Tinnitus is most often described as a ringing in one or both ears, but sounds can also be perceived as static, humming, whistling, buzzing, grinding or hissing. As no one else can hear the sounds (except in very rare cases), tinnitus is a very unique and personal condition to each person experiencing it. It is a symptom, most commonly of hearing loss, rather than a disease—and it is rarely a sign of a serious underlying condition. Some people hear noises that are constant and steady, while for others they may pulsate or be more intermittent. Many of those who experience tinnitus find that it is relatively mild and gradually improves over time. However, severe cases of this condition can sometimes disrupt sleep, concentration, and the enjoyment of everyday activities.