If you ascend without proper acclimatization, at around 9,000 feet, your lungs may begin to swell because the blood vessels constrict. Symptoms include a persistent cough and labored breathing.

If the swelling in your lungs worsens, high-altitude pulmonary edema (HAPE) can occur. Symptoms are a bluish discoloration of the skin, rapid breathing, and fever. The most effective treatment is to descend immediately.

In order to supply your body with enough oxygen to maintain functioning, your heart must work harder. You will have an increased heart rate and greater force per beat. Your body creates more oxygen-carrying red blood cells, which is generally helpful.

However, it also thickens your blood and could precipitate heart attacks in those susceptible to it.

At high altitudes, the low oxygen can cause spasms in the arteries that supply blood for your sight, causing transient blindness in some climbers.

Increased ultraviolet radiation can lead to inflammation of the cornea, causing snow blindness.

Due to a lack of oxygen in the intestines, digestion slows down. As a result, 81 percent of mountaineers experience nausea or vomiting. 

Most of those climbing Everest become anorexic, especially as they approach the peak.

During exposure to frigid temperatures like those on Everest, you can suffer from frostbite.

The best way to prevent frostbite is to ensure you have the highest-quality mittens, socks, boots, and headgear.