Allergisation

Allergisation is the process by which the immune system becomes sensitized to an otherwise harmless substance, known as an allergen, and develops an allergic response on subsequent exposures. It is a key mechanism in the onset of allergic diseases such as allergic rhinitis, asthma, atopic dermatitis, and many food allergies.

Mechanistically, allergisation typically begins with initial exposure that promotes a T helper 2 (Th2)–driven response and the production of allergen-specific IgE antibodies by B cells. These IgE molecules bind to high-affinity receptors on mast cells and basophils, creating a primed state. On later contact with the same allergen, cross-linking of bound IgE triggers degranulation and the release of mediators such as histamine, leukotrienes, and prostaglandins, producing symptoms. Some reactions are not IgE-mediated, but may involve other immune pathways and T cells.

Common allergen sources include inhalants (pollen, house dust mites, animal dander), foods (peanuts, tree nuts, milk, eggs, shellfish), insect venoms, and certain medicines. The course and severity of allergic sensitisation are influenced by genetic predisposition (atopy) and environmental factors, such as urban living, pollution, early-life microbial exposure, antibiotic use, and mode of birth. The timing of exposure, particularly in infancy, can affect the likelihood of sensitisation.

Prevention and management focus on avoiding known triggers when possible, controlling symptoms with medications, and in some cases immunotherapy, which may modify disease progression. The overall prevalence of allergisation and resulting allergic diseases has risen in many regions, prompting ongoing research into underlying causes and preventive strategies.