CA · Allergy Season Guide
California Allergy Season Guide
California experiences a Mediterranean climate with mild, wet winters and warm, dry summers along the coast, with hotter inland valleys.
Summary
California has 0 active PollyMap collection sites, and is seeking partners in 11 additional cities. Tree pollen typically dominates early spring, grass pollen peaks in late spring and early summer, and weed pollen (including ragweed) extends from late summer through fall.
PollyMap collection status across California
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- Pollen from local trees, grasses and weeds
- Airborne mold spores
- Dust mites and other indoor allergens
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Statewide allergy overview
California experiences a Mediterranean climate with mild, wet winters and warm, dry summers along the coast, with hotter inland valleys.
Oak, olive, cypress, and acacia tree pollen are the largest spring triggers. Bermuda and rye grass extend the season into summer, and ragweed plus sagebrush are the late-summer weeds.
Coastal humidity supports year-round Cladosporium and Alternaria. Fall and winter rain events drive the strongest spore peaks.
Allergy patterns vary by elevation and proximity to coast or mountains within California, but most of the state shares a common seasonal rhythm of spring tree pollen, summer grass pollen, and late-summer to fall weed pollen.
California allergy calendar
Month-by-month intensity for the four major airborne allergen categories.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Tree | Mod | High | V.High | V.High | High | Mod | Low | Low | Mod | Mod | Low | Low |
| Grass | Low | Low | Mod | High | V.High | High | Mod | Mod | Mod | Low | Low | Low |
| Weed | Low | Low | Mod | Mod | Mod | High | High | V.High | V.High | High | Mod | Low |
| Mold | Mod | Mod | Mod | Mod | Low | Low | Low | Low | Mod | High | High | Mod |
Seasonal focus · Oct–Dec
October–December in California
California's mild climate means there is no true pollen off-season. Fall brings ragweed and sagebrush in inland valleys, lingering grass pollen along the coast, and mold spores that spike with the first fall rains — especially in Northern California as the rainy season begins.
By December, much of the state sees lower pollen, but the coast and Southern California stay mild enough that something is always in the air. In the Central Valley and around Los Angeles and San Diego, winter rains trigger mold, and some trees begin pollinating by January.
Top airborne molds
Major city guides in California
CA
Los Angeles
View Los Angeles allergy season guide →
CA
San Diego
View San Diego allergy season guide →
CA
San Jose
View San Jose allergy season guide →
CA
San Francisco
View San Francisco allergy season guide →
CA
Fresno
View Fresno allergy season guide →
Latest PollyMap reports for California
Frequently asked questions
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