I. Definition of allergic reaction
Allergic reaction is a special kind of pathological immune reaction, which is manifested when the body receives a certain allergen through various ways such as inhalation, ingestion, injection or contact, which can lead to a strong reaction in a certain tissue or organ, or even systemic, causing various kinds of dysfunction or tissue damage. It is characteristic that this specific reaction to specific allergens only occurs in individuals with allergic constitution, and the substances causing allergy are harmless to the general population, such as eggs, pollen, etc.
Second, the mechanism of allergic reactions
The pathogenesis of allergic reactions is complex, and only one of the most important etiological theories is introduced below: the TH1/TH2 balance theory. First of all, we would like to introduce a very important substance that triggers allergic reactions, sIgE (specific immunoglobulin, also called specific IgE), which is a special allergic antibody produced in the body of allergic patients after exposure to allergens, and the IgE induced by each allergen is different and therefore specific. sIgE is the culprit of allergic reactions.
TH1 and TH2 are two subtypes of a type of lymphocyte in the body. When allergens come into contact with the body, TH2 lymphocytes proliferate in allergic individuals, leading to an increase in sIgE production and finally triggering an allergic reaction; whereas in normal humans, TH1 lymphocytes proliferate after exposure to allergens, inhibiting sIgE production and thus not triggering an allergic reaction.
The specific process of allergic reactions: When the body is exposed to allergenic substances, sIgE is produced in the body of those who are prone to allergies, and sIgE is absorbed on the surface of a type of reactive cell, the mast cell, in the body. When exposed to the allergen again, the mast cell-IgE conjugate will bind to the allergen, causing the mast cells to release many active substances, which then cause a series of changes in the nerves and blood vessels, causing allergic symptoms to occur. Normal people do not produce such IgE antibodies after being exposed to allergic substances, so no allergic reactions occur.
III. Epidemiology of allergic reactions
The World Allergic Organization (WAO) published the results of an epidemiological survey of allergic diseases in 30 countries on the first World Allergic Disease Day: Of the total population of 1.2 billion in these countries, 22% (250 million people) suffer from IgE-mediated allergic diseases, including allergic rhinitis, asthma, conjunctivitis, eczema, food allergy, drug allergy and severe allergic reactions.
In Western countries, the prevalence of allergic rhinitis and asthma has increased rapidly in the last 40 years. Epidemiological surveys of allergic diseases in the general population in Europe began at the beginning of the last century, and their prevalence was below 1% in the 1920s, but began to rise after the industrial revolution, and gradually increased from the 1950s to the 1980s, with a dramatic increase after the 1980s. The World Health Organization (WHO) estimates that about 150 million people worldwide suffer from asthma, with more than 50% of adults and at least 80% of children suffering from asthma triggered by allergic factors, and more than 180,000 people die from asthma each year. The epidemiological survey of allergic rhinitis shows that the incidence of allergic rhinitis is higher in Asia, with about 30% of adults suffering from this disease, while the incidence of allergic rhinitis is less than 10% in Nepalese children, about 35% in Hong Kong, and 10%-40% in Singapore. The latest survey shows that the incidence of allergic rhinitis in Wuhan is about 16%. The above shows that allergic diseases are closely related to the development of material civilization in society.
The prevalence of food allergy, eczema and drug allergy has also increased significantly in recent years. In the United States, 3 million people are allergic to peanuts and nuts, and the prevalence of food allergy is 4% in children under 6 years old and 1% to 2% in adults. Atopic dermatitis is common among infants and children in Europe, the United States and developed regions of Asia and the Pacific, and its incidence has increased from 3% in the 1960s to 10% in the 1990s. Drug allergy accounts for 10% of all adverse drug reactions in the United States, and penicillin is the most common cause of sensitization, with 400 deaths per year due to penicillin anaphylaxis.
Fourth, the impact of the onset of allergic reactions factors
1.Physique: also known as genetic factors
Allergic constitution is the intrinsic factor that causes allergic reactions. Allergic diseases have obvious heredity. In general, both parents have allergic diseases, the incidence of allergic reactions in children is about 70%; one parent has obvious allergies, the incidence of allergic reactions in children is about 40%. The mother’s allergies have a more significant impact on the occurrence of allergic diseases in children than the father.
2, environmental factors.
(1) Environmental allergens: is one of the decisive factors in triggering allergic reactions. Clinical manifestations of allergic reactions are closely related to the environment, as many people know: some patients have very serious symptom attacks in northern cities, while symptoms can disappear completely in the south in Guangzhou, Shenzhen and other places; some patients are just the opposite. Some patients’ symptoms start to flare up in the spring or autumn, while in other seasons there is nothing unusual. These are due to the different allergens in the air in different environments.
(2) Change in hygiene: There is an important hypothesis in the development of allergic diseases, namely the “hygiene hypothesis”. The hypothesis is that children rarely suffer from bacterial infections from a young age due to an excessively clean environment, which does not effectively stimulate the body’s TH1 immune response capacity and makes the TH2 immune response capacity relatively stronger, thus leading to the susceptibility to allergic diseases.
(3) Dietary structure change: Nowadays, many children’s eating habits and dietary structure are gradually “westernized”, as well as some children’s “eutrophic state” and the occurrence of excessive obesity, all of which are unfavorable factors that can lead to the development of allergic diseases.
3. Bio-rhythmic factors.
The clinical manifestations of many allergic diseases have obvious biological rhythms, and many allergic diseases occur in the evening and early morning at dawn, while they can be asymptomatic or relatively light during the day. This is due to the change of autonomic function during the alternation of sleep and waking periods.
4.Other factors
Including the patient’s mental, emotional, physical strength, women’s menstrual flow, etc., may have some influence on the occurrence of allergic reactions.
Some people use a “balance theory” to explain and describe the onset and non-onset of allergic reactions: when the causative factors are less than the controlling factors, the state of non-onset is shown; when the causative factors > the controlling factors, the state of onset is shown; when therapeutic interventions are applied to strengthen the controlling factors, the state of non-onset is shown again.