Why do people have a runny nose after catching a cold?

When a person catches a cold, his nose will run clear and runny. What is going on?

Before talking about this issue, we must first talk about the structure of the human nose. The nose is the beginning of the respiratory tract and is also the olfactory organ. It is divided into three parts: the nose, the nasal cavity and the paranasal sinuses. The cavity in the nose is called the nasal cavity. There is a complete layer of mucous membrane on the inner surface of the nasal cavity. There are many mucus glands and a rich capillary network in the mucous membrane, which constantly secrete some mucus and water. According to physiologists, the amount of mucus and water secreted within 24 hours is 500 to 1000 ml. The amount is related to the dryness and humidity of the air. Under normal circumstances, the liquid secreted by the nasal mucosa is roughly equivalent to the evaporation rate of water when the air enters and exits the nasal cavity. In other words, the nasal mucosa secretes as much liquid as the air takes away water when it enters and exits the nasal cavity. Therefore, a healthy person usually does not have a runny nose.

The fluid secreted by the nasal mucosa has multiple functions. First, it can moisten the air entering the lungs to prevent the air from being too dry and damaging the lungs; secondly, it contains very viscous liquid, which is evenly distributed on the surface of the nasal mucosa, so that dust and microorganisms entering the nasal cavity are stuck, preventing dust and Microorganisms invade the lungs; in addition, the mucus also contains lysozyme, which can dissolve and kill stuck bacteria.

Why does the nasal mucosa sometimes secrete so much fluid that it flows out? There are several situations: First, when the nasal mucosa cannot defeat certain microorganisms or foreign bodies, leading to the early stages of infection in the respiratory system, such as colds, measles, scarlet fever or acute rhinitis, clear water will flow from the nose to wash away part of the infection. microorganism. Second, when the weather is cold and there is less clothing, the rich capillary network of the nasal mucosa cannot warm the inhaled air to a sufficient level, and can only help by secreting a large amount of fluid. These fluids are warm when they are first secreted, and become cooler after being absorbed by the cold air inhaled, so the nasal discharge is cold. Third, when the body's resistance is reduced, the nasal cavity is allergic to the cold air flow and reacts instinctively, exuding a large amount of clear water and mucus.

It can be seen that runny nose is a defensive physiological reaction of the human body. As long as you actively exercise and enhance your body's ability to adapt to cold, you can reduce or cure the phenomenon of runny nose.