An unexplained and sometimes debilitating disease that causes oozing sores and fibers to grow from patients' skin doesn't come from a mysterious bug or virus, federal researchers reported Wednesday. The disease is all in the mind.

Morgellons disease, a skin disorder, was first described 300 years ago, but an outbreak in 2008 across the South prompted U.S. Sen. Dianne Feinstein, D-Calif. to request a study to look into the disease's cause.

Results from the $600,000 federal investigation were reported Wednesday in the online journal PLoS ONE.

We found no infectious cause, Mark Eberhard, an official with the Centers for Disease Control and Prevention and member of the study team, told The Associated Press.

Sufferers of Morgellons (mor-GELL-uns) cite a variety of symptoms including crawling sensations along their skin, fatigue, erupting sores and fibers of red, blue or black that sprout from their open wounds.

Though the disease was first mentioned in a 1674 medical paper that described similar symptoms, researchers named the disease in 2002.

Though patients say the disease is real, research has come to the opposite conclusion, prompting some doctors to label the condition delusional parasitosis.

One hundred and eight Morgellons patients didn't exhibit any physical disease, according to a study from the Mayo clinic in May 2010. Instead, the study found the skin problems came from patients scratching and picking at their skin.

The CDC study broadened the initial study and allowed researchers to determine the frequency of the disease.

Across 13 counties in northern California, researchers found 115 residents who had Morgellons symptoms through health insurance provider Kaiser Permanente of Northern California.

Most Morgellons patients were middle-aged women who were not found in a geographic cluster, The Associated Press reported.

The disease condition was found in four out of 100,000 Kaiser enrollees, the study found. Of the 115 residents, 40 allowed researchers to conduct a battery of physical and psychological tests.

Researchers also took fibers from 12 patients and specialists at the Armed Forces Institute of Pathology concluded that the mystery material was cotton and nylon.

However, the researchers caution that their study isn't the final word on the disorder that clearly irritates patients.

The absence of evidence is not evidence of absence, Felicia Goldstein, an Emory University neurology professor and study co-author, told The Associated Press.

Randy Wymore, an Oklahoma State University pharmacologist, has concluded for years that Morgellons is a physical, not a psychiatric, disorder.

Wymore, who hadn't seen the CDC paper, questioned how the Kaiser doctors had handled Morgellons patients in the past and how that might have influenced the study.

There is always the question: How many of the study participants actually have Morgellons Disease? he wrote The Associated Press in an email.