Benylin Children's Chesty Coughs is a clear colourless syrup. •What it does: Chesty coughs are caused by a build-up of mucus. BENYLIN® Children’s Chesty Coughs contains guaifenesin which helps thin and loosen mucus, and provides effective relief without causing drowsiness. •How it works: It is sugar free and comes in a strawberry flavour. Suitable for children from 6 years. •What is a chesty cough? Chesty coughs are caused by a build-up of phlegm and the cough mechanism kicks in to try and get rid of this excess phlegm to get it out of the body.