Heavy tourist traffic through the Sistine Chapel is endangering the world-reknowned frescoes decorating its walls, the head of the Vatican museums said.

“Humans breathe and perspire and the dust and humidity endanger the frescoes,” said the director of the Vatican Museums, Antonio Paolucci.

Mr Paolucci said that each year 4.5 million people – between 15,000 and 20,000 every day – visit the chapel.

“Too much human presence is putting on pressure and we need to check it carefully and effectively,” remarked Mr Paolucci.

Signs of danger for the frescoes, which include Michelangelo’s The Last Judgement behind the altar and the nine scenes from the Book of Genesis he painted on the ceiling of the chapel, were detected this summer during a routine dusting.

But Mr Paolucci said the obvious solution, limiting the number of visitors, “would not be right” towards people who come from all over the world to admire the frescoes in the chapel, where the cardinals’ conclave gathers to elect the Pope.

On the contrary, the Vatican Museums have decided to open their doors to visitors also on Friday nights in September and October.

The Friday night openings “involve a limited number of people and allow to spread out the pressure,” Mr Paolucci explained.

He also ruled out a deep restoration of the chapel like the one that took place in the 1980s and 1990s.

Mr Paolucci called for “deploying for the conservation no less creativity and intelligence than that used by artists that created it”.