The primary function of mucus in the respiratory system is to trap particles, including dust, microbes, and other foreign substances, preventing them from entering the lungs. Mucus also acts as a protective barrier, keeping the respiratory tract moist and aiding in the clearance of contaminants through ciliary action. This mucosal defense mechanism is vital for maintaining respiratory health and preventing infections. Additionally, it plays a role in the olfactory process, supporting the sense of smell.