Is it safe to leave homemade tomato sauce on the stove for days?

No, it is not safe to leave homemade tomato sauce on the stove for days. When you cook the tomato sauce, you're eliminating or killing potentially harmful bacteria that could cause foodborne illnesses. However, if you leave it out on the stove, the surviving bacteria can multiply very quickly to an unsafe level, particularly in the "danger zone" of 40°F (4.4°C) to 140°F (60°C) and potentially cause food poisoning. If you cook the sauce in advance, it is best to let it cool down to room temperature for about 30 minutes, then store it in the refrigerator or freezer as soon as possible.