Hypoxia-inducible factors (HIFs) are proteins that help cells respond to low oxygen levels, a condition known as hypoxia. When oxygen is scarce, HIFs activate specific genes that promote processes like red blood cell production and blood vessel formation, which help improve oxygen delivery to tissues. HIFs are crucial for maintaining cellular function in various conditions, including during exercise or in certain diseases. They play a significant role in cancer biology, as tumors often experience hypoxia and can exploit HIFs to grow and spread. Understanding HIFs is important for developing therapies for related health issues.