Old tuberculosis foci, which are traces of treated or untreated lungs, are generally not contagious. However, when there are still resting tuberculosis bacilli inside the old tuberculosis foci, they will be resurrected when the immunity of the body decreases and re-infection occurs, which means that the old tuberculosis flares up again, and in this case the conditions with expelled tuberculosis bacilli will be infectious. Therefore, when there are old tuberculosis foci in the lungs, there is no problem if there is no change in the size of a calcified foci in the body every time there is a physical examination. However, some of the old tuberculosis is cavity-like changes or not completely calcified, and there may be tuberculosis bacteria in it, and when the immunity of the body decreases, tuberculosis infection will occur again.