In Dharavi, the largest slum in Asia, Alam clutches his face in pain. The plastic-crushing machine he operates has jammed again, sending a metal part flying into his forehead. A small crowd gathers as blood wells up around his hairline but within minutes he is back at work, cramming bottles into the machine’s churning jaws.

Time out for a check-up is not an option. With more than 1m people inhabiting this patch of land between Mumbai’s western and central railway lines, barely 1.75 sq km in area, there is plenty of competition for an unskilled job paying Rs4,000 ($86, £45, €68) a month.