Acid erodes tooth enamel, so the less you have touching your teeth the better. Consuming sugar and starches starts production of digestive acids in your mouth, and foods with already high acid content (like citrus fruit or soda) bring acid to your teeth directly. When you're eating or drinking foods high in acid, starch or sugar, use a straw if possible and brush your teeth right after. This will lessen the time these substances spend on your teeth.
Over-the-counter mouthwashes also contain acid. If you're unsure about mouthwash ingredients, ask your dentist to recommend a brand. Eating foods, such as milk or cheese, can help neutralize acid introduced to the mouth [source: WebMD].