Cutaneous anthrax is an infection of the skin caused by the bacterium Bacillus anthracis. The bacteria causes disease when it comes into contact with non-intact skin. During an infection, an initial skin lesion forms then blisters. The blister breaks down into a black ulcer and nearby lymph nodes may become infected and painful. A scar is often formed which then dries and falls off within two weeks. In 20% of untreated individuals, the infection may spread to the bloodstream and become fatal. Although with proper treatment, death is extremely rare.

Inhaled anthrax is particularly deadly. Although the spores are dormant when breathed in, they germinate when exposed to a warm, moist environment, such as the lungs. Not all particles are small enough to pass into the alveoli, or air sacs, but those that do begin to multiply and may spread to the lymphatic system. When the spores germinate in the lymph nodes, several toxins are released. Particles illustrated are not to scale.

Bacillus anthracis is an aerobic spore-forming bacterium that causes disease in humans and animals. The bacteria is found in two forms cutaneous anthrax and inhalation anthrax. Cutaneous anthrax is an infection of the skin caused by direct contact with the bacterium. Inhalation or respiratory anthrax is an infectious disease caused by inhaling the spores of the bacterium. While anthrax commonly affects hoofed animals such as sheep and goats, humans may acquire this disease as well. Anthrax is a potential agent for use as a biological weapon or bio-terrorism.