A dairy allergy occurs when the immune system mistakenly identifies proteins in milk as harmful. This can lead to various symptoms, including hives, stomach pain, and difficulty breathing. The most common proteins that trigger these reactions are casein and whey. People with a dairy allergy must avoid all products containing milk, including cheese, yogurt, and butter. It's important to read food labels carefully, as dairy can be hidden in many processed foods. In severe cases, exposure to dairy can lead to anaphylaxis, a life-threatening reaction that requires immediate medical attention.