Both caffeine and alcohol dehydrate your body and since you are already losing fluid from the body as mucus, you’re better off without these. Alcohol also prevents the immune system from functioning properly, prolonging the cough and cold in your body.
People suffering from cold and cough should avoid deep-fried foods as acid, lard, and omega-6 fatty acids present in them can make the body produce more mucus.
One should avoid eating spicy foods and high-fat foods because they cause throat irritation and provoke more coughing.
Foods that contain sugar increase the risk of inflammation and infection in the body, so people having a cold should temporarily avoid sweet foods.