WEDNESDAY, Jan. 28 (HealthDay News) -- Stressful experiences can have a long-lasting impact on children's health, U.S. researchers report.

They evaluated the immune systems of teens who'd experienced either typical or extremely stressful childhoods, such as physical abuse or time in an orphanage. Specifically, the researchers looked at levels of antibodies against the common and usually latent herpes simplex virus type 1 (HSV-1).

The virus, found in about two-thirds of Americans, can cause cold sores and fever blisters. People with a healthy immune system can keep this virus under control and only develop symptoms when their immune system is compromised by stress or illness. But people with a weakened immune system may have trouble suppressing HSV-1 and produce antibodies against the activated virus.

The University of Wisconsin-Madison study found that teens who experienced physical abuse or stressful home environments as children had elevated levels of HSV-1 antibodies, an indication of a compromised immune system.

The findings, published in this week's online issue of the Proceedings of the National Academy of Sciences, suggest "that children's emotional environments are having widespread repercussions on their health," senior study author Seth Pollak, a professor of psychology and pediatrics, said in an university news release.

"Even though these children's environments have changed, physiologically they're still responding to stress. That can affect their learning and their behavior, and having a compromised immune system is going to affect these children's health," Pollak said.

"The immune system is not preset at birth," noted fellow author Chris Coe, a psychology professor and expert on the association between stress and immunity. "The cells are there, but how they will develop and how well they'll be regulated is very much influenced by your early environment and the type of rearing you have."

Related MedlinePlus Pages:

• Immune System and Disorders
• Stress