Cottonwood pollen allergy
Populus
Cottonwood pollen flies in early spring and can cause hay fever. The white “cotton” that drifts weeks later is seed fluff, not pollen.
What it is
Cottonwoods are poplars: they belong to the genus Populus.3 AAFA lists aspen and poplar as relatives of cottonwood, and names all three among the trees that cause the most allergy symptoms in the US.7
Eastern cottonwood grows from Alberta to Quebec and south to Florida, Texas and Arizona. Its subspecies include plains cottonwood across the Great Plains and Rio Grande cottonwood along the upper Rio Grande. It is often a dominant tree in floodplain and bottomland forests.5
Eastern cottonwood has separate male and female trees.5 The hanging catkins appear before the leaves.6 In early spring, pollen from the catkins on male trees drifts on the wind to the female flowers.4
Symptoms it causes
Cottonwood pollen is breathed in, and it can cause hay fever symptoms.4 Tree pollen allergy can bring a runny or stuffy nose, sneezing, itchy nose, eyes, ears and mouth, red and watery eyes, and swelling around the eyes. People with allergic asthma may also have asthma symptoms while the trees are releasing pollen.8
Only male trees make pollen. Because of the allergy problems linked to that pollen, male poplars, the group that includes cottonwoods, are banned in some municipalities.3
The white fluff is a different matter. The “cotton” is attached to seeds from female trees and helps them travel far from the parent tree.3 Colorado State University Extension says that although the cotton can be a nuisance, it has no allergenic properties.2 Ohio State University Extension also notes there is no evidence that it triggers allergic reactions.4 CSU Extension adds that people with allergy symptoms while the cotton is flying are probably reacting to other wind-borne pollen, from grasses, weeds or other trees.2
Where and when it grows
Eastern cottonwood flowers in March and April, and its catkins later produce the white, fuzzy seeds called cotton. In Oklahoma it grows throughout the state.1 Colorado State University Extension says the female flowers are pollinated by wind-borne pollen from male trees in April.2 In central New Mexico, the male flowers also release their pollen in April, earlier in the season than the cotton.3
The cotton comes later. CSU Extension says the small green capsules on pollinated female trees split open in June and shed seeds carried by the cotton.2 The seeds mature over the summer.6 A young tree needs several years of growth before it flowers at all.2
AAFA lists cottonwood, aspen and poplar as found in every state except Hawaii.7
The cotton causes problems of its own. It can clog car radiators, swamp coolers and pool filters, and it is very flammable.3
Symptoms it can cause
When to get help
See an allergist if
- Allergy symptoms last for several months of the year
- Allergies bring repeated sinus problems, a blocked nose or trouble breathing
- Over-the-counter remedies don’t control your symptoms
- Allergies or asthma get in the way of daily life
- You often wheeze, cough at night or after exercise, or feel short of breath
Based on ACAAI’s “When To See an Allergist”. General information, not medical advice.
Questions
Is cottonwood fluff an allergen?
No. Colorado State University Extension says the cotton, which carries seeds from female trees, has no allergenic properties. The pollen comes earlier, in April, from male trees.2
Why do my allergies flare when the cotton is flying?
Probably because of other wind-borne pollen, from grasses, weeds or other trees. Colorado State University Extension says the cotton itself has no allergenic properties.2
Which cottonwood trees make pollen?
Male trees. Female trees make the cotton instead. Some municipalities ban male poplars, the group that includes cottonwoods, because of allergy problems linked to their pollen.3
Are aspens and poplars related to cottonwood?
Yes. AAFA describes aspen, cottonwood and poplar as related trees, each found in every state except Hawaii, and lists all three among the trees that cause the most allergy symptoms in the US.7
Sources
- Eastern Cottonwood. Oklahoma State University Extension. Read on October 15, 2026.
- Cottonwood Cotton. Colorado State University Extension, PlantTalk Colorado. Read on October 15, 2026.
- Cottonwood Cotton and Drought-Friendly Flowers. New Mexico State University, Southwest Yard & Garden. Read on October 15, 2026.
- Cottonwoods are Living Up to Their Name in Ohio. Ohio State University Extension, Buckeye Yard and Garden onLine. Read on October 15, 2026.
- Populus deltoides. USDA Forest Service, Fire Effects Information System. Read on October 15, 2026.
- Virginia Tech Dendrology Fact Sheet. Virginia Tech Department of Forest Resources and Environmental Conservation. Read on October 15, 2026.
- Tree Pollen Allergy. Asthma and Allergy Foundation of America. Read on October 15, 2026.
- Tree Pollen: Spring’s First Allergy Offender. Asthma and Allergy Foundation of America. Read on October 15, 2026.