Alder pollen allergy

What it is

Alders (genus Alnus) are relatives of birch. They belong to the birch family, Betulaceae, along with birch, hazel and hornbeam.² That family is part of a wider order of trees, the Fagales, whose pollen is the main cause of winter and spring pollen allergy in the temperate parts of the Northern Hemisphere.²

AAFA lists alder as found in every state except Nebraska and South Dakota.³ In the West, red alder grows along the Pacific Coast from southeast Alaska to southern California. It usually stays within about 100 miles of the coast and below 2,500 feet, with an isolated population in northern Idaho.¹ Before settlement it grew mainly along streams and in wet areas. Logging and other disturbance have since opened bare ground that it colonizes, and red alder stands are now common through much of coastal Oregon and Washington.¹

Red alder carries male and female flowers in separate catkins on the same tree, and it is mainly pollinated by wind. The drooping male catkins can grow to about 5 inches long.¹

Symptoms it causes

Alder pollen is breathed in. AAFA lists alder among the trees that cause the most allergy symptoms in the US.³ 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.⁴

Alder pollen and birch pollen carry related allergens. Alder’s main pollen allergen belongs to the same protein class as birch’s, along with the main allergens of hazel, hornbeam, beech, chestnut and oak, and these related allergens cross-react.²

Alder pollen can also affect what some people eat. In pollen-food allergy syndrome (PFAS), proteins in some tree pollen resemble proteins in certain fruits, vegetables and nuts, so a person allergic to the pollen may react to the food.³ For alder, AAFA names almond, apple, celery, cherry, hazelnut, parsley, peach and pear.³ Eating these foods can make the mouth or face itch or swell, and birch and alder cause the most PFAS food reactions.⁴

Where and when it grows

Alder flowers early. In Oregon and Washington, red alder generally begins flowering in late February and continues until early May. Across its range, timing depends on latitude and climate.¹ The flowers begin to form in spring before the leaves expand.¹

Timing shifts from place to place. At 17 locations in Oregon and Washington, the recorded dates when flowering began ranged from February 19 to May 4.¹

Across the US, trees produce the most pollen from February through April. In some regions, such as the South, trees may release pollen as early as December or January.³