Tomato sauce should be kept in the fridge after opening it to preserve the quality and flavor and prevent spoilage.
Once opened tomato sauce requires refrigeration to prevent mold growth and spoilage and should be used within 5 to 7 days of refrigeration.
If unopened tomato sauce can remain at room temperature but once opened it always requires refrigeration.
When tomato sauce goes bad the tomato sauce will start to smell bad, sour or rotten.
The bad tomato sauce will also grow mold and taste off or sour.
Or if the container of tomato sauce is leaking, bulging, swollen, damaged or cracked the tomato sauce could be contaminated and it should be thrown out.
If the tomato sauce has a change in color it should be thrown away.
As long as the tomato sauce is sealed and not opened it can remain in your pantry without refrigeration until ready to use.
But once opened it needs to be refrigerated.