Food additives are substances that become part of a food product when added (intentionally or unintentionally) during the processing or production of that food.

Food additives serve five main functions:

1. Maintain product consistency

Substances called emulsifiers provide a consistent texture and prevent products from separating. Stabilizers and thickeners provide an even texture. Anticaking agents allow substances to flow freely.

2. Improve or preserve the nutrient value

Many foods and drinks are fortified and enriched to improve the nutritional status of the United States population. For example, vitamins and minerals are added to many foods including flour, cereal, margarine, and milk. This helps to make up for vitamins or minerals that may be low or completely lacking in a person's diet. All products that contain added nutrients must be labeled.

3. Maintain the wholesomeness of foods

Contamination from bacteria can allow foodborne illnesses to occur. Preservatives reduce the spoilage that air, fungi, bacteria, or yeast can cause. Certain preservatives help preserve the flavor in baked goods by preventing the fats and oils from going bad. They also keep fresh fruits from turning brown when exposed to the air.

4. Control the acidity and alkalinity and provide leavening

Specific additives help change the acid-base balance of foods to obtain a desired taste, color, or flavor. Leavening agents that release acids when they are heated react with baking soda to help biscuits, cakes, and other baked goods rise.

5. Provide color and enhance flavor

Certain colors improve the appearance of foods. There are many spices and natural and synthetic flavors that bring out the best in the flavor of food.

Intentional or direct food additives are added to foods to produce a desired effect, such as to maintain freshness, improve nutritional quality, assist in processing or preparing food, or make a food more appealing.

Unintentional or indirect food additives are substances that are found in food during the production or the processing of a particular item. These are present in minimal quantities in the final product.

The U.S. Food and Drug Administration (FDA) has a list of food additives generally recognized as safe. Many have not undergone any testing, but they are regarded as safe by the scientific community. These substances are put on the GRAS list, which contains approximately 700 items. Examples of some of the items on this list are: guar gum, sugar, salt, and vinegar. The list is evaluated on an ongoing basis.

Safe is defined by Congress as "reasonable certainty that no harm will result from use" of an additive. Some substances that are found to be harmful to people or animals may be allowed, but only at the level of 1/100th of the amount that is considered harmful. This margin of safety is a protection for the consumer by limiting the intake of a dangerous substance. For example, some people are allergic to sulfites, and their reaction can be mild or very severe. People with any allergies or food intolerances should always check the ingredient listing (label) for their own protection.

The list of additives has been changed dramatically since the time the government began overseeing its safety. It is still important to gather information about the safety of food additives. The general public is encouraged to inform the FDA of any adverse reactions related to food or food additives.

The FDA and the United States Department of Agriculture (USDA) supervise and regulate the use of additives in products sold in the United States. However, people who have special diets or intolerances should be careful in selecting products in the grocery store.