What Allergies Are Bad This Month? Month-by-Month U.S. Pollen Calendar

The Same Month Can Mean Oak in One City and Ragweed in Another

A national pollen calendar is useful only when it is treated as a map—not a stopwatch.

Tree, grass, weed, and mold seasons move across the United States in waves. Latitude, elevation, rainfall, drought, heat, local vegetation, urban planting, and frost dates can shift a peak by weeks. A warm February in Georgia may start tree season while snow still covers parts of Minnesota. September may bring peak ragweed in Ohio while grass remains active in parts of Florida or California.

Quick answer: Trees usually dominate from late winter through spring, grasses from late spring through summer, and ragweed and other weeds from late summer through fall. Winter symptoms often come from indoor allergens, except in mild regions and winter-juniper zones such as Central Texas.

This guide is a living U.S. pollen calendar. It is designed for monthly editorial updates and weekly checks against current weather, local counts, Climate Central seasonal analyses, AAFA reporting, and the AAAAI National Allergy Bureau network.

Clinical review notice: A calendar cannot diagnose your trigger. Symptoms may also come from dust mites, pets, indoor mold, infection, smoke, irritants, or nonallergic rhinitis. Cough, wheeze, chest tightness, and shortness of breath require an asthma-aware plan.

What Allergies Are Bad This Month? August 2026 Snapshot

August is the handoff between summer and fall allergens across much of the country.

The most likely outdoor patterns are:

• Ragweed beginning or rising across the Midwest, Northeast, Plains, Mid-Atlantic, and parts of the South.
• Sagebrush, mugwort, pigweed, amaranth, and Russian thistle becoming important in western and arid regions.
• Grass pollen lingering in northern, high-elevation, coastal, or irrigated areas.
• Outdoor mold spores increasing around warm humidity, crops, compost, cut vegetation, and summer storms.
• Pollen-triggered asthma risk increasing when high allergen levels combine with heat, smoke, ozone, or thunderstorm outflow.

This is a national seasonal baseline—not a statement that every city is high today.

At-a-Glance 12-Month U.S. Pollen Matrix

How to use the matrix

Use the calendar to ask a better question:

Which category should I compare with my local data this week?

Then check:

• Current tree, grass, weed, and mold levels.
• The dominant plant or category.
• Recent rainfall, heat, wind, drought, or frost.
• Whether symptoms followed outdoor or indoor exposure.
• Whether the same pattern repeats each year.

The calendar should narrow your search—not create a blanket avoidance list.

Why the U.S. Allergy Calendar Is Shifting

Longer freeze-free seasons

Climate Central's 2026 analysis examined 198 U.S. cities using NOAA temperature data through 2025.

It found that:

• The freeze-free growing season lengthened in 173 of 198 cities.
• Those cities gained 21 days on average since 1970.
• Every major U.S. climate region showed a longer average growing season.
• The Northwest and Southwest experienced some of the largest regional increases.

A longer time between the final spring freeze and first autumn freeze gives plants more opportunities to leaf, flower, and release pollen.

A freeze-free season is not identical to a measured pollen season. It is a climate indicator that helps explain why historical month labels are becoming less reliable.

Observed pollen trends

A North American study using data from 60 monitoring stations from 1990 through 2018 found:

• Pollen seasons advanced and lengthened by about 20 days across the study period.
• Pollen concentrations increased by about 21%.
• Human-caused climate change was the dominant driver of the timing changes and contributed to increasing concentrations.

These are continental averages. Individual cities, plants, and years can move in different directions.

Higher carbon dioxide can increase pollen production

Plants use carbon dioxide for photosynthesis. Controlled experiments and modeling indicate that higher atmospheric carbon dioxide can increase pollen production for some allergenic plants, particularly grasses and ragweed.

Temperature, moisture, nutrients, species, and land use also matter. It would be inaccurate to attribute every bad week or every city's pollen burden to carbon dioxide alone.

Later frost extends autumn weeds

Ragweed and other annual weeds continue producing pollen until senescence or a killing frost ends the cycle.

A warm autumn can therefore:

• Extend ragweed exposure into October or November.
• Create more overlap with outdoor mold.
• Delay the symptom relief people expect from a historical frost date.
• Increase the number of weeks requiring asthma and rhinitis control.

Severe weather can reshape a season

Rain does not have one universal effect.

It can:

• Temporarily wash pollen from the air.
• Promote plant growth and later pollen production.
• Increase outdoor mold as vegetation decays.
• Delay or compress pollen release.
• Combine with thunderstorm outflow to create short-lived lower-airway hazards.

The Thunderstorm Asthma and Pollen Guide explains why a storm can briefly worsen breathing risk even when steady rain usually lowers pollen.

Geography Matters More Than a National Ranking

AAFA's Allergy Capitals report is valuable, but it is often misread.

The 2026 report ranked Boise, Idaho, first among the 100 largest contiguous-U.S. metropolitan areas. The ranking combined:

• Tree pollen scores.
• Grass pollen scores.
• Weed pollen scores.
• Over-the-counter allergy medicine use.
• Availability of board-certified allergists and immunologists.

A city's rank is therefore not a pure pollen-count leaderboard, and it does not predict which month will be worst for a specific person.

The 2026 list also demonstrated that severe seasonal burden is not confined to one region. Western, Southern, Midwestern, Northeastern, and coastal cities appeared near the top.

A useful interpretation is:

Local climate, vegetation, health-care access, medication burden, and year-to-year weather can make almost any region challenging for the right sensitization.

January: Winter Cedar and Indoor Exposure

January is not an allergy-free month.

Outdoor triggers

In Central Texas, Ashe juniper—commonly called mountain cedar—often creates a major winter pollen event. Texas A&M Forest Service describes a season that typically begins in mid-December, peaks around mid-January, and tapers toward early March.

Other possible January pollens include:

• Juniper and cedar in parts of the South and Southwest.
• Cypress in mild climates.
• Early alder or hazel in selected West Coast locations.
• Early trees after an unusually warm southern winter.

Indoor triggers

Cold-weather behavior raises exposure to:

• Dust mites in bedding and upholstered furniture.
• Pet allergens.
• Indoor mold around condensation or leaks.
• Cockroach and rodent particles.
• Smoke, fragrance, and combustion irritants.

Winter congestion should not automatically be blamed on pollen. Infection and dry heated air can produce overlapping symptoms.

February: Early Trees Move North

Tree season often expands during February.

Likely triggers

• Alder and hazel in parts of the Pacific Northwest and West Coast.
• Juniper and cedar in the South and Southwest.
• Elm, maple, cypress, and other early trees in warmer eastern regions.
• Continuing mountain cedar in Central Texas.

Weather signal

Several warm days after winter chill can accelerate bud development. A cold snap may pause release without resetting the entire season.

Someone who historically started medication in March may need an earlier plan after repeated warm winters. Use local counts rather than the old calendar date alone.

March: Tree Pollen Accelerates

March often marks a sharp expansion of spring tree pollen.

Common regional contributors

• Oak.
• Elm.
• Maple and box elder.
• Ash.
• Juniper and cypress.
• Alder.
• Poplar and cottonwood.
• Mulberry in some southern and western areas.

Regional pattern

The South and lower Mid-Atlantic may already be heavily active. The lower Midwest begins rising, while colder northern regions may still be early in the cycle.

Dry, warm, windy conditions can create abrupt count spikes. Rain may offer brief relief without ending the season.

April: The Broad Tree-Pollen Wave

April is one of the most difficult months for tree-sensitive people across large parts of the United States.

Frequent culprits

• Oak.
• Birch.
• Maple.
• Hickory.
• Ash.
• Sycamore.
• Poplar.
• Beech.
• Willow.

The yellow-dust problem

Visible yellow dust is often produced by pine or other conspicuous pollens. A visible coating does not prove that the most abundant dust is the allergen causing your symptoms. Less visible oak, birch, grass, or other pollen may be more clinically important.

The Tree vs. Grass vs. Weed Pollen Guide helps separate timing, plant groups, symptoms, and cross-reactions.

May: Tree and Grass Overlap

May often creates a double exposure: late tree pollen plus accelerating grass.

Common grass groups

• Timothy.
• Orchard grass.
• Ryegrass.
• Fescue.
• Kentucky bluegrass.
• Sweet vernal.
• Bermuda grass in warmer regions.

Why symptoms can suddenly change

A person allergic only to trees may begin improving while a grass-sensitive person becomes worse. Someone sensitized to both can experience one long continuous season.

Lawn mowing, sports fields, parks, and dry windy days can create concentrated personal exposure even when a regional index is moderate.

June: Grass Becomes the Main Story

June is a common grass-pollen peak in northern, central, and many temperate regions.

Higher-exposure activities

• Mowing.
• Field sports.
• Golf.
• Hiking through meadows.
• Hay handling.
• Outdoor events on grass.
• Driving or sleeping with windows open.

Warm-season grasses may dominate farther south, while cool-season grasses are more important in northern climates.

Use the Lawn Mowing and Yard Work Allergy Checklist before high-exposure chores.

July: Grass, Mold, and Early Weeds

July is not the same everywhere.

In northern or high-elevation regions

Grass may remain the leading trigger.

In warm, humid regions

Outdoor mold often becomes increasingly important. Spores can rise around:

• Crops.
• Compost.
• Cut grass.
• Soil.
• Decaying leaves or wood.
• Humid nights and warm days.

Early weed transition

Ragweed and other weeds may begin producing measurable pollen late in the month, especially after heat or drought stress.

The Mold Allergy Guide explains how outdoor spore exposure differs from indoor moisture-driven growth.

August: Ragweed Season Builds

August begins the main fall-pollen transition across much of the country.

Eastern and central regions

Ragweed becomes increasingly important, especially across:

• The Midwest.
• Northeast.
• Mid-Atlantic.
• Great Plains.
• Parts of the South.

Western and arid regions

Important weeds may include:

• Sagebrush.
• Mugwort.
• Pigweed or amaranth.
• Russian thistle.
• Tumbleweed.
• Lamb's-quarters.

Symptoms to track

Ragweed can cause:

• Sneezing.
• Watery nasal drainage.
• Itchy eyes.
• Nasal congestion.
• Asthma symptoms.
• Pollen-food reactions to selected raw foods in sensitized people.

September: The Classic Ragweed Peak

In many regions, ragweed pollen is highest in early to mid-September.

That does not mean September is universally worst. Western weeds, warm-season grass, drought, smoke, and mold may create a different local pattern.

Factors that extend or intensify September symptoms

• Warm nights.
• Delayed frost.
• Dry windy weather.
• Disturbed vacant lots and roadsides.
• Agricultural activity.
• Smoke or ozone irritating pollen-sensitive airways.

Prepare with the Ragweed Allergy Guide, which covers season timing, symptom patterns, treatment, and pollen-food cross-reactions.

October: Frost Determines the Finish Line

October can bring relief in a northern city and ongoing weed exposure in a southern one.

Before the first killing frost

Ragweed and other weeds may continue releasing pollen.

After frost

Outdoor pollen often falls, but symptoms can continue because of:

• Outdoor mold around fallen leaves.
• Pollen carried indoors on clothing and pets.
• Indoor dust mites or pet allergens.
• Ongoing inflammation after the exposure falls.
• Warmer pockets within a region.

Do not stop a prescribed seasonal plan solely because the calendar changed. Follow symptom, count, and clinician guidance.

November: Outdoor-to-Indoor Transition

In colder regions, November shifts attention indoors.

Common indoor problems

• Dust mites in bedding.
• Pet allergens accumulating with closed windows.
• Mold around condensation.
• Dirty humidifiers.
• Heating-system dust and irritants.
• Cockroach or rodent particles.

A furnace does not create pet allergy or dust mite allergy, but turning on forced air can redistribute settled particles if filters, ducts, or housekeeping are poor.

The Dust Mite Allergy Guide covers encasements, laundry, humidity, and bedroom source control.

December: Mountain Cedar Returns

Mountain cedar or Ashe juniper becomes a defining outdoor trigger in Central Texas and can affect surrounding areas through wind transport.

Typical Texas pattern

• Starts around mid-December.
• Often intensifies after dry cold fronts.
• Peaks around mid-January.
• Tapers toward early March.

Nationwide pattern

Elsewhere, winter symptoms more often reflect indoor exposure, respiratory infections, dry air, or irritants. Mild southern and coastal regions can still have outdoor pollen.

Regional Allergy Calendars

Northeast

A classic pattern is:

1. Early trees in March.
2. Broad tree peak in April or May.
3. Grass from May into July.
4. Ragweed from August until frost.
5. Outdoor mold around summer humidity and autumn leaves.

Warm coastal areas can start earlier than inland or northern locations.

Midwest and Ohio Valley

Common waves include:

• Maple, elm, oak, and other trees in spring.
• Grass in late spring and early summer.
• Ragweed and mixed weeds in late summer and fall.
• Strong outdoor mold around crops, soil, and decaying vegetation.

Agricultural activity and regional winds can create exposures not obvious from a city landscape.

Southeast and Gulf Coast

The season is longer and overlaps more heavily.

Possible patterns include:

• Tree pollen beginning in winter or very early spring.
• Oak and pine-related visible dust in spring.
• Bermuda and other grasses active for extended periods.
• Ragweed and weeds in late summer and fall.
• Outdoor mold through long warm, humid periods.

A single “spring allergy” label may miss year-round or multiple sensitizations.

South-Central and Texas

Distinctive features include:

• Mountain cedar from December into February or early March.
• Oak and other trees in spring.
• Bermuda and other grasses through warm months.
• Ragweed and weeds in late summer and fall.
• Mold and agricultural exposures.

A person can move from cedar directly into oak and grass with little symptom-free interval.

Southwest and Desert Regions

Common triggers can include:

• Juniper and cedar.
• Mulberry and olive where planted.
• Mesquite.
• Ash.
• Bermuda grass in irrigated landscapes.
• Sagebrush.
• Pigweed and amaranth.
• Russian thistle.

Desert does not mean pollen-free. Irrigation and urban planting create concentrated local sources.

Mountain West and High Elevations

Elevation compresses and delays seasons.

A valley can begin tree pollen weeks before a mountain town. Grass may remain active later in cool locations, while sagebrush and other weeds dominate late summer and fall.

Rapid weather shifts and wildfire smoke can complicate symptom interpretation.

Pacific Northwest

Possible patterns include:

• Alder and hazel in late winter.
• Birch, maple, cedar, and other trees in spring.
• Grass in late spring and summer.
• Outdoor mold during damp or decaying-vegetation periods.

The region's long moisture season makes it important to distinguish outdoor spores from indoor building dampness.

California and the Pacific Coast

California contains multiple pollen climates.

Coastal, inland-valley, desert, and mountain calendars differ. Depending on location, important sources may include:

• Alder.
• Cypress.
• Oak.
• Olive.
• Mulberry.
• Grasses.
• Sagebrush and weeds.
• Year-round outdoor mold in selected coastal environments.

Local city data is substantially more useful than a statewide month label.

Alaska and Hawaii

These states are not represented in AAFA's contiguous-U.S. Allergy Capitals ranking.

Alaska has a short but potentially intense tree and grass season that varies with latitude and spring thaw.

Hawaii's tropical climate can support long or year-round exposure to grasses, molds, and locally important plants. The continental winter-spring-summer-fall framework fits poorly there.

How to Track Your Personal Allergy Calendar

1. Use counts and forecasts for different jobs

A pollen count measures particles collected at a station and identified after sampling.

A pollen forecast predicts what may happen using weather, historical data, vegetation, and models.

Counts are observations but may be delayed and far from your neighborhood. Forecasts are timely but uncertain.

The best strategy is to compare both with symptoms. The How to Read a Pollen Forecast Guide explains the difference in detail.

2. Track categories before individual species

Record:

• Tree score.
• Grass score.
• Weed score.
• Mold or spore information when available.
• Dominant allergen.
• Weather.
• Outdoor duration.
• Symptoms.
• Medication use.

After several weeks, the pattern may show that “spring allergy” is specifically tree-related or that a supposed ragweed problem follows outdoor mold instead.

3. Use a simple daily score

Rate each item from 0 to 3:

Add location and exposure notes. A symptom score is more useful when it can be compared with the same category each day.

4. Prepare before the expected rise

Many allergy medicines work better when used consistently before inflammation becomes severe.

The correct lead time depends on:

• The medication class.
• Product label.
• Prior seasonal pattern.
• Age.
• Pregnancy or health conditions.
• Clinician instructions.

Intranasal corticosteroids generally require consistent use for several days and sometimes longer for full benefit. Grass and ragweed immunotherapy tablets have product-specific preseason schedules measured in months—not a generic two-week start.

Use the Allergy Medicine Guide to match treatment class to symptom and onset.

5. Confirm the trigger when the calendar is not enough

Consider an allergist when:

• Symptoms overlap several seasons.
• Indoor and outdoor triggers are unclear.
• Medication is needed for many months.
• Cough or wheeze occurs.
• Symptoms disrupt sleep or work.
• Immunotherapy is being considered.
• The expected pollen category does not match the symptom pattern.

Skin prick and specific IgE blood tests show sensitization and must be interpreted with exposure history. They should not be used as stand-alone diagnoses.

The Allergy Testing Guide explains how focused testing avoids unnecessary broad panels.

Weather Events That Break the Calendar

An unusually warm winter

Can bring early tree flowering and a longer overlap with later species.

A late freeze

Can delay, reduce, or damage flowering for some plants while leaving others less affected.

A rainy spring

Can promote vegetation growth and later pollen, while temporarily lowering airborne counts on rainy days.

Drought

Can suppress some plants but favor drought-tolerant weeds, dust, smoke, and highly variable pollen release.

Wind

Can move pollen from distant sources and create a high-exposure day before local plants appear active.

Wildfire smoke

Does not increase pollen by itself, but fine particles and gases can irritate airways already inflamed by allergy.

Thunderstorms

Can lower pollen after sustained rain but create dangerous short-term outflow conditions for selected pollen-sensitive people with asthma.

First frost

Often ends ragweed and many annual weed seasons, but the timing and temperature required vary by plant and region.

Common Calendar Mistakes

Treating national months as local facts

The calendar is a baseline. A city-level count should override it.

Assuming visible yellow dust identifies the culprit

Conspicuous pollen is not always the most allergenic or clinically relevant pollen in the air.

Calling every winter symptom “indoor allergy”

Mountain cedar and early trees are major exceptions, and infection remains common.

Assuming green means grass

Map colors, index colors, and pollen categories differ among providers. Read the legend.

Starting medicine only after the peak

A reactive plan allows inflammation to build before treatment is consistent.

Stopping at the first rainy day

Rain changes short-term exposure; it does not end the plant's season.

Using the AAFA ranking as a personal diagnosis

The report compares metro-level burden using several factors. It does not reveal your sensitization.

When the Symptoms Are More Than Hay Fever

Pollen can trigger lower-airway inflammation and asthma.

Seek prompt assessment for:

• Cough during pollen exposure.
• Wheezing.
• Chest tightness.
• Shortness of breath.
• Night waking.
• Reduced exercise tolerance.
• Frequent prescribed reliever use.
• Falling peak-flow readings.

Call 911 for severe or rapidly worsening breathing, inability to speak normally, blue or gray lips, confusion, fainting, marked retractions, or poor response to prescribed rescue treatment.

The Practical Bottom Line

A U.S. pollen calendar works best as a layered system:

1. Use the month to identify the most likely allergen group.
2. Adjust for region, altitude, and climate.
3. Check current local counts and forecasts.
4. Compare conditions with your symptom diary.
5. start treatment according to the product and clinical plan—not a generic date.
6. Reassess when the season moves earlier, lasts longer, or no longer matches history.

The modern allergy season is less predictable than the calendar many people grew up with. That makes local data and a personal pattern more valuable, not less.

For persistent, overlapping, or asthma-associated symptoms, find a local allergist in the AllergyAva directory for a diagnosis-driven seasonal plan.