Around 1801, Beethoven began to lose his hearing. He suffered a severe form of tinnitus, a "roar" in his ears that made it hard for him to appreciate music and he would avoid conversation. The cause of Beethoven's deafness is unknown, but it has variously been attributed to syphilis, lead poisoning, typhus, or possibly even his habit of immersing his head in cold water to stay awake. Over time, his hearing loss became acute: there is a well-attested story that, at the premiere of his Ninth Symphony, he had to be turned round to see the tumultuous applause of the audience, hearing nothing. In 1802, he became depressed, and considered committing suicide. He left Vienna for a time for small Austrian town of Heiligenstadt, where he wrote the "Heiligenstadt Testament", in which he resolved to continue living through his art. He continued composing even as his hearing deteriorated. After a failed attempt in 1811 to perform his own "Emperor" Concerto, he never performed in public again.
As a result of Beethoven's hearing loss, a unique historical record has been preserved: he kept conversation books discussing music and other issues, and giving an insight into his thought. Even today, the conversation books form the basis for investigation into how he felt his music should be performed, and his relationship to art - which he took very seriously.
There are a variety of theories as to why Beethoven suffered from hearing loss, from illness to lead poisoning. The oldest explanation, from the autopsy of the time, is that he had a distended inner ear which developed lesions over time. This theory is outlined in Beethoven et les malentendus by Maurice Porot et Jacques Miermont.
Russell Martin argued, from analysis done by Walsh and McCrone on a sample of Beethoven's hair, that there were alarmingly high levels of lead in Beethoven's system. And that high concentrations of lead can lead to bizarre & erratic behaviour, including rages. Another symptom of lead poisoning is deafness. In Beethoven's era, lead was used widely without true understanding of the damage it could lead to: in sweetening wine, finishes on porcelain, and even medicine. The investigation of this link was detailed in the book, "Beethoven's Hair : An Extraordinary Historical Odyssey and a Scientific Mystery Solved". While the likelihood of lead poisoning is very high, the deafness associated with it seldom takes the form that Beethoven exhibited. It is more likely that his generally bad health as he grew older was related to plumbism rather than his hearing loss.