Asthma is not contagious, so is it hereditary? This is a question that is often asked by patients and their relatives, and one that we often have to answer. Asthma is an obvious genetic disease that runs in families, but it is a “polygenic disease” and environmental factors also play an important role, so genetics only determines the person’s allergy, i.e. whether they are prone to allergic reactions to various environmental factors and whether they are susceptible to asthma. The “susceptibility” to various allergens is a key factor in the development of asthma and is an internal factor, but not the only factor in the development of asthma. Environmental factors, such as allergens and triggers, must also be present to cause asthma. Asthma is actually an allergic (i.e., allergic) inflammatory disease that occurs primarily in the airways, and the allergic reaction is caused by abnormal immune function. Many phenomena suggest that allergic diseases are closely related to genetics, and asthma is certainly closely related to genetics. Many patients with allergies (or atopy) have a much higher chance of having first-degree relatives with various allergic diseases (including allergic asthma, allergic rhinitis, hay fever, infantile eczema, urticaria, etc.) than other family members without allergies. In the case of asthma, the family history is also known, and many grandchildren and even four generations have had patients with asthma. The author once conducted a questionnaire survey on 150 diagnosed asthma patients with a total of 1,775 members in three generations, and the prevalence of asthma was as high as 18.3%, close to 20 times that of the general population. The prevalence of asthma in foreign families has also been reported to be as high as 20% to 45%. Genetic factors play a very important role in the development of asthma, but not all people with genetic factors will develop asthma. Therefore, it can only be assumed that genetic factors contribute to the “potential” development of asthma in an allergic or atopic body. The role of environmental factors, such as inhalation of various allergic substances (allergens), respiratory viral and bacterial infections, smoking and air pollution, and other exogenous factors cannot be ignored. The latter often play a triggering and contributing role in the onset and exacerbation of asthma, making the condition worse. Therefore, efforts to reduce or avoid the role of various undesirable external factors that may trigger asthma are important in preventing asthma attacks and reducing the symptoms of attacks, such as cleanliness and hygiene in the living room, living and working environment, quitting smoking, active prevention and timely treatment of respiratory tract infections, etc., which should not be neglected in the comprehensive prevention and treatment of asthma. Since asthma has a genetic factor, do asthma attacks occur soon after birth? Not necessarily, the pattern is not very clear. The next generation can develop asthma in infancy after birth, or in adulthood, or in the third generation, which is called intergenerational inheritance. The author treated a patient with asthma whose daughter had only allergic rhinitis symptoms and denied any asthma symptoms, but airway excitation and diastolic tests showed significant airway hyperresponsiveness. After about six months, she had an asthma attack due to a cold, and croup could be heard at the base of the lungs. This suggests that the patient’s daughter had occult asthma before the asthma attack.