Researchers at The University of Texas Medical School, in Houston, have identified family history as one reason why some people might be more susceptible to shingles, a severe skin condition. Their findings were published last year in an issue of Archives of Dermatology.

Shingles, or herpes zoster, is a burning, painful, itchy skin rash with blisters that can last up to five weeks and pain that can last months to years. Nearly 1 million shingles cases are diagnosed each year in the U.S.

The more relatives you have had who have experienced an outbreak of shingles, the higher your risk, says Dr. Stephen Tyring, clinical professor in the department of dermatology at the UT Medical School.

"If just one blood relative has had shingles, you should get vaccinated," he says. "Your risk is double that of someone who has had no relatives with the virus. The estimate, however, is most valid for first-degree relatives such as a mother, father, or sibling."

Researchers at The Center for Clinical Studies, an outpatient clinic in Houston, examined 1,027 patients treated between 1992 and 2005. Of the more than 500 patients with shingles, 39 percent reported knowing of a blood relative who had suffered from shingles. In contrast, only 11 percent of age, sex, race-matched patients who had never had shingles knew of any blood relative who had shingles in the past.

Shingles is caused by the same virus that causes chickenpox, the varicella-zoster virus. Patients must have had chickenpox to get an outbreak of shingles. The virus is not eliminated from the body after an episode of chickenpox has ended.

"The virus lies dormant in your system until you have an accident, dental work, physical or emotional stress, or your immune system is suppressed by a disease or virus. They can all be triggers that lead to a shingles outbreak," says Tyring, a co-author of the new study. Twenty percent of people who have had chickenpox will go on to have shingles.

People are less likely to get shingles if they have had the chickenpox vaccine, which was approved by the U.S. Food and Drug Administration in 1995.

Tyring, who was an investigator of the shingles vaccine, recommends the shingles vaccination for those with a family history. The shingles vaccine was approved for patients over 60 in 2006, and now is being studied in patients as young as 50 years of age.

In 25 percent to 50 percent of people older than 50, shingles pain can linger for months, or years, long after the rash and blisters have gone away—a condition called post-herpetic neuralgia.