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Ancient people knew that some kinds of clay had healing qualities. They put clay on their skin to cover wounds. They also used the natural rock or soil material to treat stomach problems. Now, American researchers may have discovered how some clays work as a medicine that could fight some infections. Blue clays are found in volcanic areas of the world. Lynda Williams is a clay and mineral scientist at Arizona State University in Tempe. She and her research team found the clay was effective against some pathogens. Pathogens are bacteria and viruses that cause disease. In laboratory tests, they saw how a blue-colored clay is effective against MRSA. MRSA is a sometimes deadly bacterial infection that does not respond to antibiotics. The clay was also effective in treating Buruli ulcer, a skin disease found in the Ivory Coast. Here is how the blue clay works against bacteria. The clay contains iron and aluminum and these minerals work together. Lynda Williams says aluminum lets iron flood into the harmful bacteria. The iron oxidizes, or mixes with oxygen and then kills the bacteria. Williams says she hopes the study will interest drug companies that want to explore the healing properties of blue clays. The National Science Foundation provided financial support for the study. Williams and her team reported their findings in the journal Nature Scientific Reports.