Question

why nose bleeding starts at high altitude

Answer 1

Hot climates with low humidity or changes from bitter cold to warm, dry climates can cause drying and cracking inside the nose, which can lead to a nosebleed. High altitude - asaltitude increases, the availability of oxygen decreases, making the air thinner and drier. The dryness can cause the nose to bleed.

Answer 2

the blood pressure in the body balances the atmospheric pressure near us

as we move to higher altitudes the atmospheric pressure decreases

since the blood pressure is higher in our body compared to the surroundings

the blood vessels near our nose rupture hence our nose bleeds in high altitudes