Anthrax are bacteria that live in the soil. They form spores, which can be inactive for a long time. When active, anthrax form new bacteria. Naturally occurring anthrax infections usually begin when the bacteria enter through a cut or scrape. A raised itchy bump develops, which looks like an insect bite. After a day or 2, a blister forms. This is followed by a painless open sore, which is usually 1 to 3 cm or roughly an inch or smaller in diameter, with a black area in the center. Antibiotics are used to treat anthrax infections of the skin.