How Do Allergies Develop Over Time?

The Sensitization Process: How Allergies Begin

Allergy development begins with sensitization — the immune system's first encounter with an allergen that results in production of allergen-specific IgE antibodies. During sensitization, antigen-presenting cells process allergen proteins and present them to naive T helper cells, which differentiate into Th2 cells. These Th2 cells release cytokines (particularly IL-4 and IL-13) that stimulate B cells to produce IgE antibodies specific to that allergen.

The IgE antibodies produced during sensitization travel through the bloodstream and bind to high-affinity IgE receptors on the surface of tissue mast cells and circulating basophils. The person is now sensitized — armed with allergen-specific IgE — but has no symptoms yet. Symptoms only appear when the allergen is encountered again and crosslinks the bound IgE on mast cells.

This sensitization process can occur silently over months or years of low-level allergen exposure. Individuals may be sensitized to dust mites, pet dander, or pollen for years without knowing it, until exposures intensify or the sensitization threshold is crossed.

The Atopic March: How Allergies Evolve During Childhood

The atopic march describes the typical sequence of allergic conditions in genetically predisposed children. It typically begins in early infancy with atopic dermatitis (eczema) and food allergy, particularly to milk and egg. As the skin barrier is disrupted in eczema, allergen proteins penetrate the skin and drive systemic sensitization — explaining why eczema is a risk factor for food allergy.

By toddler age, many atopic children develop asthma as airways become sensitized to environmental allergens. Allergic rhinitis — typically from pollen, dust mites, and pet dander — tends to emerge in middle childhood as cumulative allergen exposure builds. Not all children progress through every stage, and early interventions (emollient therapy, early food introduction) can interrupt the march.

Can Adults Develop Allergies for the First Time?

Yes. Adult-onset allergies are common and well-documented. Shellfish allergy is the most prevalent food allergy in adults and frequently develops in people who previously ate shellfish without issue. Tree nut, finfish, and sesame allergies also commonly first appear in adulthood. Adult sensitization may be triggered by relocating to a new region with different pollen, acquiring a new pet, starting a new job with occupational allergen exposure, or changes in immune function.

Hormonal changes, pregnancy, significant illness, stress, and alterations in gut microbiome composition have all been proposed as factors that can destabilize immune tolerance in adults and promote new sensitization. The mechanisms underlying adult-onset allergy are not fully understood but likely involve loss of pre-existing immune tolerance rather than truly 'first-time' sensitization.

Can Allergies Go Away Over Time?

Some allergies resolve naturally over time. Milk, egg, wheat, and soy food allergies outgrown in childhood in approximately 60–80% of children by adolescence. The resolution appears linked to the development of oral tolerance — regulatory T cell-mediated immune suppression of the Th2 response. Regular consumption of the food while tolerating it (baked milk, cooked egg) may accelerate tolerance development.

Peanut allergy is outgrown in approximately 20% of cases. Tree nut and shellfish allergies rarely resolve spontaneously. Environmental allergies — to pollen, dust mites, and pet dander — tend to persist throughout life without treatment, though symptom severity can fluctuate. Allergen immunotherapy can accelerate tolerance and produce long-lasting disease modification.