Causes and Risk Factors

Caused By A Virus

Shingles is caused by a germ called varicella-zoster virus -- the one that gave you chickenpox when you were a child. As you recovered from chickenpox, the sores healed and the other symptoms went away, but the virus remained. It is with you for life.

The virus hides out in nerve cells, usually in the spine. But it can become active again. Somehow, the virus gets a signal that your immunity has become weakened. This triggers the reactivation.

When the virus becomes active again, it follows a nerve path called a dermatome. The nerve path begins at specific points in the spine, continues around one side of the body, and surfaces at the nerve endings in the skin. The pattern of the rash reflects the location of that nerve path.

Risk Factors

The leading risk factor for shingles is a history of having had chickenpox. One out of every five people who have had chickenpox is likely to get shingles.

Another risk factor is aging. As we age, our natural immunity gradually loses its ability to protect against infection. The shingles virus can take advantage of this and become active again.

Conditions that weaken the immune system can also put people at risk for shingles. Shingles is especially dangerous for anyone who has had cancer, radiation treatments for cancer, HIV/AIDS, or a transplant operation.

Most cases of shingles occur in adults. Only about 5 percent of cases occur in children. With children, immune deficiency is the primary risk factor, but children who had chickenpox before they were one year old may also get shingles before they become adults.

There have been studies of adults who had chickenpox as children and were later exposed to children who had chickenpox. Interestingly, that exposure apparently boosted the adult's immunity, which actually helped them avoid getting shingles later in life.

Stress is another factor that may contribute to outbreaks. While stress alone does not cause the outbreaks, shingles often occurs in people who have recently had a stressful event in their lives.