Anaphylaxis is a severe allergic reaction that develops as a result of the immune system's excessive and violent response to allergens. This reaction occurs when triggers such as foods, chemicals, medications, or insect stings enter the body. The immune system rapidly releases chemicals into the body, triggering a widespread reaction that can lead to shock and various symptoms that may impair vital organ functions.

Common causes of anaphylaxis include:
* Foods (peanuts, tree nuts, milk, eggs, fish, shellfish, wheat, soy, sesame are the most common childhood triggers)
* Medications
* Insect stings (especially bee venom, a common cause in both children and adults)
* Chemicals
* Rarely, pollen, red meat, and vaccines

Beyond all these known causes, anaphylaxis that occurs without a clear trigger is called 'idiopathic anaphylaxis.' This type is more common in adults, especially the elderly, than in children.