Previous reports have paradoxically shown that certain bacterial tryptophan metabolites can protect cancer cells from ferroptosis.[46, 47] For instance, trans‐3‐indoleacrylic acid (IDA), a tryptophan‐derived metabolite produced by P. anaerobius, has been shown to activate AhR and upregulate ALDH1A3, resulting in increased NADH production and inhibition of ferroptosis in tumor cells.[11] In contrast, our study demonstrates that a different microbial indole metabolite, 3‐IAA, activates AhR signaling to induce ferroptosis and inhibit tumor growth. The gene discussed is ALDH1A3; the disease is cancer.