TB is spread primarily from person to person through infected air during close contact. The bacteria get into the air when someone infected with TB of the lung coughs, sneezes, shouts, or spits. A person can become infected when they inhale minute particles of the infected sputum from the air. It is not possible to get TB by just touching the clothes or shaking the hand of someone who is infected.

TB germs spread more easily in crowded conditions as the bacteria sometimes stay alive in the air for a few hours, especially in small closed places with no fresh air. Fresh air scatters the germs and sunlight acts as a bactericide, killing the TB organisms. Exposure to moderately hot temperatures for extended periods of time is sufficient to kill these bacteria. Extra-pulmonary TB does not spread from person to person.