Tetanus is caused by the bacterium Clostridium tetani, which typically enters the body through puncture wounds, cuts, burns, or other breaches in the skin. Once inside, the bacteria produce a potent neurotoxin that affects the nervous system, leading to muscle stiffness, spasms, and potentially life-threatening complications such as respiratory failure. The infection is not contagious and cannot spread from person to person. Prompt wound care, vaccination, and early medical intervention are critical to prevent the toxin from causing severe systemic effects.