Hypoxia is when the tissues of your body don’t have enough oxygen. When you breathe, you take oxygen into your lungs, where it travels through your airways out into small sacks called alveoli. From there, it gets picked up by your blood in small vessels that travel close to the alveoli (capillaries). Finally, it travels through your blood out to other tissues. You can think of oxygen as billions of passengers flying into the airport (your lungs). They get picked up at the gate and get on the highway (blood vessels) to be taken to their destination (your tissues). As the oxygen gets dropped off, it makes room for a different passenger to be picked up: carbon dioxide. Carbon dioxide is a waste product, which is then taken back to your lungs and exits your body when you breathe out. If not enough oxygen gets through at any place on the journey, it can lead to hypoxia. Airflow and blood flow are both important to the process. This is why lung disease and heart disease both increase your risk of hypoxia. Someone who experiences hypoxia is called hypoxic.