Alternaria mold allergy

What it is

Alternaria is a mold, a kind of fungus. One species, Alternaria alternata, is one of the most common fungi in the air, both outdoors and indoors.⁴ It lives in soil and on plants and is usually thought of as an outdoor allergen, though it also gets into homes.⁵ Like other molds, it spreads by releasing spores that float in the air, much like pollen.²

Of the hundreds of kinds of mold, only some cause allergy. The AAAAI names Alternaria among the most common allergy-causing molds, along with Aspergillus, Cladosporium and Penicillium.¹ A 2025 review that ranks airborne spores by how strongly they provoke allergy puts Alternaria probably at the high end of the scale.⁶

Symptoms it causes

Alternaria causes symptoms when its spores are breathed in. Mold allergy can bring sneezing, a runny or stuffy nose, itchy, watery eyes and an itchy nose, mouth and lips.¹ It can also set off asthma symptoms such as wheezing, shortness of breath and chest tightness.¹ The AAAAI notes that mold allergy is not usually a cause of long-lasting symptoms such as headache and fatigue.¹

Alternaria stands out among molds for its link with asthma. Sensitivity to it has been tied to asthma that starts or persists, to more severe asthma, and to flare-ups that lead to hospital and intensive care admissions in children and adults.⁴ In a study of 914 children with asthma in Connecticut, 6% had a positive Alternaria skin test, and those children were more likely to have severe persistent asthma.⁴

The link shows up outdoors and indoors. A review of outdoor mold studies found that asthma flare-ups in children were associated with Alternaria and Cladosporium spores in the air.³ In a survey of 831 US homes, people living with higher levels of Alternaria in their house dust were more likely to have active asthma symptoms.⁵

Where it’s found

Alternaria exposure is heaviest outdoors in the summer and fall months, when spore levels in the air peak.⁵ Levels run especially high in late summer and after thunderstorms and high winds.⁴ In children, a positive Alternaria skin test is very common in warm, dry climates such as Arizona’s and much less common in cool, wet coastal areas.⁴

Across the US, outdoor mold spores start to climb as temperatures rise in spring. They peak around July in warmer states and around October in colder ones, and in the South and on the West Coast they can be found all year.² National Allergy Bureau stations measure mold levels in the air, and the AAAAI suggests staying indoors when mold counts are high and avoiding mowing or raking leaves, which stirs molds up.²

Alternaria also gets indoors. In the national survey, it was detected in 95 to 99% of house dust samples, depending on where in the home the dust was collected.⁵ Mold grows indoors wherever there is moisture, such as around leaks in roofs, windows or pipes, or after a flood.⁷ The CDC advises keeping home humidity no higher than 50% all day and fixing leaks in the roof, walls or plumbing.⁷ The EPA suggests keeping indoor humidity between 30% and 50%, running an exhaust fan or opening a window when showering or cooking, and drying damp items within one to two days.⁸