Middle Ear Disease
The middle ear is a pea sized, air-filled cavity separated from the outer ear by the paper-thin eardrum. Three tiny ear bones are attached to the eardrum. When sound waves strike the eardrum, it vibrates and sets the bones in motion that transmit to the inner ear.
A healthy middle ear keeps air at the same pressure as outside the ear, allowing free vibration. Air enters the middle ear through the Eustachian tube which connects the back of the nose to the ear. The pop you hear when you yawn means your Eustachian tube has sent a tiny air bubble to your middle ear to equalize the air pressure.
Fluid in Ears
Blockage of the Eustachian tube during a cold, allergy, or upper respiratory infection and the presence of bacteria or viruses lead to fluid (a build-up of pus and mucus) behind the ear. This is the infection called acute otitis media, the most frequent diagnosis recorded for children who visit physicians for illness. It is also the most common cause of hearing loss in children.
This infection can cause earache, swelling, and redness, as well as hearing problems.