Under normal circumstances, the detoxification function of the nasal cavity ensures that the above bacteria do not exceed the amount that the human body can withstand. When encountering inducing factors such as catching a cold, getting caught in the rain, or excessive fatigue, the detoxification function of the nasal cavity decreases, allowing the aforementioned bacteria to remain in the nasal cavity for a long time and reproduce in large quantities, thereby causing a cold. If the inflammation caused by a cold persists for a long time, it is prone to worsen into rhinitis. The main pathogenic factors of rhinitis are as follows:
(I) Genetic Factors
Individuals with a family history of allergic reactions are more susceptible to this disease. Most families of patients have histories of asthma, urticaria, or drug allergies. In the past, these patients were referred to as atopic individuals, whose ability to produce IgE antibodies exceeds that of normal people. However, in recent years, some authors have found that there is no significant difference in incidence between twins and the general population.
(II) Nasal Mucosa Susceptibility
The susceptibility originates from the constant stimulation of antigenic substances, but its degree depends on the number of mast cells and basophils in the nasal mucosal tissue and their ability to release chemical mediators. It has now been confirmed that the number of these cells in the nasal mucosa of patients with allergic rhinitis is not only higher than that of normal people, but they also have a stronger ability to release chemical mediators.
(III) Antigenic Substances
Antigenic substances that stimulate the body to produce IgE antibodies are called allergens. When these allergenic substances re-enter the nasal mucosa, they combine with the corresponding IgE to cause an allergic reaction. The allergens that cause this disease are divided into two major categories based on how they enter the human body: inhalant and food allergens.
1. Inhalant Allergens
Inhaled through breathing into the nasal cavity. These allergens mostly float in the air.
(1) Pollen Not all plant pollens can cause the disease. Only those with large amounts of pollen, wide vegetation coverage, strong allergenicity, and spread by wind are most likely to become allergens. Due to differences in vegetation species, the allergenic pollens vary in different regions. For example, birch and timothy grass pollen dominate in Northern Europe; ragweed dominates in North America; cedar tree pollen dominates in Japan; China's vast territory has inconsistent sensitizing pollens across regions, with wild wormwood pollen being predominant in northern areas. However, ragweed has been found both north and south of the Yangtze River, which should be taken seriously. In recent years, some people believe that with the continuous development of industrialization, the concentration of harmful substances like sulfur dioxide in the air increases, causing the protein structure on the surface of airborne pollen to mutate, making originally non-allergenic pollen highly allergenic. This may be one of the main reasons for the significant increase in the incidence rate. The types and content of pollen in the air show significant seasonality, with peaks in spring and summer-autumn.
(2) Fungi Distributed widely in nature, mainly found in soil and decaying organic matter. Both their mycelium and spores have allergenic properties, but the spores are stronger. Spores can spread widely through the wind, sometimes exceeding the amount of pollen in the air, with rural areas having higher concentrations than urban areas. The most common fungal species are Cladosporium, Alternaria, Penicillium, Aspergillus, and yeast. Cladosporium and Alternaria have significant seasonality, with their spore peaks mostly occurring in summer. High indoor temperatures and dampness promote fungal growth. The soil in indoor flower pots also often becomes a good growth environment for fungi.
(3) House Dust Mites Belonging to the class Arachnida of the phylum Arthropoda. Adult mites generally range in size from 300 to 500 μm. They mainly parasitize in various corners of living quarters, with the most found in dust inside mattresses, pillows, sofa cushions, etc. Mite excrement, eggs, shed skin, and fragmented limbs can all become allergens.
(4) Animal Dander One of the strongest allergens. Sensitive individuals who have prolonged contact with relevant animals can become sensitized. After sensitization, even small amounts of dander can trigger nasal symptoms. The animal dander that causes respiratory allergies mainly comes from animals closely associated with humans, such as pet dogs and cats, domestic dogs, cattle, horses, and sheep. The author once encountered a pathology lab technician who would sneeze upon contact with experimental animals like guinea pigs, followed by a large amount of clear mucus and mild asthma.
(5) Feathers Feathers from poultry or bedding, pillows, and clothing, as well as feathers shed by pet birds, can all be allergens.
(6) Indoor Dust A common allergen substance that causes perennial rhinitis. Its composition is quite complex, a mixture of various substances, including animal, plant, and chemical materials.
2. Ingested Allergens
Refers to allergenic substances that enter the body via the digestive tract and cause nasal symptoms. Their mechanism of action on the nasal mucosa is very complex and still not fully understood. Milk, eggs, fish and shrimp, meat, fruits, and even certain vegetables can all become allergens.
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