Over time, baking powder becomes less effective as its rising components weaken. Signs that it needs replacement include an expired date on the packaging, a lack of fizz when mixed with warm water, dense and improperly risen baked goods, a bad smell indicating spoilage, and the importance of keeping it dry and sealed due to moisture weakening its power. When uncertain, switching to fresh baking powder ensures better baking outcomes. Regularly checking the date and doing tests maintain consistent baking success.