What is TB? TB is usually an infection of the lungs. It is spread by sharing air with someone who is suffering from TB disease. If you are healthy, your body puts the TB germs to sleep. The germs are kept asleep forever unless your body becomes weak with age, disease or medical treatments. If the TB germs wake up, they can start to do damage to the body. When the damage starts, then you may have symptoms and spread the germs to others.