Which organ is primarily affected by a severe allergic reaction (anaphylaxis)?

In a severe allergic reaction, or anaphylaxis, the respiratory system is primarily affected due to the rapid onset of airway constriction and swelling. This reaction leads to difficulty in breathing, wheezing, and in severe cases, can cause the airway to be critically compromised. The body releases a large amount of histamine and other chemicals in response to allergens, which causes blood vessels to dilate and the muscles around the airways to constrict, making it challenging for air to move in and out of the lungs.

While the heart and the liver are important organs that can also be impacted during anaphylaxis—due to effects on circulation and metabolism—the primary and most immediate concern during an anaphylactic reaction is the respiratory system. This is why measures to ensure airway patency and provide oxygenation are critical in the emergency management of anaphylaxis.