A tuberculosis skin test involves injecting a tiny quantity of inactivated tubercle bacteria into the skin. A positive result becomes apparent at the injection site after 48 hours, characterized by swelling accompanied by a pink area. This signifies that the patient has had a past tuberculous infection, but, unless it’s a small child, it does not confirm that the infection is currently active. Conversely, a negative test indicates no skin reaction and suggests that the patient is not currently affected by tuberculosis.