Tetanus is usually caused by an infection with Clostridium tetani. As Clostridium tetani are anaerobic bacteria, they proliferate extensively in an oxygen-free environment. If a wound is small and shallow, and completely open to air, it is generally not susceptible to tetanus infection. However, if the wound is deep and the external opening is small, creating an anaerobic condition inside, it is easy to contract tetanus. Therefore, it is generally recommended to administer a tetanus antitoxin following an injury, as an internal infection with tetanus can lead to very serious conditions, potentially resulting in death.