As the Sistine Chapel celebrates its 500th anniversary, the Vatican has said it may have to limit the huge numbers of visitors because pollution is damaging Michelangelo's frescoes.

The scenes, including the moment in which God gives life to Adam with the touch of his finger, are being damaged by the breath, sweat and heat of the 10,000 to 30,000 tourists who walk through the chapel every day.

The Vatican had an air-conditioning system fitted during restorations in the chapel in the 1990s, but critics have warned that it is no longer sufficient to deal with the amount of dust and dirt being dragged in by today's visitors.

Museums director Antonio Paolucci said a specialist company has been asked to design a new air-purifying system -- but that if a solution is not found by next year the Vatican will be forced to begin reducing the number of tourists.

Michelangelo spent much of four years on his back painting the chapel's ceiling frescoes, which Paolucci said most tourists could not bear to miss on a tour of Rome, describing them as a "fatal attraction, an object of desire".