Final answer:
Michael's life-threatening reaction would be caused by a food allergy to peanuts. When Michael accidentally eats a peanut, his immune system responds by attacking the peanut protein as if it were a harmful invader.
Step-by-step explanation:
Michael's life-threatening reaction would be caused by a food allergy to peanuts. When Michael accidentally eats a peanut, his immune system responds by attacking the peanut protein as if it were a harmful invader. This triggers a series of immune responses that can lead to severe symptoms, such as swelling of the lips and mouth, difficulty breathing, and in some cases, anaphylaxis.