According to Everyday Health, swallowing mucus is harmless. Mucus, or secretions from the respiratory passages, allows the body to remove foreign objects from the airways and lungs. When mucus is swallowed, any pathogens present in mucus are quickly destroyed by stomach acids and enzymes, according to Focus Magazine.
When the body is healthy, mucus is thin and watery and is therefore commonly swallowed without notice, according to Blue Shield of California. The mucus keeps the nose and throat moist and helps to carry away bacteria and other foreign particles that cause irritation and infection.
Blue Shield also states that when a person has a cold, allergies or congestion, the amount, color and thickness of mucus increases substantially. While expelling mucus by blowing one's nose or by spitting it out gets rid of some of the excess, it makes little difference if it is expelled or swallowed. When using a tissue, dispose of the tissue promptly to prevent the spread of sickness to others.
Many people do not like the sensation of swallowing mucus and therefore do not. However, if swallowed, it is simply reabsorbed by the body, according to Everyday Health. The dirt, dust and other debris present in mucus is passed out of the body while any bacteria it contains is killed by stomach acid.