What are atopic diseases?
Atopic diseases are a group of medical conditions characterized by an overactive immune system response to normally harmless substances, such as pollen, dust, animal dander, or certain foods. These conditions, grouped under the term "atopy," primarily include atopic eczema, allergic rhinitis, allergic conjunctivitis, and allergic asthma. They often appear in childhood but can persist into adulthood. The common factor in these diseases is an exaggerated immune response, which causes various symptoms affecting the skin, respiratory tract, and mucous membranes.
1. The basics of atopy: genetic predisposition and environmental factors
A genetic predisposition plays a crucial role in the development of atopic diseases. If a parent is atopic (meaning they suffer from one or more atopic diseases), the child's chances of developing atopy increase significantly. However, this genetic susceptibility alone is not enough to explain the onset of symptoms. Environmental factors are added to this predisposed background to promote the appearance of these diseases.
Among environmental factors, we find exposure to allergens such as animal dander, dust mites, molds, pollen, but also air pollution and passive smoking. Modern lifestyles, with processed foods, increased hygiene, and reduced contact with nature, are often blamed as an indirect cause of the rise in atopic diseases. The hygiene hypothesis, for example, suggests that reduced exposure to infectious agents during early childhood alters the normal development of the immune system, thereby promoting inappropriate immune reactions.
2. Atopic eczema: an inflammatory skin disease
Atopic eczema, also known as atopic dermatitis, is one of the main atopic diseases. It is a chronic inflammatory skin disease that causes dry skin, intense itching, and the appearance of red patches sometimes accompanied by small weeping vesicles. This disease often begins in the first months of life and affects approximately 15 to 20% of children in industrialized countries.
Atopic skin is characterized by a defective skin barrier, which makes it more permeable to allergens and irritants. This leads to persistent inflammation, along with itching and skin rashes. The majority of atopic dermatitis cases appear in children, and although eczema often improves with age, some individuals will continue to suffer from it into adulthood.
Environmental factors can worsen atopic eczema, including climatic variations (dry air, cold, or excessive heat), irritating products like soaps or detergents, and allergens present in the environment (pollen, animal dander). Certain foods can also trigger flare-ups in people with atopic dermatitis, although this is more common in young children.
3. Allergic Rhinitis: Inflammation of the Upper Airways
Allergic rhinitis is another common atopic condition, marked by inflammation of the upper airways, especially the nose. It occurs in response to allergens such as pollen (hay fever), dust mites, pet dander, or mold. Symptoms include sneezing, a runny or blocked nose, nasal itching, and sometimes a loss of smell.
Allergic rhinitis is more common during certain times of the year, especially in spring and autumn, when pollen concentrations in the air are high. However, it can also be perennial for individuals continuously exposed to household allergens like dust mites or pets.
People with allergic rhinitis are often susceptible to other atopic conditions, including allergic asthma and allergic conjunctivitis. The link between rhinitis and asthma is well-established, as untreated nasal inflammation can worsen lower airway inflammation, triggering asthma attacks in sensitive individuals.
4. Allergic Conjunctivitis: Eye Inflammation
Allergic conjunctivitis is an inflammation of the conjunctiva, the membrane covering the white part of the eye and the inside of the eyelids. It is caused by an allergic reaction to substances like pollen, pet dander, or dust. Symptoms include red, itchy, burning, or watery eyes, as well as a feeling of a foreign object in the eyes.
Although benign, allergic conjunctivitis can be very uncomfortable and often interferes with daily activities. As with other atopic conditions, it is linked to an excessive immune response. It is frequently associated with allergic rhinitis, and people suffering from one of these conditions often develop the other.
5. Food Allergies: A Risk for Atopic Children
Food allergies are common in people with atopic dermatitis, especially young children. It is indeed frequent for a child suffering from atopic eczema to develop an allergy to a food, often within the first years of life. The most common food allergens are cow's milk, eggs, peanuts, tree nuts, fish, and shellfish.
The immune responses triggered by food allergies can lead to various reactions, ranging from skin symptoms (hives, eczema) to gastrointestinal issues (vomiting, diarrhea), and even severe reactions like anaphylaxis, which requires emergency medical attention.
Children with atopic dermatitis have an increased risk of developing food allergies, partly due to their impaired skin barrier. This allows food proteins to come into contact with the immune system through the skin, leading to sensitization.
6. The Evolution of Atopic Conditions Over Time
Atopic conditions often evolve over the years, in a phenomenon known as the "atopic march." This term describes the typical progression of atopic diseases, which generally begins with atopic dermatitis in infants, followed by the appearance of allergic rhinitis and allergic asthma as the child grows.
While some children with atopic eczema never develop other atopic conditions, many will develop a respiratory allergy like rhinitis or asthma during their lifetime. It is also possible for atopic symptoms to lessen over time, but some people will continue to suffer from these conditions into adulthood, even if the intensity of symptoms may decrease.
Regular medical follow-up and proper symptom management are essential to prevent complications and improve the quality of life for atopic patients. Treatment primarily involves avoiding allergens, using anti-inflammatory medications like corticosteroids, antihistamines to relieve symptoms, and in some cases, desensitization (immunotherapy).
7. Treatment and Management of Atopic Conditions
Cases of atopic dermatitis require appropriate medical care, especially when the condition is severe or resistant to usual treatments.
The first line of treatment involves the regular application of emollients to maintain skin hydration and repair the skin barrier. In cases of inflammatory flare-ups, topical corticosteroids or calcineurin inhibitors are often prescribed to reduce inflammation and soothe itching.
In some cases of severe atopic eczema, systemic treatments like immunosuppressants or biotherapies may be considered to control chronic inflammation. These treatments are generally reserved for the most severe forms of the condition, when topical treatments are no longer sufficient to manage symptoms.
For allergic rhinitis and allergic conjunctivitis, treatment primarily relies on antihistamines, which reduce the allergic reaction and associated symptoms. In some cases, nasal corticosteroids may be necessary to control inflammation of the upper airways. Allergen desensitization, or immunotherapy, may also be considered for patients with severe or persistent rhinitis. This treatment involves gradually exposing the patient to increasing doses of the responsible allergen to reduce the immune system's sensitivity.
Regarding food allergies, the main strategy remains strict avoidance of the responsible food, with increased vigilance to prevent cross-contamination. For patients at risk of anaphylaxis, prescribing an emergency kit containing adrenaline is essential.
Conclusion
Atopic conditions encompass a range of chronic inflammatory disorders that result from an exaggerated immune response to common substances in our environment. Atopic eczema is a common condition in children, but other conditions like allergic rhinitis, allergic conjunctivitis, and food allergies can also appear in atopic individuals.
Genetic predisposition, combined with environmental factors, plays a key role in the development of these conditions. Although symptoms can evolve over time, requiring adapted management at each stage of life, it is possible to effectively manage these disorders through specific treatments and a healthy lifestyle.
In conclusion, although atopic conditions can persist into adulthood, early and appropriate management often helps limit their impact on patients' quality of life and prevent long-term complications.