Butter can be left at room temperature for a short time, but a week is too long, especially in warm conditions. Salted butter lasts longer, while unsalted butter spoils faster. Left-out butter can develop bacteria, mold, or become rancid, leading to unpleasant flavors or foodborne illness.

Experts recommend storing butter in the fridge and only taking out what’s needed. If you’re unsure about butter left out for a week, it’s safer to discard it and use fresh butter or a substitute like margarine. Always store butter covered to extend its freshness.