We demonstrated that indole‐3‐acetic acid (3‐IAA) derived from gut Parabacteroides distasonis (P. distasonis) binds to aryl hydrocarbon receptor (AhR) in bladder cancer cells and downregulates FASN transcription, thereby increasing sensitivity to ferroptosis and suppressing the development of bladder tumors. The gene discussed is AHR; the disease is urinary bladder carcinoma.