Persistent or recurrent episodes usually last for more than a month, and some patients only have a cough at night, especially in the second half of the night, or in the early morning, or after exercise, with no clinical signs of infection and no obvious positive signs on physical examination. If the patient also has frequent “cold” symptoms without fever, such as sneezing, runny nose, itchy nose, itchy eyes, etc., it is especially important to pay attention to the presence of allergic cough if there is a history of personal allergies, such as eczema, during infancy and childhood. As with any allergic disease, another great characteristic of allergic cough is that it can recur with changes in climate, environment, lifestyle, etc., and is difficult to heal! Antibiotics or cough suppressants and expectorants are ineffective. The formation and recurrence of a cough is often the result of a combination of many complex factors. 1. Inhalants. Inhalants are divided into two types: specific and non-specific. The former are dust mites, pollen, fungi, animal dander, etc.; non-specific inhalants such as sulfuric acid, sulfur dioxide, chloramine, etc. Occupational cough specific inhalants such as toluene diisocyanate, phthalic anhydride, ethylenediamine, penicillin, protease, amylase, silk, animal dander or excrement, etc. In addition, non-specific still have formaldehyde, formic acid, etc. 2. Infection. The formation and onset of cough is associated with recurrent respiratory tract infections. In patients with cough, there can be specific IgE of bacteria, viruses, mycoplasma, etc., which can stimulate coughing if the corresponding anti-principles are inhaled. In viral infections, direct damage to the respiratory epithelium can occur, resulting in increased respiratory reactivity. It has been suggested that interferon and IL-1 produced by viral infections increase histamine release from basophils. In the lactation period, there are also many cases of coughing after infection with respiratory viruses (especially respiratory syncytial virus). Cough caused by parasites such as roundworms and hookworms can still be seen in rural areas. 3. Food. Cough attacks due to diet are often seen in cough patients, especially in infants and young children who are prone to food allergies, but this decreases with age. The most common foods that cause allergies are fish, shrimp and crabs, eggs, milk, etc. 4. Climate change. Cough can be triggered when the temperature, barometric pressure and/or ions in the air change, so there is more incidence in the cold season or in autumn and winter when the climate changes. 5. Mental factors. The patient’s emotions, nervousness and anger can trigger a cough attack, which is generally thought to be caused by the cerebral cortex and vagal reflexes or hyperventilation. 6. Exercise. About 70% to 80% of patients with cough induce cough after strenuous exercise, which is called exercise-induced cough, or exercise cough. Clinical manifestations include cough, chest tightness, shortness of breath, and wheezing, and croup can be heard on auscultation. In some patients, although there is no typical asthma manifestation after exercise, bronchospasm can be detected by pulmonary function measurements before and after exercise. 7. Cough and drugs. Some medications can cause coughing attacks, such as insulin, which causes coughing due to blocking β2-adrenergic receptors.