Introduction to Allergy

• Atopy is the tendency to produce an exaggerated immunoglobulin E (IgE) immune response to otherwise harmless substances in the environment
• Sensitization is the development of IgE antibodies to allergens that are ingested, absorbed or inhaled
• Allergies, also known as allergic diseases, are conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment
• Allergies include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis
• Allergens are proteins or chemicals bound to proteins against which individuals make IgE antibodies
• Asthma, allergic rhinitis, hay fever, atopic dermatitis, and food allergy are considered atopic diseases
• Some individuals with elevated total and specific IgE levels may not show any signs of illness
• Asthma, atopic dermatitis, and hay fever are complex diseases influenced by genetic and environmental factors
• The prevalence of asthma and allergies has increased, but the trend seems to have plateaued in High-Income Countries (HIC) versus Low- and Middle-Income Countries (LMIC)
• About 20 million South Africans suffer from allergic respiratory diseases
• Environmental risk factors for allergic diseases include air pollution, environmental tobacco smoke, water hardness and dampness, nutrition, allergen exposure, family size, infections, and hygiene, as well as gene-environment interactions
• Natural history studies of allergic diseases and asthma are fundamental for predicting disease onset and prognosis
• The "allergic march" in childhood starts with early onset of atopic dermatitis and food allergies in infancy, progressing to asthma, allergic rhinitis, and inhalant allergen sensitization in later childhood
• Allergy and asthma of earlier onset and greater severity are associated with disease persistence
• The allergic march of childhood begins with the highest incidence of atopic dermatitis and food allergies in the first 2 years of life
• Infants rarely show allergic symptoms in the first month of life, but by 3 months of age, atopic dermatitis, food allergies, and wheezing problems become common
• Early food allergen sensitization is a significant risk factor for food allergies, atopic dermatitis, and asthma
• Allergic airways diseases typically start slightly later in childhood, with childhood asthma often manifesting with lower respiratory tract infections or bronchiolitis episodes in the first few years of life
• Allergic rhinitis begins in childhood and is paralleled by a rise in inhalant allergen sensitization
• Perennial inhalant allergen sensitization emerges between 2 and 5 years of age, while seasonal inhalant allergen sensitization becomes apparent slightly later (ages 3-5 years)
• Allergy and asthma prevention strategies can be primary (preventing allergy/asthma inception), secondary (preventing persistent asthma), or tertiary (preventing asthma exacerbations)
• Preventive measures include microbial supplementation, prevention of the allergic march, early-life elimination of allergenic foods (cow’s milk, peanut, egg, fish), and breastfeeding for 4-6 months