 [ Symptoms ] what is the difference between staph and impetigo [ Disease ] the indicative sign of getting better is the cough intensity and frequency the fever…but for the mucus what happens is your immune system sends white blood cells called neutrophils rushing to the area these cells contain a greenish colored enzyme and in large numbers they can turn the mucus the same color but if the mucus is turning greenish and thicker while the fever and cough is getting bad then you need to see a doctor as it might be due to chest infection re arising…or has become resistant to antibiotics