Many times there is no easy answer to the question of what caused a particular person to become deaf or hard of hearing.  Hearing loss can occur because of heredity, illness, accident or aging.  About half the time, genetic factors are the most likely cause of deafness.  However, most deaf parents have hearing babies; deafness is not commonly passed on from parent to child.  In 90 percent of the cases a child with hearing loss is born to a family with no previous contact with or knowledge of deafness.

In the remaining cases of hearing loss where a cause is identified, environmental factors are responsible.  These include accidents, constant high noise levels and illness.  A child can lose its hearing before birth if the mother has rubella or another viral infection.  During the actual birth process, factors like a loss in the oxygen supply can affect hearing.  Premature babies can have hearing loss in addition to other conditions.  Illness or infection in young children can affect hearing as well.

Exposure to explosive sounds, tumors, injury to the skull or ear, tumors or a combination of these factors can cause hearing loss.  Some medications may specifically harm the ear.  A congenital brain abnormality, tumor or lesion of the central nervous system can also cause hearing loss.   High noise levels that are constant can cause progressive and eventually severe hearing loss, and this is a growing concern, especially for young people.

The National Center for Health Statistics of the U.S. Department of Health and Services estimates that three out of four people with hearing loss began to have trouble hearing after age 18. Only 5 percent reported onset before they could speak, or before three years of age.

About a third of the 19 million deaf and hard of hearing adults in the U.S. report that their loss is due to some sort of noise. Twenty-eight percent say their hearing loss is due to age, and 17.1 percent report that it is due to infection or injury. A small number -- 4.4 percent -- report the hearing loss as beginning at birth.

The Center for Assessment and Demographic Studies, in their annual survey of hearing impaired children and youth, estimate that heredity is the leading known cause of hearing impairment at birth. It accounts for 13 percent of hearing impairments reported at birth. One out of every 2,000 children born will inherit hearing problems. Genetic deafness is less likely to be accompanied by other health problems.

Pregnancy/birth complications account for 8.7 percent of hearing impairments reported at birth. This includes Rh incompatibility, prematurity, and birth trauma. When it results in a lack of oxygen and cerebral hemorrhage, premature birth can cause damage to the nervous system and subsequent hearing loss. When there is a blood type incompatibility between mother and child, some children will be born with a hearing loss and others will be born with cerebral palsy.

The most common cause of hearing loss in children is otitis media, or ear infection. According to the National Institute on Deafness and other Communication Disorders, otitis media is the major reason why young children are taken to the emergency room or the physician's office and the most frequent reason doctors prescribe antibiotic therapy for children.

Another cause of hearing impairment after birth is bacterial meningitis. Boys are more likely than girls to contract this disease. Children under four are most susceptible to the disease, which is an inflammation of the lining of the brain. Most children are vaccinated against one type of meningitis, Hib, but there are other strains which are equally dangerous.

In the past, several factors caused deafness in children and adults. Between 1963-1965,a rubella epidemic swept through the country. Pregnant women who contracted rubella often had babies with hearing impairments, visual problems and heart defects. Now, pregnant women are much less likely to contract rubella, so the incidence of deafness due to this complication of pregnancy is greatly reduced.