Mulberry pollen allergy

What it is

Mulberries are trees in the genus Morus, and two species grow widely in the US. White mulberry is native to China and was brought to North America in the 1600s. In 1624, Virginia required its male residents to plant the trees to promote a silk industry.¹ White mulberry now grows across the whole country except Nevada and Alaska, and many cultivated varieties exist.¹

Red mulberry is native. Its range runs from Massachusetts and southern Vermont west to southeastern Minnesota and south to central Texas and southern Florida. It usually grows as scattered trees in floodplain or cove forests, and it hybridizes with white mulberry.²

White mulberry trees are generally either male or female, with male and female flowers in separate catkins, and the species is pollinated by wind.¹ In Yavapai County, Arizona, white mulberry was commonly planted for its dense shade and heat tolerance. Male trees, known as “fruitless mulberry,” were once favored because they avoid the messy fruit of female trees. They make no fruit but plenty of pollen.⁴

Symptoms it causes

Mulberry pollen is breathed in. In patients in Spain, exposure to white mulberry pollen has been reported to cause asthma, allergic rhinitis (hay fever) and allergic conjunctivitis, which affects the eyes.³ The first report, from 1971, described the effect of mulberry trees on respiratory allergy in Southern California. Mulberry pollen has since drawn attention in the US, Spain and Asia because of the many cases of rhinitis or asthma.³

AAFA lists mulberry among the trees that cause the most allergy symptoms in the US and describes it as very allergenic.⁶ In Yavapai County, Arizona, some regard fruitless mulberry as a significant source of allergy, and people with allergies there now see it as more trouble than it is worth.⁴ University of Arizona Cooperative Extension also notes that bringing exotic species into local landscapes can make the allergen problem worse, and that this has led some communities to ban planting olive and mulberry trees.⁵

Paper mulberry is a separate tree. Its scientific name is Broussonetia papyrifera, it belongs to a different genus in the same plant family, and it is native to Asia. In Pakistan, its pollen is a major cause of respiratory allergy.³

Where and when it grows

White mulberry generally flowers from April to May. It starts as early as March in the Carolinas and can keep flowering into June in the upper Midwest.¹ Red mulberry catkins appear in April and May.²

Local timing can differ. In Yavapai County, Arizona, the University of Arizona Cooperative Extension lists the fruitless mulberry pollen season as February to March.⁴

White mulberry also spreads on its own into disturbed ground, such as roadsides, vacant lots, pastures, fields and fencerows.¹