Anthrax infection of the skin. The most common form of anthrax, cutaneous anthrax starts as a red-brown raised spot that enlarges and has redness, blistering, and hardening in the area of the spot. The center of the spot then shows an ulcer crater with blood-tinged drainage and the formation of a black crust (an eschar). The glands in the area become swollen (enlarged lymph nodes), and the patient may have muscle aching and pain, headache, fever, nausea, and vomiting.