At what point does a drop in air pressure cause altitude sickness?

Altitude sickness can occur following a drop in air pressure at altitudes above 8,000 feet. Altitude sickness usually only occurs when a person has not been gradually exposed or acclimatized to the low air pressure in advance, according to Medical News Today.

Altitude sickness is also known as acute mountain sickness (AMS), hypobaropathy and Acosta disease. More severe forms of altitude sickness typically occur at heights above 12,000 feet. The symptoms usually include severe headaches, dizziness, nausea and exhaustion. It occurs when the amount of oxygen molecules in each breath decreases, causing an increase in breathing and heart rate, according to the Medical News Today.