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Fungi

Penicillium

Common name: Penicillium mold

Neutral to harmful Respiratory Respiratory tract Sinuses Other
Neutral to harmful
Effect
Respiratory
Impact
Respiratory tract, Sinuses, Other
Location
Very Common
Prevalence
Last reviewed: September 23, 2026

Large genus of molds that decompose organic matter, spoil food, and produce mycotoxins; some species are common indoor allergens, and one is the historic source of penicillin

Prevalence: Found worldwide on decaying organic material, on food, and in indoor air; Penicillium chrysogenum is one of the two most common molds in water-damaged buildings

Interacts with: Aspergillus, Cladosporium, Alternaria, Stachybotrys chartarum, Immune system

Overview

Penicillium is one of the most important mold genera in everyday life. Its species are found worldwide and play major roles as decomposers of organic material. They also cause destructive rots in the food industry, where they produce a wide range of mycotoxins. Other species serve as industrial "enzyme factories," and some are common indoor air allergens.[1]

Indoors, Penicillium chrysogenum is, together with Aspergillus versicolor, one of the two most common fungi on materials in water-damaged buildings.[2] And the genus holds a unique place in medical history: a Penicillium strain gave the world penicillin.[3]

Classification

  • Phylum: Ascomycota
  • Family: Aspergillaceae
  • Genus: Penicillium
  • Accepted species: 354 (as of 2014)

Penicillium is a large and diverse genus, with 354 accepted species in a 2014 revision. DNA sequencing is essential for robust species identification.[1] The genus boundaries have also shifted. In 2011, species in the former Penicillium subgenus Biverticillium were transferred to a separate genus, Talaromyces. This included medically important species such as the fungus formerly called Penicillium marneffei, now Talaromyces marneffei.[4]

Fleming's mold, renamed

The mold that Alexander Fleming observed producing penicillin was long attributed to Penicillium notatum or P. chrysogenum. Genetic analysis in 2011 showed that the most important penicillin-producing isolates fall into two species, and that Fleming's original strain is actually Penicillium rubens. The two species look alike but differ in the compounds they produce.[3]

Where Penicillium Is Found

  • Food. Penicillium species are a major cause of food spoilage and can produce mycotoxins as they grow.[1] Certain species are also used intentionally to ripen blue and soft-rind cheeses.
  • Indoors. P. chrysogenum is a commonly occurring indoor mold.[3] In a study of more than 5,300 samples from moldy building materials, it was associated with gypsum board and wallpaper, together with Acremonium, Stachybotrys, and Ulocladium.[2]
  • Outdoors. Penicillium species occur worldwide as decomposers of organic material.[1]

Health Significance

Allergy and asthma

Some Penicillium species are common indoor allergens.[1] A review of the evidence found a close association between fungal sensitization and asthma severity, involving several airborne fungi including Penicillium, Aspergillus, Alternaria, and Cladosporium. Exposure can be indoors, outdoors, or both. Whether this association is causal has not been confirmed.[5]

Mycotoxins in food

Because Penicillium species produce a wide range of mycotoxins during food spoilage,[1] visible mold on food should be taken seriously. Discard moldy soft foods, bread, and leftovers, since mold can spread below the visible surface, and follow food safety guidance for firmer foods.

Infection

Invasive infections caused by true Penicillium species are rarely reported. Some of the best-known "Penicillium" infections are caused by fungi now classified in Talaromyces, such as Talaromyces marneffei.[4] When Penicillium grows in a clinical sample, clinicians consider whether it represents true infection or contamination from spores in the air.

Reducing Indoor Penicillium

  1. Control moisture. Fix leaks promptly and keep indoor humidity moderate. Visible Penicillium growth indicates a moisture problem.
  2. Remove damaged materials. Moldy gypsum board and wallpaper usually need removal rather than surface cleaning.
  3. Store food properly and discard moldy soft foods.
  4. Ask about testing if you have asthma or allergies that worsen indoors. Our allergies and hay fever protocol covers research on the microbiome's role in allergic disease.

Other molds often found alongside Penicillium in damp buildings include Stachybotrys chartarum, Chaetomium, Cladosporium, and Aspergillus niger. For more on building-related mold, see our guide to warning signs of mold toxicity.

When to See a Clinician

See a clinician if you have wheezing, persistent cough, sinus symptoms, or allergy symptoms that worsen at home or in damp buildings. People with weakened immune systems should seek care promptly for new respiratory symptoms or fever.

This page is for educational purposes and is not medical advice. Consult a qualified healthcare provider about mold exposure, allergies, and asthma.

Associated Conditions

→ Asthma → Allergies → Allergic Rhinitis

Related Organisms

A
Alternaria Respiratory
A
Aspergillus fumigatus Respiratory
A
Aspergillus niger Respiratory
B
Bordetella pertussis Respiratory
B
Burkholderia cepacia complex Respiratory
C
Chaetomium Respiratory

Frequently Asked Questions

Is Penicillium mold harmful?

For most healthy people, brief exposure to Penicillium is not harmful; its spores are common in indoor and outdoor air. It matters most for people with mold allergy or asthma, since some Penicillium species are common indoor allergens and fungal sensitization is associated with more severe asthma. Some species also produce mycotoxins on spoiled food, which is why visibly moldy food should be discarded.

Is Penicillium mold the same as penicillin?

No. Penicillin is an antibiotic molecule that certain Penicillium strains produce. Alexander Fleming's original penicillin-producing mold, long called Penicillium chrysogenum or P. notatum, was re-identified in 2011 as Penicillium rubens. A penicillin drug allergy is a reaction to the antibiotic, which is different from an allergy to mold spores; ask your clinician if you are unsure about either.

What does Penicillium in my house mean?

Penicillium spores are common indoors, but visible growth usually means excess moisture. Penicillium chrysogenum is one of the two most common molds found on materials in water-damaged buildings, and it is associated with gypsum board and wallpaper. The key step is finding and fixing the moisture source.

Is the mold in blue cheese Penicillium?

Yes. Certain Penicillium species are deliberately used to ripen blue and soft-rind cheeses, and these food cultures are considered safe to eat. That is different from unintended mold growing on food, which can include toxin-producing species.

Research References

  1. Visagie C, Houbraken J, Frisvad J, et al.. Identification and nomenclature of the genus Penicillium. Studies in Mycology. 2014. doi:10.1016/j.simyco.2014.09.001 ↩
  2. Andersen B, Frisvad JC, Søndergaard I, Rasmussen IS, Larsen LS. Associations between Fungal Species and Water-Damaged Building Materials. Applied and Environmental Microbiology. 2011. doi:10.1128/aem.02513-10 ↩
  3. Houbraken J, Frisvad JC, Samson RA. Fleming’s penicillin producing strain is not Penicillium chrysogenum but P. rubens. IMA Fungus. 2011. doi:10.5598/imafungus.2011.02.01.12 ↩
  4. Samson R, Yilmaz N, Houbraken J, et al.. Phylogeny and nomenclature of the genus Talaromyces and taxa accommodated in Penicillium subgenus Biverticillium. Studies in Mycology. 2011. doi:10.3114/sim.2011.70.04 ↩
  5. Denning DW, O'Driscoll BR, Hogaboam CM, Bowyer P, Niven RM. The link between fungi and severe asthma: a summary of the evidence. European Respiratory Journal. 2006. doi:10.1183/09031936.06.00074705 ↩