Doctors at Mumbai's Sion hospital say dozens of patients arrived at the casualty ward complaining of giddiness, vomiting and headaches. The vast majority were children from one of Mumbai's largest slums, Dharavi. Most are in a stable condition. It's believed they developed a reaction to coloured powders they were throwing. Across the country, millions of people from all walks of life smear and cover themselves from head to toe in bright paints and powders as is custom for Holi. But there has been concern for some time that some of the artificially-produced dyes, which are cheap to buy, contain harmful toxic chemicals which can lead to serious skin and breathing problems. There has been a push in recent years to encourage more revellers to use organic and environmentally-friendly dyes to avoid health risks.