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*Disclaimer: HeyAllergy® provides all clinical services furnished to patients in California, Florida, Texas, Illinois, Nevada, Pennsylvania. In New York, clinical services are furnished by Hey Allergy Medicine.
Real-time pollen data for Modesto — updated daily.
Modesto sits in the northern San Joaquin Valley, surrounded by one of the most productive agricultural regions on earth — and those millions of acres of orchards and farmland are a massive source of tree pollen. Almond orchards, which blanket Stanislaus County and surrounding areas, bloom explosively in February, producing clouds of pollen that commercial beekeeping operations are brought in to service. Walnut orchards are similarly extensive and pollinate from April through May, producing heavy wind-dispersed pollen loads. Valley oak, interior live oak, and blue oak are native to the San Joaquin Valley floor and surrounding foothills, producing dominant pollen loads from March through May. Mulberry trees are widely planted as ornamentals throughout Modesto's residential neighborhoods and are among the most allergenic trees in the region, pollinating from March through April. Elm, ash, cottonwood, sycamore, and willow contribute pollen during spring. Chinese pistache, commonly planted as a street tree, adds to the pollen burden. Olive trees are cultivated in the region and produce highly allergenic pollen from April through June. The flat, open terrain of the Central Valley allows tree pollen to travel vast distances on prevailing winds, meaning Modesto residents are exposed to pollen from orchards and forests miles away.
Grass pollen is one of the most significant allergens in the Central Valley. Ryegrass (both annual and perennial Italian ryegrass) is extremely common in pastures, roadsides, and disturbed areas throughout Stanislaus County. Bermuda grass is extensively planted in lawns, parks, and athletic fields across Modesto. Bluegrass, Timothy grass, orchard grass, and bent grass contribute additional pollen loads. Foxtail grass is particularly prevalent in the Central Valley — it grows aggressively in vacant lots, canal banks, agricultural margins, and disturbed soils throughout the region. Johnson grass, a large perennial grass considered a noxious weed in California, is common in agricultural areas and produces abundant allergenic pollen from late spring through fall. The Central Valley's hot, dry summer conditions create windblown grass pollen that combines with agricultural dust to produce some of the highest airborne allergen concentrations in California. Grass pollen season in Modesto extends from April through July, with peak concentrations in May and June.
Weed pollen extends the allergy season deep into fall in Modesto. Ragweed pollinates from August through October and is common in disturbed agricultural soils and vacant areas. Sagebrush, a native of the California foothills and valleys, produces significant pollen loads from August through November. Amaranth (pigweed) thrives in the hot, dry conditions of the San Joaquin Valley and is abundant along agricultural field margins, roadsides, and disturbed soils. Russian thistle (tumbleweed), lamb's quarters, dock, plantain, saltbush (atriplex), and wormwood contribute additional weed pollen. The agricultural landscape surrounding Modesto creates vast expanses of disturbed soil where weed species colonize aggressively between crop cycles. Orache (saltbush family) is common in alkaline soils throughout the Central Valley floor. The combination of hot temperatures, dry winds, and flat terrain means weed pollen disperses widely and remains airborne for extended periods.
Modesto's Mediterranean climate creates distinct indoor allergen challenges across seasons. Dust mites thrive in bedding, upholstery, and carpeting — while the Central Valley is dry outdoors during summer, indoor humidity from evaporative coolers (swamp coolers), which are widely used in Modesto homes as an energy-efficient alternative to refrigerated air conditioning, creates ideal dust mite habitat. Mold is particularly problematic during the wet winter season (November through April) when rainfall combined with tule fog creates persistent dampness. Agricultural mold spores from decomposing crop residue, compost, and post-harvest field waste become airborne during harvest and fall plowing operations. Alternaria, Cladosporium, Aspergillus, and Penicillium are common throughout the region. Pet dander is a significant year-round allergen, and cockroach allergen is present in older homes throughout the city.
Severity: Moderate to High
Modesto's allergy season begins earlier than many residents expect. Almond orchards — the dominant crop across Stanislaus County — bloom in February, producing massive pollen loads visible as pink and white blossoms stretching to the horizon. Elm and mulberry begin pollinating in late February and March. Oak pollen starts building in March. Tule fog, the dense radiation fog unique to the Central Valley, persists through January and into February — this cold, damp fog traps pollutants and mold spores near ground level but typically clears as almond bloom begins. Winter rainfall promotes mold growth in damp areas. The transition from fog season to bloom season happens rapidly, catching many residents unprepared.
Severity: High to Severe
Spring into early summer is Modesto's worst allergy period. Oak, walnut, and olive tree pollen overlaps with the peak of grass pollen season — ryegrass, Bermuda, Timothy, foxtail, and Johnson grass all peak between April and June. The Central Valley heats rapidly, with daytime temperatures reaching the 90s by May and exceeding 100°F by June. Hot, dry winds pick up pollen and agricultural dust from surrounding farmland and carry allergens across the valley floor. The flat, open terrain provides no natural barriers to pollen dispersal. The San Joaquin Valley's bowl-like geography — Sierra Nevada to the east, Coast Ranges to the west — traps airborne allergens in the basin. This is consistently the period when Modesto allergy sufferers experience the most severe symptoms.
Severity: Moderate to High
Summer brings extreme heat (regularly exceeding 100°F) and the beginning of harvest season. Almond harvest in August and September generates enormous dust clouds as mechanical shakers and sweepers process the crop — this agricultural dust contains fine particulate matter, mold spores, and organic debris that triggers respiratory symptoms in residents miles from the nearest orchard. Weed pollen rises sharply with ragweed, sagebrush, amaranth, and Russian thistle. Ozone levels peak during summer, and the San Joaquin Valley regularly records some of the worst ozone pollution in the nation during this period. Wildfire smoke from Sierra Nevada and Northern California fires frequently settles into the valley, creating hazardous air quality events that compound allergic symptoms. The combination of agricultural dust, weed pollen, ozone, and wildfire smoke makes summer a challenging season despite the absence of tree pollen.
Severity: Low to Moderate
Fall provides the closest approximation of allergy relief in Modesto, though late weed pollen from sagebrush and Russian thistle persists into November. Agricultural field burning — while being phased out in the San Joaquin Valley — and post-harvest plowing release mold spores and dust into the air during October and November. The return of tule fog in November and December traps pollutants near ground level and creates damp conditions that promote mold growth. Indoor allergens become more significant as residents close up homes against cold fog and rain. Mold growth accelerates in damp winter conditions. December through January is typically the lowest-pollen period, but indoor allergens and fog-trapped pollutants ensure there is no truly symptom-free season.
Modesto sits in what atmospheric scientists describe as a "bowl" — the San Joaquin Valley is flanked by the Sierra Nevada range to the east (peaks exceeding 14,000 feet) and the Coast Ranges to the west, with the Tehachapi Mountains closing the southern end. This geography traps airborne pollutants, pollen, agricultural dust, and wildfire smoke in the valley for extended periods. Temperature inversions — where warm air above seals cooler air below — are common in the San Joaquin Valley, particularly during winter and late summer, preventing vertical dispersion of allergens. Modesto residents breathe some of the most allergen-concentrated air in California not because local pollen production is necessarily higher than other regions, but because the valley geography prevents that pollen and particulate matter from dispersing. Running a HEPA air purifier in bedrooms and main living areas is essential year-round, not just during obvious pollen seasons.
Stanislaus County is one of California's top almond-producing counties, and almonds are the state's most valuable agricultural export. The almond harvest in August and September generates massive dust plumes as mechanical tree shakers knock almonds from branches, then sweepers collect them from the orchard floor. This process lifts fine particulate matter, mold spores (Alternaria and Aspergillus colonize almond hulls), and organic debris into the air. Research has shown that almond harvesting operations produce locally elevated PM2.5 levels that exceed federal health standards. If you live within several miles of almond orchards — which surrounds most of Modesto on multiple sides — keep windows closed during August and September harvest operations and run HEPA filtration. Check air quality forecasts daily during harvest season.
Tule fog is a dense radiation fog unique to the Central Valley, typically forming from November through February when cool, moist air settles into the valley under temperature inversions. During tule fog events, visibility can drop below 200 feet and the fog can persist for weeks. From an allergy perspective, tule fog traps pollutants, mold spores, and particulate matter near ground level — creating a concentrated layer of respiratory irritants that persists until wind or warming breaks the fog. Many Modesto residents notice that their congestion and respiratory symptoms worsen during extended fog events, even though pollen counts are low. This is the trapped-pollutant effect, and it compounds the impact of indoor allergens that dominate during winter months. Homes with good weatherization and HEPA filtration provide the best protection during fog season.
The San Joaquin Valley is particularly vulnerable to wildfire smoke because its bowl geography traps smoke that drifts down from Sierra Nevada and Northern California fires. During the catastrophic fire seasons of 2020 and 2021, Modesto experienced weeks of hazardous air quality as smoke from fires burning 50 to 200 miles away settled into the valley. Wildfire smoke contains fine particulate matter that penetrates deep into lungs, and it compounds the effects of existing pollen and agricultural allergens. For allergy sufferers, wildfire smoke events can trigger severe asthma exacerbations and allergic inflammation that persists for weeks after air quality improves. The combination of wildfire smoke with existing allergy sensitization creates a multiplicative effect — treating underlying allergies with immunotherapy reduces your overall inflammatory burden and improves resilience during smoke events.
Many Modesto homes use evaporative coolers (swamp coolers) instead of refrigerated air conditioning. Evaporative coolers work by pulling hot outdoor air through water-saturated pads, cooling the air through evaporation. While energy-efficient and effective in the Central Valley's dry heat, swamp coolers add significant humidity to indoor air and do not filter pollen or particulate matter the way sealed refrigerated AC systems do. The added indoor humidity creates ideal conditions for dust mite populations. If you use a swamp cooler and experience year-round nasal congestion, itchy eyes, or nighttime symptoms, dust mites thriving in the humidified indoor environment are a likely cause. Consider supplementing with HEPA air purifiers in bedrooms, and use allergen-proof mattress and pillow encasements.
HeyAllergy provides telemedicine appointments with board-certified allergists and immunologists licensed in California. Book a virtual consultation from your Modesto home, have allergy blood tests ordered at a convenient local lab, and receive a personalized treatment plan targeting the specific Central Valley allergens driving your symptoms — whether oak, almond, ryegrass, ragweed, mold, dust mites, or agricultural particulates. HeyPak sublingual immunotherapy drops ship directly to your door and treat the root cause of allergies by building immune tolerance to your triggers over time. Most patients notice improvement within 3 to 6 months. Starting at $47 per month. HeyAllergy accepts Medicare and most major PPO health plans.
April through June is typically the worst period, with overlapping tree pollen (oak, walnut, olive, mulberry), peak grass pollen (ryegrass, Bermuda, foxtail, Johnson grass), and rising agricultural dust. August through September brings almond harvest dust and weed pollen. The San Joaquin Valley's bowl geography concentrates all airborne allergens in the basin.
The most common allergens in the Modesto area are oak, walnut, almond, mulberry, ryegrass, Bermuda grass, foxtail, ragweed, sagebrush, amaranth, mold spores (especially Alternaria and Aspergillus from agricultural sources), and dust mites. Agricultural dust and fine particulate matter from surrounding farmland compound allergic symptoms.
The San Joaquin Valley is essentially a giant bowl — Sierra Nevada to the east, Coast Ranges to the west, Tehachapi Mountains to the south — that traps pollutants, pollen, agricultural dust, and wildfire smoke. Temperature inversions prevent vertical dispersion. Agriculture, Highway 99 traffic, and industrial operations contribute emissions that cannot escape the basin. The region has been out of EPA compliance for air quality standards for over 25 years.
Yes. HeyAllergy provides telemedicine appointments with board-certified allergists and immunologists licensed in California. Book a virtual consultation from anywhere in the state, have allergy blood tests ordered at a local lab, and start a personalized treatment plan without visiting a clinic. No referral needed and no waitlist.
HeyPak sublingual immunotherapy uses customized liquid drops placed under your tongue daily containing precise doses of the specific allergens triggering your symptoms — whether oak, ryegrass, ragweed, mold, or dust mites. Over time, your immune system builds tolerance, reducing allergic reactions and medication dependence. Most patients notice improvement within 3 to 6 months.
HeyAllergy accepts Medicare and most major PPO health plans, including United Healthcare, Health Net, Anthem Blue Cross, Blue Shield, Cigna, Aetna, Humana, Oscar, and Tricare. Contact your insurance provider with Tax ID: 85-0834175 to confirm your specific telemedicine coverage.
Effectively yes. Tree pollen runs February through May, grass pollen April through July, weed pollen July through November, and agricultural dust peaks during harvest in August through September. Winter brings tule fog trapping pollutants and mold growth. Dust mites and indoor allergens persist year-round. There is no extended symptom-free period in the Central Valley.
Yes. Wildfire smoke contains fine particulate matter that triggers respiratory inflammation independent of pollen allergies. For people with existing allergic sensitization, smoke exposure creates a multiplicative inflammatory response that can cause severe asthma exacerbations. The San Joaquin Valley's bowl geography traps wildfire smoke for extended periods. Treating underlying allergies with immunotherapy reduces overall inflammatory burden and improves resilience during smoke events.
Modesto — population approximately 218,000 and the seat of Stanislaus County — sits at the northern edge of the San Joaquin Valley, one of the most productive agricultural regions on earth. The Central Valley produces roughly 25 percent of America's food on just 1 percent of the nation's farmland, and Stanislaus County ranks among California's top agricultural producers with almonds, walnuts, dairy, poultry, and row crops generating billions in annual revenue. This extraordinary agricultural productivity comes with a significant allergy cost: millions of acres of orchards, fields, and pastures surrounding Modesto produce massive quantities of pollen, agricultural dust, and mold spores that residents breathe year-round. Combined with the San Joaquin Valley's infamous air quality — consistently ranked among the worst in the nation — Modesto presents one of California's most challenging environments for allergy and asthma sufferers.
The San Joaquin Valley is essentially a massive basin — flanked by the Sierra Nevada range (peaks exceeding 14,000 feet) to the east, the Coast Ranges to the west, and the Tehachapi Mountains closing the southern end. The valley opens only to the north through the Sacramento-San Joaquin Delta toward San Francisco Bay. This bowl-like topography has profound consequences for air quality and allergen exposure. Airborne pollutants, pollen, agricultural dust, and wildfire smoke that enter or are generated within the valley have nowhere to go. Temperature inversions — where warm air above seals cooler air near the ground — are common, particularly during winter and late summer, creating stagnant air conditions that concentrate allergens at breathing level. The San Joaquin Valley has been out of compliance with EPA National Ambient Air Quality Standards for both PM2.5 and ozone for over 25 years. Stanislaus County ranks among the state's counties with the highest burden from particulate pollution. For allergy sufferers, this means pollen and particulate matter remain concentrated in the air longer and at higher levels than in regions with better atmospheric dispersion.
Modesto is surrounded by orchards on nearly every side. Stanislaus County is one of California's leading almond-producing counties, and California produces roughly 80 percent of the world's almond supply. Almond trees bloom dramatically in February, producing clouds of white and pink blossoms that attract commercial beekeeping operations from across the country. This early bloom catches many allergy sufferers off guard — pollen season in the Central Valley begins while much of the country is still in winter. Walnut orchards are similarly extensive, pollinating from April through May with wind-dispersed pollen. Beyond orchard pollen, agricultural operations generate massive quantities of airborne dust. Almond harvest in August and September is particularly impactful — mechanical tree shakers and ground sweepers create dust plumes containing fine particulate matter, mold spores from Alternaria and Aspergillus colonizing hulls, and organic debris. This harvest dust has been documented to produce locally elevated PM2.5 concentrations that exceed federal health standards in communities near orchard operations.
Tule fog is a dense radiation fog unique to California's Central Valley, forming when moist air near the ground cools under clear, calm winter conditions, typically from November through February. Named after the tule reeds of the San Joaquin-Sacramento Delta wetlands, tule fog can reduce visibility below 200 feet and persist for days or even weeks under strong temperature inversions. From an allergy and respiratory health perspective, tule fog creates a concentrated layer of trapped pollutants, mold spores, and particulate matter at ground level. During extended fog events, PM2.5 concentrations can spike well above federal standards as emissions from vehicles, agriculture, and industry accumulate in the stagnant air. Mold growth accelerates in the damp conditions, and winter rainfall promotes decomposition of agricultural residue that releases additional mold spores. Many Modesto residents experience their worst respiratory symptoms during prolonged tule fog events, despite low pollen counts, because of this trapped-pollutant concentration effect.
The San Joaquin Valley is acutely vulnerable to wildfire smoke because the same bowl geography that traps local pollutants also funnels and retains smoke from Sierra Nevada and Northern California wildfires. During the catastrophic fire seasons of 2020 and 2021 — when four of the five largest fires in California history burned — Modesto and the surrounding valley experienced weeks of hazardous air quality. Wildfire smoke contains fine particulate matter, volatile organic compounds, and carcinogens that penetrate deep into the lungs, triggering inflammation independent of pollen allergies. For residents with existing allergic sensitization, wildfire smoke creates a multiplicative inflammatory response: the immune system is already primed to overreact to allergens, and the additional inflammatory burden from smoke pushes many patients into severe asthma exacerbations, emergency department visits, and prolonged symptom flares. The Asthma and Allergy Foundation of America consistently ranks San Joaquin Valley cities among the nation's worst "Asthma Capitals" for exactly this combination of allergen exposure and air pollution.
HeyAllergy connects Modesto residents with board-certified allergists and immunologists licensed in California — providing specialist allergy care without the long waits that plague many Central Valley practices. The San Joaquin Valley's high rates of allergic disease create significant demand for allergy specialists, and many residents face months-long waits for in-person appointments. A virtual consultation from your Modesto home eliminates those delays. Allergy blood tests are ordered at a convenient local lab, and a personalized treatment plan is developed based on your specific triggers — whether oak, almond, walnut, ryegrass, ragweed, mold, dust mites, or the complex mix of agricultural allergens unique to the Central Valley. HeyPak sublingual immunotherapy drops ship directly to your door and treat the root cause of allergies by building your immune system's tolerance to your specific triggers. In a region where air quality challenges compound allergen exposure, treating the underlying immune sensitivity is the most effective long-term strategy. HeyAllergy accepts Medicare and most major PPO health plans. Starting at $47 per month, with most patients noticing improvement within 3 to 6 months.
