The Eustachian Tube normally has a decrease function in childhood and this is due to the developmental anatomical differences and children are also susceptible to upper respiratory tract infections, allergies, large adenoids and some children are born with a cleft palate.  In adults rarer causes are, after radiotherapy, tumours of the back of the nose after trauma and various infections including TB and HIV.  There also seems to be a familial tendency with Eustachian Tube dysfunction. 

Eustachian Tube Dysfunction: