FICZ is a potent endogenous ligand for the aryl hydrocarbon receptor (AhR), making it a key molecule in studying immune regulation and cellular responses. It is widely used in research to activate AhR signaling pathways, which play a role in modulating immune function, particularly in promoting regulatory T cell development and suppressing excessive inflammatory responses. Due to its role in AhR activation, FICZ is applied in studies related to autoimmune diseases, such as multiple sclerosis and inflammatory bowel disease, to understand how AhR influences disease progression. It is also used in dermatology research, especially in models of skin inflammation and UV-induced immune suppression, as FICZ is generated in the skin upon UV exposure. Additionally, FICZ serves as a tool compound in cancer research to explore the dual role of AhR in tumor promotion and suppression, depending on context and cell type. Its high potency and natural origin make it valuable for probing physiological AhR functions in vitro and in vivo.