Dr Sudip Chowdhury, Senior Paediatric Consultant at Manipal Hospital, Gurugram explained that pneumonia involves alveolar infection that disrupts oxygen exchange, often indicated by dark-coloured expectoration, sustained fever and dyspnoea. “Unlike a regular cold, where your cough fades in a few days, pneumonia often brings a wet cough with yellow or green mucus that sticks around," he added.