Inhalation or respiratory anthrax is a life-threatening infectious disease caused by inhaling the spores of the bacterium Bacillus anthracis. 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, several toxins are released. Particles illustrated are not to scale.