Phlegm—often simply called mucus—is something most people notice only when they’re sick, congested, or dealing with allergies. But mucus plays an essential role in protecting your respiratory system every single day. It traps dust, allergens, viruses, and bacteria before they reach your lungs. Under normal circumstances, your body produces 1 to 1.5 liters of mucus daily, most of which you swallow without realizing it ( Cleveland Clinic, 2022).

However, certain conditions can cause your mucus to thicken, become excessive, or feel stuck in your throat and chest. When this happens, understanding the causes and knowing how to reduce buildup can greatly improve your comfort and breathing.