Phycocyanobilin was observed to inhibit NADPH oxidase activity and reduce oxidative stress;68 down‐regulation of NADPH oxidase has a high potential in therapeutic and preventive medicine.69 Furthermore, extracts of spirulina have anti‐cancer activities attributed to phycocyanin, a protein with the phycocyanobilin chromophor as prosthetic group.70 This evidence concerns the gene FMO5 and cancer.