Today is World Allergy Day, a day established by the World Allergy Organization (WAO) precisely because allergic diseases are becoming a global public health problem that requires more attention and focus from governments, medical groups and doctors and patients. In both developed and developing countries, various allergic diseases including asthma, allergic rhinitis and conjunctivitis, drug allergy, food allergy, insect bite allergy, skin eczema (atopic dermatitis), urticaria or severe systemic allergic reactions (anaphylaxis) are affecting people’s health and daily life to varying degrees, and in some severe cases even life-threatening. The manifestations of “allergies” are diverse and can affect many organs of the body. Nose allergies (allergic rhinitis) are seen in ENT, asthma in respiratory medicine, skin allergies (eczema, urticaria) in dermatology, and food allergies in infants and children in pediatrics. Sometimes allergic diseases occurring in different organs are intrinsically related to each other. Skin eczema and food allergies in infancy may be related to rhinitis and asthma in adulthood, so controlling eczema in infancy will reduce the risk of allergic rhinitis and asthma in adulthood. Why do allergic diseases occur? Genetic factors are the basis for the occurrence of allergic diseases. Genetic factors are commonly referred to as “allergies”, and doctors often ask allergy sufferers if there are other people in their family who have allergies. But even if there is a hereditary allergy, not all of them will get allergic diseases. For example, piles of hay can easily catch on fire, but they don’t necessarily catch on fire; whether or not they do depends on the weather, fire prevention measures, and so on. So a family, may all have inherited allergies, but not everyone will develop allergic diseases. What are the other factors that promote allergic diseases? Allergens are the most well known cause. However, it is important to know that not all patients with allergic diseases are related to allergens. For example, in patients with atopic dermatitis (eczema), roughly 30% of patients tested for IgE antibodies to allergens are all negative. A patient cannot be allergic to all allergens; for example, an allergy to peanuts only requires avoidance of peanuts, not all high-protein foods. Allergies to certain foods in infancy and early childhood, such as milk and eggs, will be tolerated as the body grows older and will not be allergic to them when they grow up. Environmental factors are a relatively easy cause to overlook Environmental factors here refer to indoor or outdoor environmental pollution. Studies have found that pollutants in the atmosphere may be related to the development of asthma, and some studies in recent years have also found that indoor pollutant formaldehyde may be related to the development of atopic dermatitis. Common indoor and outdoor pollutants are listed in the table below. Climate, lifestyle, etc. also have an impact Changes in climate can affect the distribution of allergens in the environment, influence the concentration of pollutants in the air, and change the temperature and humidity to induce exacerbation of allergic diseases. The common skin eczema may flare up in the hot and humid summer months, or it may worsen in the winter due to a drop in air humidity and dry skin. Modern lifestyles also contribute to the development of allergic reactions. For example, the occurrence of skin eczema is related to the fact that modern people take excessive baths to destroy the skin barrier and do not protect their skin and apply moisturizers in time. The fact that people living in cities are more prone to allergic diseases than those living in the countryside may be related to the lack of diverse microorganisms in the urban living environment to stimulate the balanced development of the immune system. People living in big cities, who often stay up late, work under stress, and eat unhealthily, can also induce aggravation of allergic diseases. This is why people with allergic diseases need a healthy lifestyle even more.