How to Tell the Difference Between Toxic Black Mold and Mildew

Are you seeing dark spots on your walls, ceilings, or windowsills? I’m not sure if it’s toxic black mold or mildew. Both thrive in damp areas and signal a moisture problem, but they require different solutions.

Ignoring the issue can lead to bigger problems, including health risks and structural damage. The key is knowing what you’re dealing with and how to handle it safely.

In this guide, you’ll learn how to identify black mold vs. mildew, test for growth, and decide when to call a professional.

What Is Mold vs. Mildew?

Mold and mildew are both fungi that thrive in damp areas, but they aren’t the same. Knowing the difference helps you take the right action before the problem spreads.

Mold

Color

Mold appears in black, green, white, or yellow patches. Toxic black mold (Stachybotrys chartarum) is dark green or black and often slimy.

Physical Characteristics

Mold is fuzzy, slimy, has a musty smell, or is thick. It spreads deep into drywall, wood, and insulation, making it harder to remove. It thrives in basements, attics, crawl spaces, and anywhere with high moisture levels. Water damage, HVAC leaks, and humidity speed up its growth.

Mildew

Color

Mildew is usually white, gray, or yellow. Over time, it can turn brown or black.

Physical Characteristics

Mildew growth is flat and powdery. It grows on damp surfaces like bathrooms, windowsills, shower tiles, and fabric. Unlike mold, mildew stays on the surface and doesn’t burrow into materials.

Mildew has a musty smell and can cause minor health issues like runny nose, sneezing, and skin irritation. It’s easier to clean with bleach, exhaust fans, or a dehumidifier. Mildew tends to smell stale, while mold usually smells stronger and earthier.

How to Test for Mold or Mildew 

Mold and mildew don’t always grow in plain sight. Musty odors, water stains, and damp surfaces can signal problems before you see any growth. Testing helps you confirm what’s spreading in your home and how to handle it.

Check for Visible Signs

Start with a visual inspection. Look for black, green, or white patches on drywall, windowsills, basements, attics, and crawl spaces. Mold often hides behind walls or under carpets, especially in damp areas with past water damage.

A musty smell is a red flag. Even if you don’t see mold, lingering odors mean mold spores could be in the air or inside HVAC vents. 

Use a Home Mold Test Kit

A DIY mold inspection kit can detect mold spores in the air or on surfaces. These kits collect samples that you can send to a lab for identification. They won’t tell you the types of mold present but can confirm whether a mold problem exists.

When using a test kit, check multiple areas:

• Basement and crawl spaces (high moisture levels)
• Bathrooms and laundry rooms (damp surfaces, poor ventilation)
• Kitchens and under sinks (hidden leaks)
• HVAC systems and air vents (spore circulation)

If the test is positive, a mold inspection from a professional can determine the affected area and severity of the infestation.

Schedule a Professional Assessment

A certified mold inspector can identify mold types, check for mycotoxins, and measure humidity levels. The EPA recommends professional testing for black mold growth. Mold remediation experts use specialized tools to detect hidden mold inside walls, attics, and crawl spaces.

A professional assessment is necessary if:

• Mold covers more than 10 square feet 
• You have persistent respiratory issues, asthma attacks, or allergic reactions
• There is toxic black mold or extensive water damage
• The mold returns after cleaning

Check for Water Leaks and Humidity Levels

Mold thrives in high humidity and damp conditions. Inspect HVAC systems, exhaust fans, and crawl spaces for trapped moisture. Check for water leaks around windows, ceilings, and pipes. A dehumidifier can help keep moisture levels low and prevent future infestations.

If you find mold, avoid scrubbing it dry, and remember that this does not address the underlying moisture issues. Call a mold removal specialist for larger infestations.

Health Risks and Effects of Mold Exposure

Mold spores travel through the air, triggering allergic reactions, respiratory problems, and long-term health issues. 

Early Symptoms of Mold Exposure

In the early stages, mold exposure may feel like a mild allergy. Common symptoms include:

• Sneezing and runny nose
• Sore throat and coughing
• Itchy eyes and skin irritation
• Musty odor sensitivity

People with mold allergies may react faster. Symptoms often get worse in damp areas like crawl spaces, attics, and bathrooms.

Long-Term Health Effects

Research links black mold exposure to neurological symptoms, lung inflammation, and long-term respiratory damage. Infants, elderly individuals, and people with existing conditions face a higher risk. Mold exacerbates various health problems.

FAQs About Mold Remediation

Can running an air purifier help with mold?

An air purifier with a HEPA filter can trap mold spores, improving air quality, but it won’t stop mold from spreading. To remove mold completely, you need to fix moisture issues and clean affected areas.

Does bleach kill mold?

Bleach is not recommended because it doesn’t kill mold spores deep inside drywall, wood, or insulation. Mold remediation often requires stronger treatments or professional removal of affected home materials.

Can mold spread from one room to another?

Yes. Mold spores travel through the air, spreading through HVAC systems, vents, and clothing. Once mold takes hold in a damp area, it can infest multiple rooms quickly. Stopping mold early prevents larger infestations and expensive cleanups.

When to Seek Professional Help with a Review 

Mold in a rental property can be a legal issue. Landlords are responsible for maintaining safe living conditions under tenant rights laws. You may need legal help if:

• Your landlord ignores written requests for mold removal
• The believe mold is affecting your health or personal property
• You’re facing eviction or rent disputes after reporting mold
• Your landlord is withholding your security deposit due to mold damage

A lawyer can help you understand your lease agreement, state laws, and legal options. In some cases, you may seek compensation for property damage, medical costs, and relocation expenses.

Take Action Before It Gets Worse

Mold doesn’t go away on its own. If your landlord won’t act, or if the problem is beyond DIY fixes, it’s time to get professional help. Schedule a consultation with the Law Office of Paul Mankin to review your options today.