The tuberculosis skin test, also known as the tuberculin test or PPD test, should not be touched with water after the skin test because it will affect the results of the skin test and cause the results to be different from the actual results. Water can be touched after 72 hours of the TB skin test and will no longer affect the results. The tuberculin test is an important ancillary test for the diagnosis of tuberculosis, which is performed by subcutaneously injecting tuberculin and observing the changes at the skin test site. If there is no redness or hard nodules at the site, tuberculosis can be ruled out. However, this test cannot confirm the diagnosis of tuberculosis, but needs to be combined with the patient’s symptoms, lung imaging, sputum Mycobacterium tuberculosis smear and other tests to make the diagnosis.