The researchers found that cold sore outbreaks are about 20 percent heritable. "That's very significant, but it means about 80 percent of the disease is due to other stuff. Do you ski without sunscreen on your lips? Are you prone to febrile illnesses? What strain of virus did you get?" Kriesel said.

They believe, he said, that the individual's own factors, the infection's viral load and similar factors and the environment all play a role in expression of the disease.

"We think that for people who get frequent reactivations, it's likely there are more than one susceptibility gene," Kriesel said.

They plan to do genotypings within the candidate genes to see what else they can learn about cold sores and genetics. Three of the six genes, in particular, look promising.

Co-authors, besides Hobbs and Kriesel, are Mark F. Leppert, Ph.D., distinguished professor and co-chairman of the Department of Human Genetics; Brandt B. Jones (B.S., senior research scientist), Division of Infectious Diseases; and Brith E.M. Otterud (B.S., computer professional), Department of Human Genetics.

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E-mail: lois@desnews.com