Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Cough ?
    ### Response:
    A cough is a natural reflex that protects your lungs. Coughing helps clear your airways of lung irritants, such as smoke and mucus (a slimy substance). This helps prevent infections. A cough also can be a symptom of a medical problem.
                
Prolonged coughing can cause unpleasant side effects, such as chest pain, exhaustion, light-headedness, and loss of bladder control.
    