The ear's Eustachian tube is narrow and short. It is a passage which connects the space of your middle ear to that of the nasal cavity. It's role is to equalise the pressure between the two regions. This is so that if the air pressure changes then the pressure on both sides of the eardrum remains the same. This allows maximal vibration of the drum helping to improve perception of sound.
Sometimes the Eustachian tube becomes blocked by mucus, inflammation or infection. Allergies and colds can cause swelling in the wall resulting in blockage of the tube. Lack of ventilation results in fluid building up in the space of the middle ear. If chronic this is called glue ear. Children and very young people are at increased risk of Eustachian tube dysfunction. This is due to the narrowness of their Eustachian tubes.
Glue ear can result in recurrent infections and require multiple courses of antibiotics. If this occurs an ear nose and throat surgeon may consider inserting a grommet. This is to ventilate the middle ear space and prevent the buildup of fluid and infection. The surgeon makes a tiny incision in the eardrum with a scalpel. A grommet is a tiny tube with flanges on both ends. It is placed in the incision to hold it open and prevent it healing closed. Grommets usually fall out on their own after a few weeks or months and the hole in the drum heals spontaneously.