Why Los Angeles Has a Unique Allergy Problem
Los Angeles's allergy burden is shaped by three forces that don't combine anywhere else in the US. First, the Mediterranean climate — warm, dry summers and mild winters — means pollen never truly stops. Unlike Chicago or New York where sub-zero winters provide months of genuine relief, greater LA's coldest months still allow significant allergen production from year-round grasses and some tree species. Second, Los Angeles has a complex and largely imported ornamental tree portfolio — olive, sycamore, eucalyptus, and jacaranda planted extensively across the region for decades — many of which are highly allergenic and produce pollen for unusually long seasons. Third, the Santa Ana wind events that bring dry, hot air from inland desert areas also sweep pollen across the basin in concentrated episodes that can spike counts dramatically.
Los Angeles Monthly Pollen Calendar
LA's Defining Allergens
Olive Trees — The Dominant Spring Allergen
Olive trees were planted throughout Southern California for decades — lining streets, filling parks and yards — because of their drought tolerance and Mediterranean aesthetic. The consequence: massive concentrations of highly allergenic olive pollen every spring. LA now restricts new olive tree plantings in many municipalities, but millions of existing trees continue to produce pollen from February through May. March is olive peak, and for olive-sensitized individuals, it's the worst period of their entire allergy year.
Sycamore (London Plane Tree)
London plane trees — sycamore hybrids — line thousands of miles of LA streets and are one of the most common urban trees in the basin. They produce fine, powdery pollen in spring and year-round tiny seed hairs (called achenes) that, while not true pollen, can cause significant respiratory irritation and allergic reactions. Sycamore is a significant but often unrecognized allergen for LA residents.
Eucalyptus
Eucalyptus trees are ubiquitous throughout Southern California. Unlike olive and sycamore, eucalyptus is primarily a fragrance and volatile compound irritant rather than a protein allergen — it can trigger non-allergic rhinitis and airway irritation, particularly in people with asthma or existing airway sensitivity, even in people who don't have true eucalyptus IgE sensitization.
Bermuda Grass — Year-Round
LA's warm climate means Bermuda grass never fully goes dormant. While counts are lower in December and January, grass pollen is a year-round contributor to LA's allergen burden. May through August represent peak grass season with the highest counts, but there's rarely a month when grass pollen is entirely absent from the LA basin.
The Santa Ana Wind Effect
Santa Ana winds — hot, dry offshore winds that blow from inland desert areas into the LA basin — are one of the most distinctive weather events in Southern California. For allergy sufferers, they're doubly problematic. They carry concentrated pollen from inland agricultural and native vegetation areas into the urban basin, creating acute pollen spikes. They also carry fine dust, particulate matter, and fire smoke during fire season, which inflames airways and amplifies allergic reactivity. A Santa Ana event during olive or grass season can produce the worst allergy days of the year — far exceeding what ambient pollen counts would suggest.
Westside vs Inland LA Variation
The coastal influence creates meaningful variation in allergy conditions across the LA basin. Westside neighborhoods — Santa Monica, Venice, Culver City, West Hollywood — benefit from marine air and coastal fog that can suppress pollen counts relative to inland areas. San Fernando Valley, Pasadena, and Pomona experience higher temperatures and less marine influence, which typically means higher pollen concentrations during peak season. On Santa Ana days, this gradient reverses — inland-origin winds push higher pollen toward the coast.
Track LA's unique allergen profile daily.
Anthos monitors olive, sycamore, grass, and more — giving you the species-specific data that matters for LA's one-of-a-kind allergen environment.
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Anthos provides general wellness information only. Nothing in this article constitutes medical advice, diagnosis, or treatment. Always consult a licensed healthcare professional before making health decisions.