Why is an untreated acute allergic reaction a life-threatening situation?

Untreated acute allergic reaction is a life-threatening situation because its symptoms can progress quickly. The most dangerous is the Anaphylaxis. It can be triggered by drugs, food, or injections, which a person may experience itching, swelling, difficulty in breathing, panic, and collapse. The worse is cardiac arrest when not treated immediately. Moreover, a prolonged illness may also develop as its late phase such as severe asthma.