When allergens enter your body, they trigger a complex immune response that leads to your allergy symptoms. Your immune system identifies harmless substances like pollen or pet dander as threats and launches a defensive chain reaction12. White blood cells produce antibodies called IgE that attach to allergens, which then signal mast cells and basophils to release histamine and other inflammatory chemicals34.

Histamine acts as your body's bouncer, working to expel the perceived invader1. It causes blood vessels to become leakier, allowing white blood cells and protective substances to reach the affected area56. This immune overreaction leads to the classic allergy symptoms: sneezing, runny nose, watery eyes, itching, and in severe cases, breathing difficulties78. While this response is beneficial for fighting actual threats like parasites, with allergies, it's an inappropriate reaction to substances that won't actually harm you62.

Genetics plays a significant role in determining who develops allergies, with heritability estimated between 50% and 84% according to twin studies1. If one parent has allergies, a child has a 30-50% chance of developing them; this risk jumps to 60-80% when both parents have allergies2. Family history remains one of the most reliable predictors of allergic disease despite technological advances in identifying specific genetic variants3.

The genetic basis for allergies is complex and involves multiple genes rather than a single mutation. The Human Leukocyte Antigen (HLA) system is particularly important, as variations in these genes affect how the immune system recognizes potential allergens4. Researchers have identified specific genetic regions like the ETS1 gene, which functions as a "dimmer switch" controlling immune cell responses5. Other studies have found that the chromosome 11q13 locus is associated with multiple allergic conditions, suggesting involvement in central allergy mechanisms6. Interestingly, some genetic transmission patterns show parental differences, with certain allergy-related traits being inherited primarily through maternal lines7.

Pollen is the primary culprit behind seasonal allergies, with trees, grasses, and weeds releasing tiny grains that trigger immune responses in sensitive individuals12. Pollen counts-measurements of pollen grains per cubic meter of air-provide valuable information for allergy sufferers, ranging from low (0-4.9) to very high (10-12)3. These counts fluctuate throughout the day, typically peaking in the morning and on warm, dry, windy days when pollen can travel for miles45.

Climate change has significantly worsened seasonal allergies by extending pollen seasons and increasing pollen production67. Warmer temperatures cause plants to bloom earlier and produce pollen longer, while increased carbon dioxide levels make pollen more allergenic89. Environmental pollutants compound the problem, as air pollution damages pollen's surface structure and enhances its allergenic properties69. Urban areas face additional challenges from landscaping choices that often include high-pollen-producing plants6. For allergy sufferers, monitoring local pollen forecasts and limiting outdoor exposure during peak times can significantly reduce symptom severity510.