You should not take a shower temporarily after the TB skin test, but you can take a shower after 3 days. This is because the TB test requires 48-72 hours to observe the results, so if you take a shower, it will affect the observation of the results. The TB skin test, also known as the tuberculin test or PPD test, involves injecting tuberculin toxin into the skin and observing changes in the skin 48-72 hours later. The test is negative if there is only redness and no nodules, or if the nodules are small and the diameter of the nodules is <0.5 cm. If the diameter of the nodule is >0.5 cm and less than 2 cm, it is positive. If the nodule is >2 cm in diameter, it is strongly positive. A strong positive test is helpful in the diagnosis of active tuberculosis. A positive test indicates that the patient is infected with Mycobacterium tuberculosis, while a negative test indicates that the patient is not infected with Mycobacterium tuberculosis and requires vaccination.