The singer-songwriter, from St Andrews in Fife, said she had permanently lost the hearing in her left ear three years ago, after initially experiencing tinnitus.
She revealed she had recently started getting tinnitus in her right ear, which had led her to fear career-ending hearing loss if she does not step back from her current "intensive" schedule.
She said that with "huge regret and sadness" she would be unable to appear in a string of US dates supporting rock duo Hall & Oates that were scheduled to start next month, while her own headline shows would be rescheduled "in a less intensive way for 2022".
Tunstall, 46, broke the news last night in an emotional online post to her followers online, in which she promised to see fans "soon - in rude (and rocking) health!"
She said: "The decision to pull myself out of my Summer 2021 touring schedule has been an extremely difficult one to make. Playing live has been my life for the last 20 years, and is my deepest passion.
"Permanently losing 100% of my hearing in my left ear overnight whilst on tour in 2018 was an enormous shock, and the result of years of touring without adequate periods of rest, which caused an acute physical breakdown.
"After a recent run of consecutive shows and travel in July, I have experienced some issues with my right ear; a small amount of tinnitus - which is exactly how the breakdown of my left ear began.
"My thoughts on touring so intensively and consecutively have made me question whether my remaining hearing will be able to handle it, and as a result I have decided that the only healthy way forward for me as a 'live' musician is to completely avoid lengthy back-to-back touring which causes inevitable exhaustion and stress.
"To move forward safely in my career, I must ensure that my touring schedule leaves adequate rest between smaller batches of shows.
"With huge regret and sadness, this means I will no longer be able to join Hall & Oates on their incredible tour. It is hard to fathom pulling out of such a wonderful opportunity. Hall & Oates, The Band, Management, Crew, fans and organisers have all been so wonderful to me.
"All headline shows I have during the time period of the Hall & Oates dates will be rescheduled in a less intensive way for 2022, and tickets will be honoured for the new dates.
"I wish to play live and create music for the rest of my life, but to best ensure I will be able to do so, I must put my hearing health first as it could be the difference between being able to be a musician or not.
"I love you, thank you always for your support and understanding, and I hope to see you somewhere before too long! KT x"