Cladosporium mold allergy

What it is

Cladosporium is a mold, a kind of fungus, and one of the most plentiful in the air. A research summary published by the AAAAI calls it the most frequent mold in temperate countries.³ In a study of more than 12,000 air samples from 1,717 buildings across the US, Cladosporium was among the most common molds grown from both indoor and outdoor air, across seasons and regions.⁴

Molds spread by releasing spores that float in the air, much like pollen.² Of the hundreds of kinds of mold, only some cause allergy. Cladosporium is one of the most common that do, along with Alternaria, Aspergillus and Penicillium.¹

Symptoms it causes

Cladosporium 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 trigger asthma symptoms such as wheezing, shortness of breath and chest tightness.¹ The CDC adds that some people sensitive to mold get itchy or red eyes and skin irritation, and that people with asthma or mold allergy may have severe reactions.⁶

Spore for spore, Cladosporium seems to be a weaker allergen than Alternaria. A 2025 review puts it probably at the low end of the scale of allergy-provoking spores, while noting that no airborne spores are entirely harmless.⁵ Its sheer numbers still matter. In a Danish study of asthma hospital admissions, the link with Cladosporium began once levels passed about 1,200 spores per cubic meter of air.⁵ Cladosporium and Alternaria levels tend to rise together and may act jointly in sensitive people.⁵

A review of outdoor mold studies found that asthma flare-ups in children were associated with both Cladosporium and Alternaria spores.³ The evidence for adults is more limited and less consistent.³

Where it’s found

Outdoors, Cladosporium spores are typical of dry weather. A 2025 review calls Cladosporium perhaps the best example of the spores seen in the air during dry spells.⁵ In most temperate areas, outdoor fungal spore levels are low in the cold months, rise through spring and summer, and peak in late summer or early fall as dead and dying plant matter builds up.⁵

In the US, outdoor mold spores peak around July in warmer states and around October in colder ones, and they can be found all year in the South and on the West Coast.² The national air study found the highest mold levels in summer and fall and in the Southwest, Far West and Southeast.⁴ The AAAAI suggests staying indoors when mold counts are high and avoiding mowing or raking leaves, which stirs molds up.²

Indoors, Cladosporium is one of the three most common molds, with Penicillium and Aspergillus.⁶ In the national study, mold levels in indoor air were lower than in outdoor air.⁴ Mold grows indoors where there is moisture, such as around leaks in roofs, windows or pipes, or after a flood, and it can grow on paper, cardboard, ceiling tiles and wood.⁶ To limit it, the CDC advises keeping home humidity no higher than 50% all day, fixing leaks in the roof, walls or plumbing, using kitchen and bathroom exhaust fans that vent outside, and removing mold you can see or smell.⁶