Quick Answer
Seasonal allergies (hay fever) are caused by IgE-mediated immune reactions to airborne pollen — primarily from trees in spring, grasses in summer, and ragweed in fall. They affect 81 million Americans. Nasal corticosteroid sprays are the most effective first-line treatment; allergen immunotherapy is the only option that modifies the underlying disease long-term.
Key Takeaways
- Seasonal allergies are caused by IgE-mediated reactions to airborne pollen (trees, grasses, weeds) and outdoor mold spores
- Spring = tree pollen; Summer = grass pollen; Fall = ragweed (the most potent US allergen affecting 23 million people)
- Intranasal corticosteroid sprays are more effective than oral antihistamines for nasal congestion — now considered first-line
- Climate change has extended pollen seasons by ~20 days and increased pollen potency by up to 60%
- Allergen immunotherapy (allergy shots or SLIT) is the only treatment that modifies the underlying immune response
- See an allergist if OTC medications fail to control symptoms or symptoms interfere with daily life
Seasonal Allergic Rhinitis
Seasonal Pollen & Allergen Calendar — When Allergy Seasons Peak
Commonly referred to as "hay fever", allergic rhinitis affects millions globally. It is triggered by outdoor aeroallergens, primarily pollens from trees, grasses, and weeds, as well as outdoor mold spores. Understanding different pollen types is the foundation of effective avoidance.
Seasonal Timeline
- Spring: Tree pollen (birch, cedar, oak, pine).
- Summer: Grass pollen (timothy, Bermuda, orchard).
- Fall: Weed pollen (ragweed, nettle, mugwort).
- Winter: Generally a relief period for outdoor allergies, though indoor allergens may worsen. Mold allergies often spike with damp autumn leaves.
Geographic Variation
Your region dramatically affects your seasonal allergy burden. Our seasonal allergy regional guide maps the worst allergy cities and seasons by US geography. Meanwhile, climate change is extending pollen seasons by weeks, increasing the potency and geographic spread of allergenic plants.
Treatment Options
First-line therapies include intranasal corticosteroids and oral second-generation antihistamines. For severe, refractory cases, allergen immunotherapy (subcutaneous injections or sublingual tablets) provides long-term relief.