Commonest cause of Eustachian tube disease is

Adenoids cause eustachian tube dysfunction by a) Mechanical obstruction to tubal opening b) Acting as a reservoir for pathogenic organisms c) In case of allergy, mast cells of the adenoid tissue release inflammatory mediators which cause tubal blockage (Ref: Textbook of diseases if ENT, PL Dhingra, 7th edition, pg no. 64)