The most common cause of hearing loss is NIHL (noise-induced hearing loss). 65 decibels is what we are used to in our normal levels of conversation. At gigs and concerts, the sound level can reach as high as 120 decibels. What most people don’t realise is that when your ears are exposed to the sound at 110 decibels, only two minutes of exposure is enough to start causing hearing loss. Imagine what would happen if you spend hours at a concert, under that level of exposure. If you attend concerts on a regular basis, then the risk is even higher.
Every time you expose yourself to such high levels of sound, you risk tinnitus or NIHL, both of which are permanent. The damage to your hearing is irreversible. You can get hearing aids, but you can't get your hearing back.
You may have sometimes noticed temporary ringing in your ears after a concert, or a sporting event, or being somewhere equally loud. That may have been TTS (Temporary Threshold Shift), which was assumed to be temporary, since the ringing stops after a while. However, research has found that it is not the case. mention that "the tiny microscopic hair cells in the inner ear were affected by repeatedly being exposed to loud noises. New research done on animals and now humans is showing that it not just the hair cells that are being affected." What they discovered is that even one concert can damage hearing nerve fibres, which potentially affects your ability to understand speech.
That's why it's important to use earplugs when you are attending concerts. Of course with technological improvements, it is possible to get earplugs that let you enjoy the music without sacrificing the quality, and without costing you your hearing.