What it does benylin mucus cough works to thin and loosen chest mucus making it easier to cough up how it works active ingredient guaifenesin helps to thin and loosen mucus in your chest making it easier to cough up whilst levomenthol also helps relieve congestion making it easier for you to breathe what is a mucus cough when mucus builds up in the chest it can be hard to get rid of by coughing so itrsquos helpful to have something to take to loosen the mucus and relieve the feel