Snot, also known as nasal mucus, plays a powerful role in protecting us from disease – and its colour alone can provide insights into what's going on in our bodies, BBC reports. In Ancient Greece, snot was thought to be one of the four bodily fluids responsible for balancing human health and personality. The physician Hippocrates developed a theory stating that phlegm, blood, yellow bile and black bile were the four humours. A person's balance of these humours could dictate their temperament; an excess of any of them could cause illness. For instance, phlegm was thought to be made in the brain and lungs, and during the cold and wet seasons, it could become too abundant and even cause epilepsy. Somebody with a phlegmatic personality would have a cold, damp and aloof character. Of course, we now know that snot doesn't affect people's personalities or cause diseases – rather, it helps to protect us from them. And though nobody likes a runny nose or flinging snot across the room in a sneeze, the mucus in our nasal passages is arguably one of the wonders of the human body. It protects us from intruders, and it has a unique composition that can reveal profound insights into what is going on inside us. Now scientists are hoping to hone the powers of snot to better diagnose and treat everything from Covid-19 to chronic lung conditions. The gooey substance shields the insides of our nose, moisturising the nasal passages, and trapping any bacteria, viruses, pollens, dirt, dust and pollution trying to get into our body through our airways. Aided by hundreds of tiny hairs, snot is a barrier between the outside world and our inner one.
