The PPD skin test, generally known as the PPD skin test, is a way to test for Mycobacterium tuberculosis infection, and a hard nodule that does not go away for a long time does not indicate a tuberculosis infection. The PPD skin test is a test that can help the body diagnose as well as differential diagnosis of tuberculosis. However, whether the nodules subside or not is not a criterion for determining the presence of tuberculosis infection, and there is no absolute correlation between the size of the nodules and the occurrence of tuberculosis infection. The PPD skin test itself cannot confirm tuberculosis infection, and can only be used as a reference indicator in clinical practice. Even if a positive result is obtained, it can only mean that one has been infected with tuberculosis, and it may be an immune response to BCG vaccination. Therefore, whether the nodules subside or not is not necessarily related to the occurrence of tuberculosis infection. In conclusion, the result of PPD skin test can only be used as a reference and cannot confirm the diagnosis of TB infection. Therefore, the fact that the nodules do not go away after the test has no special significance for the occurrence of TB infection, and naturally, it does not indicate whether TB infection has occurred or not. Individuals with nodules that do not go away after the PPD skin test, but with no other discomfort, should not be overly concerned.