Anaphylaxis is a severe, potentially life-threatening allergic reaction that can develop rapidly. It is also known as anaphylactic shock. Signs of anaphylaxis include: itchy skin or a raised, red skin rash swollen eyes, lips, hands and feet feeling lightheaded or faint swelling of the mouth, throat or tongue, which can cause breathing and swallowing difficulties wheezing abdominal pain, nausea and vomiting collapse and unconsciousness