Penicillium Chrysogenum: Indoor Mold, Health and Cleanup

We may earn commission from links on this page. Lead-form submissions are forwarded to local inspector partners. How we research and review.

Penicillium chrysogenum has an unusual double reputation. In medicine it is famous as the mold behind industrial penicillin production. In buildings it is one of the more common molds found growing on damp drywall, wallpaper, carpet, dust and stored food. A homeowner may run across the name on a lab report, in an inspection summary, or after searching for a blue-green spot on a wall. This guide explains what the species is, how it is related to the mold Alexander Fleming studied, what it usually looks like, where it grows indoors, what it may mean for health, how labs report it alongside Aspergillus, and how to clean it up and keep it from returning.

Part of our Types of Mold guide — start there for the full picture →

What Is Penicillium Chrysogenum?

Penicillium is a large genus of fungi with hundreds of described species. They are found in soil, on decaying plants, on food and in indoor environments around the world. Penicillium chrysogenum is one of the species most often associated with indoor growth. The CDC lists Penicillium, together with Cladosporium and Aspergillus, as the most common indoor molds, and P. chrysogenum is among the Penicillium species frequently reported from damp buildings in the scientific literature.

Like other molds, it grows as a network of fine threads called hyphae and reproduces by releasing enormous numbers of tiny spores. Under a microscope, Penicillium spores are borne in chains on brush-like structures; the genus name comes from the Latin word for a painter’s brush. Those spores are small and light enough to stay airborne and to travel through a home on air currents, on clothing and through HVAC systems.

The species name chrysogenum roughly means “producing gold,” a reference to the yellow pigment that many strains release into the material they grow on. For a broader introduction to the genus, see our guides on what Penicillium is and Penicillium mold. For other species pages, browse our mold types hub.

The Penicillin Connection

The story most people know is that Alexander Fleming noticed in 1928 that a mold contaminating one of his bacterial culture plates seemed to stop bacteria growing around it. That observation led, over the following years and through the work of many other researchers, to penicillin as a medicine.

The naming history is more tangled than the popular story, and it is worth treating with some care. Fleming’s mold was long identified as Penicillium notatum. Later taxonomic work grouped P. notatum with P. chrysogenum, and more recent genetic studies are generally understood to place Fleming’s original isolate in a closely related species, Penicillium rubens, within what is often described as the P. chrysogenum species complex. Different sources use these names in slightly different ways, so it is common to see Fleming’s mold called P. notatum, P. chrysogenum or P. rubens depending on when and where the account was written. Our guide to Penicillium notatum covers that older name.

The strains used for large-scale penicillin manufacturing are widely described as descending from a high-yield isolate found during wartime research in the 1940s, then improved over decades of selection. Whatever the exact naming, the practical point for homeowners is simple: the medicine and the mold on a damp wall are related, but finding P. chrysogenum in a house has nothing to do with antibiotics. Growing on drywall, it is just another indoor mold that signals a moisture problem.

What Penicillium Chrysogenum Looks Like

On building materials, most Penicillium species, including P. chrysogenum, tend to look broadly similar. Typical descriptions include:

• Color: blue-green to green on the surface, often with a white outer edge where the colony is still growing. Older areas may look greyish-green.
• Texture: velvety to powdery, sometimes with a slightly fuzzy look.
• Reverse and pigment: in laboratory culture, the underside of the colony is commonly described as yellow, and the mold may release yellow pigment and small yellowish droplets on its surface.
• Pattern: round spots that merge into larger patches as growth spreads.

These features are typical, not guaranteed. Colony appearance depends on the material, moisture, temperature and age of the growth, and many other molds are also blue-green. A homeowner cannot reliably tell P. chrysogenum from other Penicillium species, or from Aspergillus, by eye. Species-level identification requires culture and microscopic or genetic analysis in a lab. Our guide to Penicillium under the microscope shows what lab analysts look for.

How It Compares to Other Penicillium Species and Aspergillus

The table below compares P. chrysogenum with two well-known food Penicillium species and with Aspergillus, the genus it is most often grouped with on lab reports. Descriptions are general and simplified.

Where Penicillium Chrysogenum Grows Indoors

Penicillium species are able to grow on many common materials once moisture is present. The EPA’s Brief Guide to mold explains that mold spores are usually not a problem indoors unless they land on a wet or damp spot and begin growing, and that the way to control mold growth is to control moisture. P. chrysogenum fits that pattern. Common places include:

• Water-damaged drywall and wallpaper: the paper facing of drywall is an easy food source after a leak or flood.
• Carpet and carpet pad: especially after spills, pet accidents, flooding or chronic basement dampness.
• Behind furniture against exterior walls: where cool walls and poor air movement allow condensation.
• Window frames and sills: where condensation collects in winter.
• HVAC components: damp drip pans, dirty coils, and dust in ductwork near moisture sources.
• Attics and crawl spaces: on wood, insulation facing and stored cardboard when ventilation or drainage is poor.
• Food: fruit, bread, cheese and other stored food, where blue-green Penicillium spots are a familiar sight.

Many Penicillium species can grow on materials that are damp rather than soaked, and some tolerate cool temperatures, which is why they often show up in basements and on cold exterior walls. Our guide to Penicillium mold in the house covers room-by-room hot spots.

Why Penicillium spreads so readily indoors

Several traits help explain why Penicillium species, P. chrysogenum among them, are so often found in homes. Each colony produces very large numbers of small, dry spores that are easily lifted into the air when a surface is disturbed, whether by cleaning, foot traffic or an air register blowing across it. Many species tolerate cool temperatures and grow on materials that are only intermittently damp, such as a wall that collects condensation on winter nights and dries during the day. And the genus is not fussy about food: paper, dust, glue, fabric and organic residues all serve. In the EPA’s framing, spores are always present and the deciding factor is moisture, so a home that stays dry gives P. chrysogenum little opportunity, while one with a slow leak or chronic condensation gives it plenty.

The EPA advises that if you suspect an HVAC system is contaminated with mold, for example because it is part of an identified moisture problem or there is mold near the intake, you should consult its guidance on duct cleaning before taking further action. Running a contaminated system can spread spores through a home.

Signs of Penicillium Growth in a Home

Because P. chrysogenum is rarely named on a basic report, most homeowners encounter it as “some blue-green mold” first. Signs that Penicillium-type growth may be present include:

• Blue-green or green velvety spots on drywall, wallpaper, window frames, the back of furniture or stored items.
• A musty, earthy odor in a closet, basement or room that has had a leak, even when no growth is visible.
• Yellowish staining around or beneath patches, which can come from pigment released by some strains.
• Recurring growth on the same cold wall, window or bathroom ceiling each winter.
• Allergy-type symptoms that seem worse in one part of the house, which is a reason to look for moisture, not proof of mold.

The CDC’s guidance is that if you see or smell mold, you should remove it, and that you do not need to know the type of mold to do so. Finding the moisture source matters more than confirming the species. Hidden growth commonly sits behind baseboards, under sinks, inside wall cavities after plumbing leaks and under carpet near exterior doors.

Health Effects: What Is Known

For most people, P. chrysogenum is mainly a potential allergen, not an infection risk. The evidence on health effects comes largely from studies of damp, moldy buildings in general rather than from this species alone, so the discussion below is about molds broadly, including Penicillium.

Allergy and asthma

The EPA’s Brief Guide explains that molds produce allergens, irritants and, in some cases, potentially toxic substances called mycotoxins. It notes that allergic reactions to mold are common, that they can be immediate or delayed, and that molds can cause asthma attacks in people with asthma who are allergic to mold. Mold exposure can also irritate the eyes, skin, nose, throat and lungs of both allergic and non-allergic people.

The CDC similarly notes that damp and moldy environments may cause a variety of health effects, or none at all. For some people, mold can cause a stuffy nose, sore throat, coughing or wheezing, burning eyes or skin rash, and people with asthma or mold allergies may have severe reactions. Penicillium is a recognized allergen group, and some people are specifically sensitized to it. Our guide to Penicillium allergy covers symptoms and how sensitization is usually assessed by a doctor.

Infection risk

Penicillium chrysogenum is not generally regarded as a common cause of infection in healthy people. The CDC notes more broadly that people with weakened immune systems and people with chronic lung disease may get infections in their lungs from mold. Anyone in those groups who is living with mold growth should talk with a doctor, and should avoid doing cleanup themselves.

Penicillin allergy is a different issue

A common worry is whether someone allergic to penicillin should be concerned about Penicillium mold. A drug allergy to penicillin and an allergy to mold spores are generally understood to be different immune responses to different substances. Anyone with a known drug allergy who has questions about mold exposure should ask their doctor rather than assume either way. For a fuller look at the risks, see is Penicillium mold dangerous.

This article is general information, not medical advice.

How Labs Report It: “Penicillium/Aspergillus-Like”

Many people searching for P. chrysogenum have seen it, or its genus, on an air-sample report. Here is what that usually means.

Spore trap reports group the two genera

The most common indoor air test is a spore trap, which captures airborne particles on a sticky slide that is then examined under a microscope. Penicillium and Aspergillus spores are small, round and very similar in appearance under routine microscopy, so labs commonly report them together as “Penicillium/Aspergillus,” “Pen/Asp” or “Penicillium/Aspergillus-like.” A spore trap report almost never names P. chrysogenum specifically. Our guide to Aspergillus/Penicillium on lab reports explains this category in depth.

Culture or DNA methods are needed for species

To name P. chrysogenum, a lab generally has to grow the sample in culture or use DNA-based methods. That level of detail is rarely needed to make cleanup decisions in a home.

What the EPA and CDC say about testing

The EPA’s guidance on mold testing states that in most cases, if visible mold growth is present, sampling is unnecessary. It also notes that no EPA or other federal limits have been set for mold or mold spores, and that sampling should be conducted by professionals with specific experience in designing sampling protocols and interpreting results. The CDC, for its part, does not recommend routine mold testing and advises that whatever type of mold is present, it should be removed.

Testing can still be useful in some situations, such as when there is a musty odor with no visible source, after remediation to check that an area was cleaned adequately, or for real estate and health-related decisions. When it is done, results are usually interpreted by comparing indoor samples to an outdoor sample taken at the same time. Our guide to air sampling for mold explains how that comparison works. Homeowners who want a starting point sometimes use a mold test kit, keeping in mind the limits the EPA describes.

Cleaning Up Penicillium Chrysogenum

You do not need to know the species to clean up mold. The approach is the same for P. chrysogenum as for any common indoor mold, and it follows the EPA’s Brief Guide.

1. Fix the moisture first. Repair leaks, address condensation and dry wet materials. Cleaning without fixing the water source means the mold will return.
2. Size up the job. The EPA suggests that if the moldy area is less than about 10 square feet, in most cases you can handle the cleanup yourself. Larger areas, extensive water damage, contaminated HVAC systems or sewage-related water call for professional help.
3. Protect yourself. Wear gloves, goggles and, for anything beyond a small patch, an N-95 respirator as the EPA describes, and avoid stirring up spores.
4. Scrub hard surfaces. The EPA advises scrubbing mold off hard surfaces with detergent and water, then drying completely.
5. Remove porous materials. Absorbent or porous materials such as ceiling tiles and carpet may have to be thrown away if they become moldy, because mold can fill in their crevices and be difficult or impossible to remove completely.
6. Do not just paint over it. The EPA advises not to paint or caulk moldy surfaces; clean and dry them first.

Bleach is not a shortcut. The EPA notes that dead mold may still cause allergic reactions in some people, so it is not enough to simply kill mold; it must also be removed. Never mix chlorine bleach with cleaners containing ammonia.

When to bring in a professional

Professional help makes sense when growth covers more than about 10 square feet, when the water damage came from sewage or contaminated water, when the HVAC system may be involved, when mold keeps returning after cleaning, or when someone in the home has asthma, a weakened immune system or a chronic lung condition. The EPA advises that anyone hiring a contractor should check references and make sure the contractor has experience cleaning up mold. A home inspector can help locate moisture sources such as roof leaks, plumbing leaks, grading problems and condensation points, which is the part of the job that keeps Penicillium from coming back. The EPA also advises consulting a health professional before starting cleanup if you have health concerns.

Preventing Penicillium Growth

Because P. chrysogenum spores are a normal part of indoor and outdoor air, prevention is about moisture, not about eliminating spores. Steps drawn from EPA and CDC guidance include:

• Keep indoor relative humidity below 60 percent, ideally between 30 and 50 percent, as the EPA recommends.
• Fix leaks in roofs, plumbing and windows promptly, and dry wet materials within 24 to 48 hours.
• Use bathroom and kitchen exhaust fans vented to the outdoors, and vent clothes dryers outside.
• Keep HVAC drip pans clean and drain lines flowing.
• Improve air movement behind furniture on exterior walls and in closets.
• Discard moldy food promptly and keep the refrigerator clean, since food is a common Penicillium source.

On the Colorado Front Range, low outdoor humidity helps, but over-humidifying in winter, finished basements with poor drainage, and swamp coolers can all create indoor dampness. For a broader view of how inspectors find and assess mold, visit our mold inspection section.

References

• About Mold — Centers for Disease Control and Prevention
• A Brief Guide to Mold, Moisture and Your Home — U.S. Environmental Protection Agency
• Mold Testing or Sampling — U.S. Environmental Protection Agency

Got a lab report flagging Penicillium/Aspergillus and not sure what to do next? Talk to our team about tracking down the moisture behind it.

DIY mold test kits

A test kit can confirm whether a suspect patch is mold and (with lab analysis) what type — though visible mold over ~10 sq ft generally warrants a professional.

Product	Why	Buy
DIY Mold Test (lab included)	Surface + air-sampling options.	Amazon — $26.09
Healthful Home 5-Minute Mold Test	Rapid screening strips.	Amazon — $35.47
Mold Test Plates (DIY petri dishes)	Settle-plate style sampling you culture at home.	Amazon — $22.99

Compare more picks in our full buying guide →

Prices and availability are accurate as of October 14, 2026 and are subject to change. Product data via the Amazon Product Advertising API.

We may earn commission from links on this page. Lead-form submissions are forwarded to local inspector partners. How we research and review.