Why does altitude sickness cause headache?

At altitude, each breath contains the same proportion of oxygen as at sea level, but the lower air pressure makes it harder for oxygen to move into the blood. Your body responds by changing breathing, circulation, and fluid balance. These adjustments can contribute to a pressure-like or throbbing headache, often with tiredness, poor sleep, dizziness, or reduced appetite. Headache is a very common presentation of Altitude Sickness. A headache also has many other possible causes, including dehydration, alcohol, missed meals, eye strain, or a viral illness.

Stop ascending while symptoms are present and rest at the current elevation. Drink fluids regularly, eat if you can, and avoid alcohol and strenuous activity. A simple pain reliever may help if it is normally safe for you, but it does not make continued ascent safe. If symptoms do not settle, descend to a lower elevation. Planning a gradual ascent gives the body more time to adjust. See our information on Headache for other common contributors.

Descend and get urgent medical help if the headache becomes severe, worsens despite rest and descent, or comes with confusion, unusual drowsiness, trouble walking steadily, fainting, breathlessness at rest, chest tightness, or a persistent cough. These features can signal a serious altitude-related illness. Seek medical advice promptly if vomiting prevents you from drinking or taking medicines.

Ask whether your itinerary allows enough time to acclimatise, whether any health condition or medicine changes your altitude plans, and what symptoms should make you descend immediately. If you have had altitude illness before, ask about an individual prevention plan before travel.