Asked by: Iqra Shahzad, London
Your saliva is mostly recycled, rather than produced, because you are constantly swallowing and reabsorbing it. But the flow rate is around 30ml of saliva an hour – a bit more when you’re eating, a bit less when you’re sleeping. That’s a wine bottle full every day, or 20,000 litres in your lifetime. In other words, 53 bathtubs full to the brim with saliva!