Anthrax is a disease caused by the bacterium Bacillus anthracis. It primarily affects animals, but can also infect humans if they come into contact with infected animals or contaminated materials. Anthrax has three forms: cutaneous (skin), inhalational (breathing), and gastrointestinal (digestion). The most common form is cutaneous anthrax, which occurs when the bacteria enter the body through a break in the skin. Inhalational anthrax is rare but can be deadly if not treated promptly. It occurs when the bacteria are inhaled and reach the lungs, where they multiply and spread throughout the body. Gastrointestinal anthrax happens when an individual consumes contaminated food or water containing the bacterium. This form is also rare but can be fatal if left untreated.