Sound levels are measured in decibels and based on a scale of 0 (low) to 140 (high). Sixty decibels (dB), which is about the level of normal conversation, is considered a safe level of sound. The National Communication Disorder Institute reports that 85 decibels and above can cause damage to the inner ear and may result in hearing loss. Concerts fall around 105-110 dB, as do lawnmowers and bulldozers, but it is believed that the risk of hearing loss is low since the length of time your ears are exposed to these levels is relatively short. The risk is greater among people who are regularly exposed to these high levels and do not wear protective ear coverings.
If you are concerned about your son's hearing, the best thing to do is have him get a hearing test to check for any hearing damage. It is not easy for a person to detect mild hearing loss because there are usually no obvious signs; only when hearing loss becomes more severe is it noticeable. Signs of severe hearing loss may include distorted or muffled sounds that are particularly obvious in social situations. Unfortunately, these signs seem to be present only after permanent hearing loss has occurred.
Attending concerts a few times each year is unlikely to cause permanent hearing loss, but everyone should avoid repeated, frequent exposure to loud sounds.