Scientists believe they have found a gene that may be responsible for glue ear in children.
Half of babies under a year old will experience glue ear
The condition, also called otitis media, meaning inflammation of the middle ear, is the most common cause of hearing impairment in children.
Half of UK children under the age of one get glue ear, and a third of one to three year olds have repeated bouts.
The work in mice, published in Public Library of Science Genetics, pinpoints a gene called Evi1.
In otitis media, the inflammation often begins when infections that cause sore throats, colds, or other breathing problems spread to the middle ear - the part of the ear that lies behind the eardrum .
There are many reasons why children are more likely to suffer from otitis media than adults.
Children have more trouble fighting infections, partly because their immune systems are still developing.
Also the passageways connecting the ears to the throat are small and can get blocked meaning any fluid cannot drain and will collect in the ear.
As the fluid increases, the child may have trouble hearing because the eardrum and middle ear bones are unable to move as freely as they should.
As the infection worsens, the fluid gets thicker and glue-like and many children also experience severe ear pain.
Eventually, too much fluid can put pressure on the eardrum and tear it.
Antibiotics may be given if there is infection. But in persistent cases an operation is often needed to drain the ear and insert tiny drainage tubes called grommets.
Scientists have known for some time that genes play a role in otitis media, but until now they have been unable to pinpoint the exact pathways involved.
Professor Steven Brown, and colleagues at the Medical Research Council Mammalian Genetics Unit, studied a mouse with hearing loss, which they called Junbo.
Like some children with otitis media, the Junbo mouse had severe, recurrent glue ear.
The Evi1 gene carries the genetic code for a protein that helps to translate other DNA code into instructions for the body. In the Junbo mouse, this appeared to affect the cells that line the middle ear when there is inflammation.
Professor Brown said: "Because the Junbo mouse provides a model of how otitis media affects children I hope that it will help researchers to figure out new ways to tackle this disease.
"Five million school days are missed every year due to otitis media."
Dr Mark Downs of The Royal National Institute for Deaf and Hard of Hearing People said: "This is a very exciting development.
"Further studies would need to be carried out to ascertain whether the gene is a common cause of glue ear in children, but it does yet again highlight the important role genetic factors play in many forms of hearing loss."