It was first reported in 2010 that the pillars of Kolkata's landmark Howrah bridge were being used as spittoons by pedestrians who chewed gutkha – a tobacco product popular with millions in India.

Engineers who surveyed the cantilever structure then reported that the struts supporting the girders of the bridge had already lost half of their metal casing: The corrosion was apparently caused by acids in the gutkha.

Soon the Lions Club of Howrah launched a "Save Howrah Bridge from Spit" campaign urging people not to spit on the bridge.

The campaign spread across the city of Kolkata, where reddish-brown gutkha stains are visible almost everywhere — pavements, streets, office staircases, business houses, and residential complexes. Prominent citizens of Kolkata joined the campaign in an effort to rid the city of the ugly stains.

Gutkha is a commercially produced pre-packaged mixture of crushed betel nut, tobacco, lime, paraffin, and other "secret" ingredients, many of which are carcinogenic and addictive.

Some brands of gutkha also contain lead, arsenic, chromium, nickel, and cadmium, which are as bad as nicotine. To make its shelf life longer, magnesium carbonate – which is used in fire extinguishers and is a known carcinogen – is also added to gutkha.

Activists reported about a year ago that one-third of men and one-fifth of women across India are addicted to chewing tobacco and gutkha was its most popular form.

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Because of its candy-like flavor and dirt-cheap prices — 4 to 6 cents per sachet — gutkha has become increasingly popular among children, who chew and even eat it. An estimated 5 million of India's children are addicted to gutkha, and every day another 5,000 try it for the first time, according to reports last year by the American Cancer Society.