The pressure in the ears is a normal phenomenon because the ears are divided into the outer ear, middle ear and inner ear, of which the middle ear has the eustachian tube, which communicates between the middle ear cavity and the nasopharynx. Under normal circumstances, the pharyngeal opening of the eustachian tube is closed, and when the eustachian tube is open, the air pressure in the middle ear is balanced with the atmospheric pressure. However, when riding a train through a cave or tunnel, the air pressure around the car is higher than the air pressure outside the tunnel, and the outside air pressure changes within a short period of time, while the air pressure inside the middle ear has not yet had time to change, and the air pressure inside and outside the eardrum becomes unbalanced, which can lead to a feeling of pressure and, in severe cases, pain. The pressure can be relieved by swallowing saliva, opening and closing the mouth, etc. The pressure will disappear quickly and the ear will not be damaged at this time.