You should not get wet until 72 hours after the TB skin test. This is because the results are observed for 48-72 hours after the TB skin test. Tuberculosis skin test, also called tuberculin test, also called PPD test, is to inject tuberculin into the skin and observe the changes in the skin within 48-72 hours. If the skin does not show nodules, or if the diameter of the nodules is very small, under 0.5cm, it is considered negative. If the diameter is between 0.5-2cm, it is positive. If the diameter is more than 2cm, it is strongly positive. Strong positives help in the diagnosis of active TB, and if they are strong positives, the sputum should be examined further for sputum testing, and imaging tests should also be done. If both tests support it, the diagnosis of active TB is confirmed.