What causes seasonal allergies to flare up each year?

Seasonal allergies flare up each year because airborne pollen from trees, grasses, and weeds triggers an overactive immune response in sensitive individuals, causing the body to release histamine and other inflammatory chemicals that produce allergy symptoms.

According to the American Academy of Allergy, Asthma & Immunology, the primary culprits behind seasonal allergic rhinitis include tree pollen in spring (March through May), grass pollen in late spring and summer (May through July), and ragweed pollen in fall (August through October). Each allergen has distinct peak seasons, which explains why some people experience symptoms at different times throughout the year.

The immune system mistakenly identifies harmless pollen proteins as dangerous invaders. When exposed to these allergens, specialized immune cells called mast cells release histamine, leukotrienes, and other inflammatory mediators. This cascade reaction causes the characteristic symptoms of sneezing, runny nose, itchy eyes, and nasal congestion that define seasonal allergies.

Weather patterns significantly influence pollen production and distribution. Warm, dry, and windy conditions increase pollen counts and spread allergens over wider areas. Conversely, rain temporarily reduces airborne pollen by washing it from the air and surfaces. Climate change has extended pollen seasons and increased overall pollen production, making seasonal allergies more severe and prolonged than in previous decades.

Geographic location plays a crucial role in determining which allergens trigger symptoms. For example, mountain cedar dominates winter allergen profiles in Texas, while birch pollen causes spring symptoms in northern states. Ragweed thrives in the eastern and midwestern United States, affecting millions during autumn months.

Individual genetic factors influence allergy development and severity. People with family histories of allergies, asthma, or eczema have higher risks of developing seasonal allergies. The hygiene hypothesis suggests that reduced early childhood exposure to diverse microorganisms may contribute to increased allergy susceptibility in developed countries.

Cross-reactivity between certain foods and pollens can worsen seasonal allergy symptoms. This phenomenon, called oral allergy syndrome, occurs when proteins in fresh fruits and vegetables resemble pollen proteins, triggering additional allergic reactions in sensitive individuals.

Managing seasonal allergies effectively requires understanding personal trigger patterns and implementing appropriate prevention strategies, including monitoring local pollen forecasts and considering allergy medications or immunotherapy treatments.

Related: Allergies & Immune System · When should allergy symptoms be checked by a doctor? · Can allergies cause fatigue and brain fog? · Why are some allergy symptoms worse in the morning?