Drug allergies are the immune system's response to certain drugs. The symptoms that occur when there is a drug allergy may be confused with side effects that can cause the product itself. Among the most common symptoms of allergies are hives, itching of the skin and eyes, skin rash and swelling of lips, tongue and face. But if the allergy is aggravated can cause other more obvious symptoms of urgency, and even possible death, such as abdominal pain, confusion, diarrhoea, shortness of breath, dizziness, fainting, fast heartbeat, etc. In the case of allergies to sulfa drugs, so prevalent today by the widespread use of these drugs, the most common symptoms are fever and rash on genitals, face and trunk of the patient.