A preservative is a substance added to products, particularly food, cosmetics, and pharmaceuticals, to prevent spoilage, decay, or contamination by microorganisms. It helps extend the shelf life of products by inhibiting the growth of bacteria, mold, and yeast. Preservatives can be natural, like salt and vinegar, or synthetic, such as sodium benzoate and potassium sorbate. Their use is essential for maintaining safety and quality in various consumer goods.