The first sign that red cabbage is bad is its black spots. While these aren’t always pathogens, they can be bacterial or fungal growth signs. Depending on the type, these marks can be humorous or dangerous. If you notice that the leaves of your cabbage are dangling, you’ll need to discard the whole thing. Fortunately, it’s easy to spot the signs of rotting cabbage. When buying red cabbage, remember that it’s best to wash it well to avoid bacteria. The more mature a cabbage is, the less likely it is to be dangerous to your health.