The programme advises people "don't blush…look before you flush" to raise public awareness of rectal bleeding – often an early sign of colon cancer.
Yet Mourad Habib, a clinical research fellow at St James's University Hospital, says that the lavatory disinfectants now sold in supermarkets are mostly blue in colour and change the water blue, which makes looking for blood quite difficult.
He suggests that we stop selling colouring agents and replace them with colourless ones or even use reagents that turn a certain colour in the presence of minor blood amounts.
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