) and said it could form the basis for new drugs. "Our observations show that human skin contains a chemical shield," they wrote in a letter to the science journal Nature. "Disruption of this shield, as in cystic fibrosis, might be a reason for recurrent infections of skin," they added. They found the antibiotic while investigating why people with psoriasis, which causes itching and flaking, did not have more skin infections. Tests showed the antibiotic was very effective against common bacteria like E coli -- one strain of which causes food poisoning -- and the infectious yeast Candida albicans. It was less effective against staphylococcus bacteria, which naturally live on the skin and which can sometimes cause fatal infections. One other "natural" antibiotic has been found in the body. Known as hBD-1, it is found in the bladder, genitals and lungs. Perhaps resistance-free antibiotics could be developed based on hBD-2, they said.