Carnauba wax is a product you may not have heard of, but you have almost certainly consumed it - it is added to sweets to stop them melting, to pills to make them easier to swallow and as a thickener in lipstick and mascara. Workers in Brazil's poor north-eastern state of Piauí rely on harvesting wax from carnauba palm trees to earn a living. But the power is in the hands of big business who, authorities say, are turning a blind eye to exploitation.