Some reasons for having excess amounts of mucus, or snot, in the nose are colds and allergies. Although the lining of the nose and sinuses produce mucus continually, the flow, consistency and color tend to change, especially with a cold, states WebMD. This is due to mucus's functions in the body, such as helping it to ward off infections and allergens.
The main function of mucus in the nose and sinuses is to act as a barrier and trap allergens, bacteria and substances like dust before they travel deeper into the body, states Healthline. Mucus production is also important when there is an illness connected with an infection, such as a bad cold or flu. In either of these cases, there is an excess of mucus production in the nose and sinuses to help the body fight the infection.
In actuality, the body produces about 1.5 liters daily of thin mucus, according to WebMD. It is only when there are allergies or a cold that people notice an excess of mucus flow, which can have a much thicker consistency. The color often changes from clear to either yellow or green. Greenish mucus is caused by white blood cells that contain a green enzyme. These white blood cells are released by the immune system to help fight infections, notes WebMD.