What causes swollen lips and cheeks?

Answer 1

coldness

A little more...The blood in your body is used for, among other purposes, the transport of oxygen throughout the body. The part of the blood that does this is the molecule, Hemoglobin.

When hemoglobin bonds (for instance, to oxygen atoms), it reflects bright red. When it's unbonded, it's a darker blue-purple color, and that's what you're seeing when your lips and cheeks (and other parts too) turn blue. That's the symptom name -- now we ask, what caused that symptom?

When you're cold, your body tries to conserve heat by cutting down circulation to peripheral areas; places that get a lot of blood ideally, but aren't critical to life support. Your lips and cheeks are two such areas. So, when you're cold, circulation to those areas slows, and the hemoglobin gives up all its oxygen, and turns that bluish color you're seeing.

Other more serious things cause cyanosis too, and all of them related to inability to get oxygen. So, for instance, if you see someone having a coughing attack and they start turning blue, you know you're seeing something a lot more serious.

Answer 2

anaphylaxis

Usually an allergic reaction