The listener perceives a gradual drop in loudness even though the volume control setting hasn't changed. The acoustic isolation of headphones tends to highlight this dulling effect. It is all too easy for headphone listeners to turn up the volume to the point where hearing is at risk. Interestingly, most people find it difficult to distinguish between 85dB and 100dB SPLs, despite that the latter is more injurious to hearing. Therefore, it is important to avoid listening fatigue by resting the ears in silence after long sessions with headphones and to fight the temptation to turn up the volume.
Personal stereos are another source of hearing damage risk.
Aerobic exercise diverts blood from the ears to the limbs, and leaves the inner ear more vulnerable to damage from loud sound. A Swedish study estimated that the risk of hearing loss is doubled when listening to headphones at high volume during aerobic exercise. The study recommends limiting headphone use during exercise to one-half hour per day at half volume. Even if one's hearing has been subjected to major acoustic shock, quick medical intervention may minimize the trauma. On the other hand, hearing damage can also be gradual, cumulative and without obvious warning signs.