Yes, May is one of the most intense months of allergy season across most of the United States. It sits at a unique overlap point where late-season tree pollen hasn’t fully cleared and grass pollen is ramping up, meaning you can be hit by two major allergen categories at once. For many people, May represents the peak of spring allergy symptoms.
Why May Is a Double-Hit Month
Tree pollen dominates from roughly February through April across most of the U.S., but several species extend well into May. Oak trees, one of the most potent triggers, can pollinate into May depending on your region. Juniper, cedar, and cypress trees release pollen from January all the way through May and sometimes into June. Pine trees produce the visible yellow dust that coats cars from February through May, though pine pollen is actually less allergenic than what you can’t see.
At the same time, grass pollen season runs from April through early June. So in May, the tail end of tree pollen overlaps with the front end of grass pollen. This overlap is what makes May particularly rough. If you’re sensitive to both, your body is processing a wider variety of allergens than it would in March (mostly trees) or July (mostly weeds).
What Counts as a High Pollen Day
Pollen is measured in grains per cubic meter of air. For tree pollen, anything above 90 grains per cubic meter is considered high, and counts above 1,500 are classified as very high. Grass pollen triggers symptoms at lower concentrations: above 20 grains per cubic meter is high, and above 200 is very high. In May, it’s common for both tree and grass counts to land in the moderate-to-high range on the same day, which is why symptoms can feel more persistent than earlier in spring.
Your local pollen count matters more than national averages. Pollen.com and local allergy clinics post daily counts that break down tree, grass, and weed levels separately. Checking these can help you plan outdoor activities on lower-count days.
When Pollen Peaks During the Day
Contrary to the old advice about avoiding early mornings, research shows pollen concentrations are actually lowest between 4 a.m. and noon. Levels climb gradually through the afternoon and peak between 2 p.m. and 9 p.m. If you want to exercise outside or open windows, morning is your best window.
Weather plays a major role too. Warm, dry, windy days carry the highest pollen loads because there’s no moisture to weigh pollen down, so it stays airborne longer and travels farther. Thunderstorms are a special case: they stir up pollen and can break grains into smaller particles that penetrate deeper into the lungs, sometimes triggering severe symptoms even in people whose allergies are usually mild.
The Season Is Getting Longer
If May allergies feel worse than they did a decade ago, you’re not imagining it. Pollen season in the U.S. is approximately three weeks longer now than it was 50 years ago, according to the American Lung Association. Warmer temperatures cause plants to start producing pollen earlier and continue later, which stretches May’s overlap window and increases the total amount of pollen released over the season.
Indoor Allergens Rise in May Too
Pollen isn’t the only concern. As humidity climbs in late spring, indoor allergens like dust mites and mold become more active. Dust mite populations thrive when indoor relative humidity exceeds about 69%, and mold can begin growing on surfaces in rooms with poor ventilation. If your symptoms persist even when you stay indoors with windows closed, rising humidity may be compounding the problem. Running a dehumidifier to keep indoor humidity below 50% helps suppress both dust mites and mold growth.
Starting Treatment Before May
Nasal steroid sprays work best when they’ve had time to reduce inflammation before heavy pollen exposure begins. The general recommendation is to start allergy medications about two weeks before your local season kicks in. If May is your worst month, that means beginning treatment in mid-April. Antihistamine pills work faster and can be started on the day symptoms appear, but nasal sprays need that lead time to reach full effectiveness.
For people whose symptoms span multiple pollen seasons, starting as early as February makes more sense, since tree pollen is already active by then in most regions. The key is knowing which specific pollens trigger your symptoms. An allergist can test for sensitivities to individual tree and grass species, which tells you exactly when your personal allergy season starts and ends rather than relying on general calendars.
Practical Ways to Reduce May Exposure
- Time outdoor activities for mornings when pollen counts are at their daily low, ideally before noon.
- Shower and change clothes after being outside to remove pollen from your hair and skin before it spreads to furniture and bedding.
- Keep windows closed on windy days and use air conditioning with a clean filter instead of relying on outdoor air.
- Dry laundry indoors since hanging clothes outside lets pollen settle into fabric.
- Watch for thunderstorms as a signal to stay inside, since storm winds can break pollen into smaller, more irritating particles.
If you’ve only ever associated allergies with early spring, May deserves just as much attention. The tree-grass overlap, rising humidity, and lengthening pollen seasons all converge to make it one of the most challenging months for anyone with respiratory allergies.