A drug allergy is an abnormal reaction of the immune system to a medication. When a person with a drug allergy takes a specific drug, their body mistakenly identifies it as a harmful substance, leading to symptoms such as rashes, itching, or swelling. In severe cases, it can cause anaphylaxis, a life-threatening reaction that requires immediate medical attention. Common medications that can cause drug allergies include antibiotics like penicillin, nonsteroidal anti-inflammatory drugs (NSAIDs), and certain vaccines. It is important for individuals to inform their healthcare providers about any known drug allergies to avoid potentially dangerous reactions in the future.