Like all great beauties weathered by the rigours of modern life, the Taj Mahal could do with a facial.

Considered by many to be the most beautiful building in the world, the monument to love has stood the test of time since the Mogul emperor Shah Jahan completed it in 1654 in memory of his second wife, Mumtaz Mahal. The white marble tomb – one of the seven wonders of the modern world – looks, however, decidedly peaky despite a decade-long effort to restore its complexion.

The Indian Parliament was told in a report this week that air pollution from local industry was again discolouring the Taj’s gleaming surface day by day. Blame for its yellow tinge has been laid on consistently high levels of “suspended particulate matter” – otherwise known as grains of dirt – created by the burning of fossil fuels at nearby factories and by clouds of dust from roads.

The proposed solution for India’s biggest tourist attraction, located in the city of Agra, 130 miles (210km) southeast of Delhi, is appropriate for an object of beauty: a therapeutic mud pack.

“To restore the pristine glory of the Taj Mahal . . . the clay-pack treatment, which is non-corrosive and non-abrasive, [should be] carried out for the removal of the accretionary deposits,” the report said.

The process, which takes two to three months, is labour-intensive and expensive. Workers on scaffolding smear wet mud on the surface of the building and let it dry before washing it off.

The lime-rich multani mitti – a type of clay found in northern India and used in modern face masks and Ayurvedic body treatments – draws out most of the accumulated dirt.

“This technique is an old Indian method and does not use any chemicals,” P. Dayalan, the superintendent at Agra for the Archaeological Survey of India, told The Times.

“It is a slow process. We hope the monsoon will clean off some of the dust particles which move around more in the summer because of the heat and wind. But some parts will need special attention.”

The treatment, which costs about $230,000 (£115,000) a time, was last carried out three years ago and will need to be repeated regularly to maintain the memorial’s whiteness, according to the Archaeological Survey. It plans another session later this year.

Although Lord Curzon, the British Viceroy of India, ordered the restoration of the Taj in the early 20th century after it had fallen into disrepair, conservation efforts only really began ten years ago.

The Supreme Court ordered the closure or relocation of thousands of smoke-spewing iron foundries, brick kilns and glass-making units near the massive memorial, which is visited by three million tourists a year. A ban on motor vehicles around the World Heritage site was also imposed, forcing visitors to take rickshaws, electric buses or horse-drawn carriages for the last mile and a half.

Experts monitoring the impact of air pollutants have found sulphur dioxide and nitrous oxide within permissible limits but dust levels are very high. Environmentalists blame illegal mining in the surrounding hills, the dryness of the adjacent Yamuna river-bed in the hottest months and a rising number of diesel trucks on badly maintained roads.

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