Penicillium Mold in Homes: Risks, Prevention & Removal Tips
You've probably seen the fuzzy blue-green mold on bread, fruit, and even old books. That is Penicillium, one of the most prevalent molds found in houses, food, and structures. While it is well recognized for producing penicillin, not all strains are "helpful." Some can cause food deterioration, allergies, and even health problems if left unchecked in indoor situations.
For homeowners, the catch is that Penicillium mold doesn't necessarily look like it's a threat. It tends to hide behind walls, underneath cabinets, or in wet corners, where it spreads unnoticed. Most people think of it as harmless, but exposure over time can lead to respiratory problems, allergic reactions, and exacerbate conditions such as asthma.
Here in this blog, we will dissect what homeowners need to know about Penicillium mold—where it develops, how to identify it, when it is a threat, and most importantly, the mold remediation process. If you know these steps, you can protect your home and your family's health.
What is Penicillium?
Penicillium is a fungus with more than 300 species. Most of them are blue, green, or yellow spored and soft, powdery, or velvety in texture. The name of the genus is derived from the Latin word for "paintbrush," penicillus, because the spore-producing structures resemble a brush when viewed through a microscope.
Some Penicillium species are very valuable: Penicillium chrysogenum (formerly P. notatum) is where penicillin, the antibiotic, comes from. Some are utilized for the production of some cheeses (consider Camembert or Roquefort). But when Penicillium appears in your house—on food, drywall, or insulation—it's no longer beneficial; it means there is moisture and possible issues.
Where Is Penicillium Mold Found in California Homes?
In our experience conducting home inspections in and around Orange County, we have found Penicillium mold in some unexpected areas. Let us summarize based on thousands of actual inspections:
The Usual Suspects
Storage areas for food are ground zero for Penicillium development. We've discovered it on everything from fruit and bread to coffee beans and wine bottles. That overwhelming musty, earthy odor that's more pungent than most other molds? That's usually your first indicator that Penicillium has taken up residence.
Wood buildings are a favorite, too. Basement rafters, ceiling joists, and even hardwood floors can support Penicillium, particularly in homes with small moisture problems that homeowners are not yet aware of.
Books and paper products provide ideal settings for this fungus to grow. We've had cases where entire home libraries were victimized by Penicillium growth, especially those with low ventilation.
The Hidden Locations
It is within HVAC systems that we have some of the most problematic Penicillium growth. Once this mold has set up house within your duct system, it will distribute spores throughout your entire home with each run of the system.
Behind wallcovering and beneath carpeting are typical hideaways, particularly in older California homes where small plumbing leaks might have been overlooked.
Penicillium may grow on upholstered furniture, especially items kept in basements or garages where there are changing moisture levels.
Is Penicillium Mold Dangerous?
The short, practical answer: usually not for most healthy people, but it can be a problem.
Mild–Moderate Risks
Most Penicillium species are allergenic. That means they can trigger:
Sneezing, runny nose, itchy or watery eyes
Coughing or wheeze in people with asthma
Skin irritation if you handle moldy items
If you or a family member already has allergies or asthma, even “common” Penicillium can make symptoms worse.
More Serious Risks
Several Penicillium species form mycotoxins—chemicals that have more severe effects with greater exposures or ingestion (rare in household situations). These include:
Ochratoxin A (produced by some species) - associated with kidney injury and potential carcinogenicity when exposed to high levels over many years.
Penitrem A (by some like P. crustosum) - neurotoxicity that's worst if ingested (pets have been poisoned by moldy food).
Furthermore, immunocompromised individuals may become infected with fungal species that healthy immune systems easily overwhelm.
“Is Penicillium Aspergillus Dangerous?” — Clearing Up the Confusion
They aren't. Penicillium and Aspergillus are two distinct genera of mold. Both occur indoors, and both contain species that produce mycotoxins or infect susceptible individuals.
Aspergillus includes species like A. fumigatus that are a known risk for lung infections in immunocompromised people.
Penicillium includes species that produce penicillin, cheese-making strains, but also species that produce toxins like ochratoxin.
So, both groups contain species harmless to most individuals and potentially hazardous species. The proper thing is to treat any unexplained mold growth with seriousness and deal with the sources of moisture.
What Does Penicillin Mold Grow On? The Science Behind Growth Patterns
The species Penicillium has been employed traditionally for the production of penicillin. In laboratory or manufacturing environments, such species were cultivated on nutrient media under controlled conditions. In domestic environments, analogous Penicillium species develop naturally on:
Spoiled food (fruit, bread) — sugar and starches are ideal for many Penicillium species.
Damp cellulose materials — paper, cardboard, wallpaper, drywall paper faces.
Wood and insulation — if the material retains moisture.
So while penicillin manufacture is a laboratory operation, the group of molds to which that species belongs flourishes on common organic materials when there is moisture.
The California Climate Factor
California's varied microclimates pose special challenges to controlling Penicillium. We have our coastal regions with fluctuating humidity that can initiate growth cycles, and our interior regions that frequently enjoy ideal moderate temperatures that Penicillium loves.
Homes constructed before 1980 have been found to have more instances of Penicillium, partly because they were not constructed with the same emphasis on moisture control and ventilation as are contemporary building codes.
Health & Safety: When to Worry and When to Act
Here’s a homeowner-friendly checklist:
Take action quickly if:
Mold affects greater than approximately 10 square feet (EPA cut-off for DIY vs. pro).
You can't find or stop the source of moisture.
Members of your household consistently experience allergy symptoms, worsening asthma, or suppression of immunity.
Mold in HVAC systems, within walls, or beneath flooring (hidden mold).
Small patches (smaller than ~3×3 ft) on closed, non-porous surfaces often can be removed by homeowners using safety measures—gloves, goggles, and an N95 respirator. Porous substances (insulation, ceiling tiles, carpet) typically require removal.
How to Remove and Prevent Penicillium in Your Home
We recommend a two-pronged approach: kill/remove the mold, and fix the moisture that allowed it to grow.
Basic cleanup for small areas
Protect yourself: N95 mask, gloves, and eye protection.
Ventilate the area—open windows and run an exhaust fan if possible.
Scrub non-porous surfaces with detergent and water, or an EPA-registered antimicrobial if you prefer.
Dry thoroughly—use fans and dehumidifiers. Mold returns if it stays damp.
Discard porous items (wet carpet padding, soaked books) that can’t be fully cleaned.
Preventive steps
Keep indoor relative humidity under 50% (ideal 30–50%).
Fix any leaks within 24–48 hours (mold can begin colonizing quickly).
Use exhaust fans in bathrooms/kitchens and vent them outdoors.
Clean and inspect HVAC drip pans, ducts, and filters regularly.
Store food properly and discard spoiled items promptly.
When to call a pro
Infestation is large (>10 sq ft).
Mold is inside the HVAC, behind walls, or you suspect hidden contamination.
Family members are ill or immunocompromised.
You want lab confirmation of species or spore counts for health or insurance reasons.
A professional examination will employ moisture meters, borescopes, and (if necessary) air and surface testing to establish scope and source. Proper remediation involves containment, HEPA filtration, removal of materials that have been damaged, and ensuring that moisture issues are resolved.
Protect Your Home with Mold Detection SoCal
Penicillium mold is beneficial in nature and even in medicine, but within your home, it's a sign of trouble. Water issues, secret leaks, or improper ventilation can all welcome Penicillium to move in, and though not all strains are highly poisonous, any mold within your home will cause allergic reactions, respiratory issues, or worse if left alone.
The secret to safeguarding your loved ones is prompt action—repairing leaks, lowering humidity, and safely cleaning small spots before they become large areas. But for massive growth, concealed infestation, or chronic health issues, it's best to have a professional inspection so you understand what you're up against.
If you live in Orange County, Los Angeles, Riverside, or San Diego and fear your home has Penicillium mold, Mold Detection SoCal can help. Call (949) 254-0884 for skilled mold testing, clear findings, and advice on the best next actions to safeguard your home and health.