Four mountain climbers have died while climbing Mount Everest, according to news reports.
Two of those climbers -- a 61-year-old German and a 44-year-old South Korean -- reportedly died of altitude sickness and exhaustion, the International Business Times reported.
A Chinese climber and a Canadian born in Nepal were also found dead, and a sherpa from Nepal is still missing, according to the International Business Times .
The deaths occurred while the climbers were descending from the mountain, Mother Nature Network reported.
"Climbers spend their energy on the ascent and they are exhausted and fatigued on the descent," Ang Tshering Sherpa, of Asian Trekking adventure agency, told Mother Nature Network.
Altitude sickness, also known as acute mountain sickness, is usually experienced by people when they are above 8,000 feet, or 2,400 meters, according to the A.D.A.M. Encyclopedia. It occurs as a result of low air pressure and oxygen, and the likelihood of altitude sickness rises the faster a person climbs.
Symptoms include headaches, loss of appetite, vomiting, feeling weak, problems sleeping, and feeling dizzy, according to WebMD.
When the condition is more severe, a person may experience confusion, skin discoloration, coughing up blood, paleness, loss of consciousness and shortness of breath, A.D.A.M. reported. Severe cases of altitude sickness can lead to death because of brain swelling or fluid in the lungs.
WebMD reported that the best option for treating altitude sickness is to go to a lower elevation, although oxygen or a pressure chamber can also help to treat the condition. A drug called acetazolamide, or Diamox, could also help with breathing, while a drug called dexamethasone, or Decadron, can help to reduce brain swelling, according to the National Institutes of Health.
To prevent altitude sickness, the NIH recommends that people climb gradually, stopping to rest for at least a day or two every 2,000 feet that is climbed above 8,000 feet.