

Although one need not exhibit symptoms to be infectious, when cold sores are present the virus is most certainly being “shed.” Shedding is higher at the beginning of the outbreak, and viruses could originate from the blisters themselves or be present in saliva. If someone is suffering from a cold at the same time cold sores are present, viral shedding might increase by 3.5-fold. The amount of viral shedding might be influenced by what “triggered” the outbreak; for instance, the general population of HSV-1 sufferers shed less virus than people who are immunocompromised or those who have just undergone dental surgery.

People with recurrent cold sores can decrease risk of outbreaks by applying sunblock or a moisturized balm containing zinc oxide to their lips. They can also decrease risk of transmitting HSV-1 to others by:

washing used linens in boiling water

not sharing utensils, glasses, or similar items

abstaining from touching cold sores and then touching another person

not kissing or performing oral sex when cold sores are present

Unfortunately, because HSV-1 can be transmitted even in the absence of cold sores, you could still spread it to your partner at other times. Using latex condoms or dental dams decreases risk, but doesn’t eliminate it as HSV-1 spreads by skin-to-skin contact and latex barriers don’t cover the entire genital area. (Furthermore, lambskin condoms aren’t effective against HSV.)

When you have cold sores, you can reduce discomfort by applying an icepack or warm washcloth to them; avoiding hot drinks, spicy or salty foods, and citrus; gargling with cool water; and taking over-the-counter pain relievers. You can also try antiviral medications.

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 only tells 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.

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