The sweat and breath of over 4 million tourists who gape at the exquisite frescoes at the Sistine Chapel in the Vatican City are damaging the Renaissance period works of art, a top official has warned. The Sistine Chapel has between 15,000 and 20,000 visitors a day, the Daily Telegraph reported Friday.

The Sistine Chapel is the best-known chapel in the Apostolic Palace, the official residence of the Pope in Vatican City.

Art custodians expressed alarm over the state of the exquisite paintings which adorn the chapel following the first cleaning operation for four years.

The Sistine Chapel is subjected to a huge influx of visitors every day, with each tourist responsible for adding to the invisible cloud of dirt, dandruff and other microscopic debris that floats up into the uppermost reaches of the famed church.

The delicate cleaning operation, which began in mid-July, was carried out by a team of 30 experts working at night — the only time that the Sistine Chapel is free of tourist hordes.

The restorers accessed the chapel’s high walls and ceiling in crane-mounted cherry pickers and used goat hair brushes to remove “unimaginable amounts” of dust from the frescoes by Michelangelo and other Renaissance masters, head of the Vatican Museums Antonio Paolucci said.

“Every one of the 4.5 million tourists who visits the Sistine Chapel each year brings in dust on their clothes and shoes,” he said. “They shed tiny particles of skin and of course they breathe. We can’t do anything about that, but each human body increases the humidity inside the chapel. All this produces an accumulation of dust on the frescoes which cover the chapel’s walls,” Paolucci said.

“They are not going to start crumbling tomorrow, but over a long period of time there is a danger that they will be damaged. With advanced technical instruments it is possible to maintain constant levels of humidity and temperature but the systems we have at the moment are between 15 and 20 years old and need replacing.”

“If we want to preserve the Sistine Chapel for future generations, this is the challenge that we need to face.”

Vatican officials will work with technicians to ascertain how to replace the climate control system, with the cost as yet unknown.

Built by Pope Sixtus IV between 1473 and 1484, the Sistine Chapel has been used for centuries as a private place of prayer for popes and for conclaves, the secretive meetings held by the College of Cardinals after the death of a pontiff to choose a successor.

It is also featured in the film “Angels and Demons”, with the film’s producers having to surreptitiously take photographs of the chapel and then recreate it digitally after the Vatican banned them from filming out of displeasure over the far-fetched plot of Dan Brown’s novel.