Here’s why that cold sore keeps coming back

For such a ubiquitous plague, cold sores can be mighty shaming.

In addition to the indignity of wearing a bulging, weepy blister on your lip, sufferers also must contend with the stigma of its source: HSV-1, a type of herpes simplex virus.

But unlike HSV-2, the virus that usually causes genital herpes, cold sores are not usually sexually transmitted (though they can be). Most people get infected with HSV-1 as kids, from kissy adults.

“It is one of the most common viral infections, and yet you’re a pariah,” said Dr. Adam Friedman, director of dermatologic research at Albert Einstein College of Medicine at Yeshiva University in New York. “People look at you like you’re a leper.”

About 70 percent of Americans are infected with HSV-1, but just a third of those infected have cold sore outbreaks, said Bryan Cullen, professor in the department of molecular genetics and microbiology at Duke University Medical Center. Genetics likely separates the lucky from the unlucky, he said.

The hardy virus, which stays in your body your whole life, survives by moving up the sensory nerves after initial infection and vacationing in nerve bundles, where immune cells can’t find and destroy it. Triggers such as stress, fatigue, sun exposure, picking at your lip or having a cold or the flu can reactivate some infected cells, which travel back to the initial infection site to cause a new outbreak.

There is no cure.

Though the virus is most contagious during an outbreak, when the virus is “shedding,” it’s also possible to transmit when no outbreak is visible.

Friedman recommends keeping your mouth away from others when you feel a cold sore coming, during the outbreak and for a few days after it goes away.

Taking prescription antivirals such as acyclovir (Zovirax) or valacyclovir (Valtrex) can reduce healing time or prevent a blister from forming at all, clinical trials have shown. It’s best to attack during the “prodrome” stage, when many people feel tingling or itching at the infection site, or have flulike symptoms.

Friedman suggests applying ice at the first hint of a cold sore, holding it against the infected site for no more than 15 minutes, to reduce swelling. You might also soak a cotton ball in whole milk and hold it against the sore for 10 to 15 minutes daily. Milk contains the protein monocaprin, which can halt HSV-1.

Finally, cover a blister with a thick emollient such as petroleum jelly to speed healing and protect the wound from bacteria.