Cough is a common symptom of allergy. It could be due to nasal allergy or an early sign of asthma. Patients with nasal allergy often has post-nasal drip, which can cause chronic cough. Inhalation of the allergens into the airways can also cause itchiness of the throat leading to cough. Asthma is a common and early symptom of asthma in both adults and children. Many asthmatic patients only cough and do not wheeze, but asthma medications might provide relief from the coughing. Nasal allergy and asthma are commonly caused by allergens such as dust mites, animal dander, pollens and mould spores. Air pollutants such as suspended particles, sulphur dioxide, nitrogen dioxide and ozone can also worsen symptoms.
To evaluate patients with chronic cough, a thorough history should be taken to document environmental allergen exposure both at home and at work. Lung function test should be done to look for evidence of asthma. As asthma symptoms are intermittent, a normal lung function test cannot exclude the diagnosis. If in doubt, bronchial challenge test with an agent that can provoke asthma symptoms (methacholine, histamine, adenosine or mannitol), or the suspected allergen should be performed. Allergy testing with skin prick test or serum IgE test would identify the cause of the cough. Allergen avoidance is often very effective in relieving the symptoms without resorting to medications.
Many patients with chronic cough might be suffering from gastroesophageal reflux disease, especially if the patient already has asthma. If the symptoms respond poorly to allergy and/or asthma medications, a trial of anti-reflux treatment should be given.