A preservative is a substance added to food, medicine, or other products to keep them from spoiling or decaying. Without preservatives, bread would grow moldy within days, and many medicines would become unsafe to use long before reaching patients who need them.

Think about a loaf of bread from a bakery versus one from the grocery store. The bakery bread might last only a few days before mold appears, while the store-bought bread stays fresh for weeks. That difference often comes from preservatives, which slow down the growth of bacteria, mold, and yeast that cause food to rot.

Some preservatives occur naturally: salt has preserved meat and fish for a long time, and sugar preserves jams and jellies. Vinegar, another natural preservative, keeps pickles crisp and safe to eat for months. Other preservatives are manufactured chemicals designed to do the same job efficiently.

Museums use preservatives to protect artifacts and documents from decay, helping objects survive for future generations to study and enjoy. Wood preservatives keep lumber from rotting when exposed to the weather. The word can also describe anything that helps maintain or protect something valuable: some people view libraries as preservatives of knowledge and culture.