Mold vs Mildew: Understanding the Difference

In any home, in dark and damp spaces such as basements and bathrooms, you might discover some unwelcome guests, namely mold or mildew. But when it comes to showing either of them the door, you first need to know what you’re dealing with.

So what are mold and mildew? Theresa Schnorbach, sleep scientist from Emma, explains: “While mildew and mold may differ in appearance and preference for where they grow, both are types of fungus, which release spores that could pose a health risk.”

Not only can mold and mildew cause health issues, their presence can affect your sleep as well as cause damage to your home. Getting an air-quality monitor can help you identify whether mold is the root cause of any breathing problems, however it’s always best to tackle the mold directly.

In this guide, we reveal everything you need to know about both mold and mildew, as well as the tools to obliterate both.

How do you identify mold and mildew?

Mold and mildew are types of fungi. Mildew refers to specific types of fungus, which includes some types of molds. You might sometimes hear mildew used as a generic term to refer to mold that has a flat growth. Mold includes all species of microscopic fungi – these grow in the form of multicellular filaments called hyphae.

“It’s important to note that mildew is not a separate entity from mold, but rather a variety of it,” explains Michael Rubino, a mold and air quality expert, environmental wellness advocate, and founder of HomeCleanse. “The term ‘mildew’ describes mold growth that’s light in color and powdery in texture. These mold colonies, often gray, white, or light green, grow in a flat format without much height, distinguishing them from other types of mold.”

Tony Abate, certified mold inspector, vice president, and chief technology officer at AtmosAir Solutions, explains further: “Mildew is gray, white, or light brown in color and generally lies flat on the surface of a moist area. It has a powdery appearance that may have a distinct, foul odor. Mold has a fuzzy, raised appearance and in unaired areas has a strong, musty smell. It often appears in darker shades of black, green, and red.”

Mold is often raised and can have a fuzzy, slimy, or furry feel to it. It’s particularly common in bathrooms, around windows, and on skirting boards, and can have a strong, earthy odor.

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What causes mold and mildew?

Both mold and mildew are caused by damp, moisture, excess humidity, poor ventilation, and a lack of natural light (which is the reason it’s so common to find them in bathrooms). Mold and mildew spores land on a surface, germinate, and then grow, with growth starting as soon as 24-48 hours after a surface has been dampened.

The speed at which mold or mildew grows is determined by a room’s relative humidity, so you can stop the problem in its tracks by preventing this excess moisture. Note, too, that mildew spots spread outwards, not upwards, whereas mold eats inwards, making it more difficult to remove.

The most common places to find mold and mildew are:

• Around showers and bathtubs
• In or around areas where water is dripping (drainpipes and gutters, for example)
• Under carpeting
• In crawl spaces
• In ceilings, near exhaust fans or recessed lights
• Near HVAC or clothes dryer vents

Mold and mildew health concerns

Human and pet health can be affected by mold and mildew in the home, with mold the cause of more serious issues. “Although mildew can cause minor respiratory problems such as coughing fits, it isn’t as invasive or troublesome as mold”, says Tony Abate. “Molds can cause many health problems ranging from irritations and allergic symptoms to hypersensitivity and respiratory issues from prolonged exposure to mold”, he adds.

Michael Rubino expands further: “As mildew and mold grow, they release spores, fragments, and other particles into the surrounding environment. These particles are small enough to be inhaled into the body; some are so small that they can bypass the lungs and go straight into the bloodstream. The longer the growth is present, the more exposure you’ll face.”

This is a problem for a few reasons. Over time, exposure to this volume of particles can lead to a toxic buildup in the body and trigger a long list of potential adverse health reactions. Also, as the number of spores inside a home continue to grow, so too do the chances of other mold and mildew colonies developing elsewhere, adding another source of indoor air contamination, according to Rubino.

Spores and fragments aren’t the only sources of indoor air contamination, however. As Rubino explains: “Quite a few species of fungi – such as Aspergillus, a “common mold”, according to the CDC – fall under the mildew umbrella. This particular species of mold can create toxic byproducts called mycotoxins, which is the reason mildew is no less of a home health threat than other varieties of mold. Both mold and mildew should be treated in the same way: quickly and correctly.”

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Mold and mildew problems overnight

Problems caused by mold and mildew can be particularly prevalent at night, explains Theresa Schnorbach. “Mold and mildew growth in the bedroom can compromise air quality; breathing in these pollutants can cause headaches, dizziness, and fatigue. Moreover, inhaling spores during sleep can lead to respiratory problems such as coughing, wheezing, shortness of breath, and chest tightness. These irritating and uncomfortable symptoms often interfere with the ease with which you fall asleep, as well as your capacity to stay asleep once you do drift off.”

For individuals with asthma or allergies, exposure to mold or mildew can worsen symptoms and make it more difficult to breathe comfortably during the night. “This can be exacerbated by allergies to mold,” Schnorbach adds. “An allergic reaction can trigger symptoms such as a runny nose, itchy throat, and sore eyes, which can all make it difficult to sleep. Allergy-induced sleep deprivation can lead to a buildup of sleep debt, which can have a big impact on your health – both physical and mental,” she explains.

Anxiety and stress associated with the presence of mold and mildew can also have a psychological effect on our ability to rest. “This psychological distress can interfere with relaxation and make it harder to fall and stay asleep. In particular, tension and nervousness can impact the REM phase of sleep, which may worsen one’s stress management, which in turn can further aggravate feelings of anxiety,” adds Schnorbach.

How to prevent mold and mildew

There are plenty of steps you can take to prevent mold and mildew from ever becoming a problem. These include:

• Keep everything clean – Don’t allow dirt and debris to build up, since this will provide a fertile breeding ground for the fungi.

• Increase ventilation – As we’ve already discussed, mold and mildew will be particularly prevalent in damp areas. Extractor fans in the bathroom, and an extractor hood above your cooker will help to dry out these rooms and add ventilation.

• Use natural ventilation – Air out rooms regularly, ensuring windows remain open (if possible).

• Use dehumidifiers – If you have damp rooms that won’t dry out even with airing, consider investing in dehumidifiers to reduce humidity.

• Check mechanical vents – If you have mechanical venting such as HVAC vents, make sure they remain open and unblocked.

• Inspect vents for clothes dryers – Make sure that these vents are kept clean and that they’re firmly attached.

• Check for underlying problems – If you’re still experiencing problems with mold and mildew, you may have an underlying damp problem. Check for leaking pipes and guttering, but do call in a professional if no immediate cause can be found.

Tony Abate adds: “Keeping your home dry is key to avoiding mildew and mold. Be sure to avoid water leaks; ensure basements are sealed. Landscaping should be sloped away from the home, so water doesn’t collect around the foundations. Rain gutters should be in good working condition. If there is a spill or leak, clean then dry it and surrounding surfaces quickly. Be sure air ducts are cleaned regularly.

“Lastly, the heating and air conditioning (HVAC) system in your home can also harbor mold, so ensure it’s properly serviced. Regular care and maintenance is important to avoid any buildup, to keep critical components clean, and provide a healthy environment for your family and loved ones. In addition, upgrading and enhancing the air quality in your home with an indoor air purification system – bi-polar air ionization, for example – installed in your HVAC system will remediate microbial growth, help deter mildew and mold, and improve the overall air quality in your home.”

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How to treat mold and mildew

Michael Rubino offers this comprehensive advice for dealing with mold and mildew. “Since mold and mildew are similar, they should be treated equally when removing the contamination. The key is to follow the correct procedures,” he explains.

“Successful remediation involves addressing the source that allowed the mold to develop, removing the active growth, and eliminating all associated contamination. Proper remediation means all contamination must be eradicated, including the colony, roots, dead mold particles, mycotoxins, and any bacteria. If this is not done, the microbial growth may persist, and the area will still be contaminated with harmful microscopic particles.”

Small projects

If you’re undertaking a small project of less than 10×10 feet, it’s perfectly feasible to manage this yourself. The first step is to identify whether you’re working with a non-porous, semi-porous, or porous surface, as the approach will be different for each.

• Non-porous: “For non-porous surfaces like sealed countertops, apply a botanical cleaner, let it sit for 30 seconds, then wipe it with a microfiber towel,” explains Michael Rubino. “Microfiber towels are 100 times more effective than regular rags at removing tiny particles. Repeat this process at least two more times to ensure all contaminants, including mycotoxins, are removed. Use a clean side of the cloth every time.”

• Semi-porous: “For semi-porous surfaces, mold roots (called hyphae) can penetrate the material, making it difficult to remove completely,” says Michael Rubino. “All particles and the root system must be removed to ensure the surface is contaminant-free. Think of it like removing a weed. Use the same technique as non-porous surfaces and seal the surface if possible. For hardwood, abrasive methodologies like sanding should be completed to remove the roots before sealing. Hydrogen peroxide can help lift particles to the surface for easier removal of grout or caulk. Monitor the surface to ensure the mold does not return quickly, indicating a deeper issue that may require professional help or replacement of the surface.”

• Porous: “Remove and replace the material for porous surfaces like drywall, clothing, or fabric furniture,” explains Michael Rubino. “The contamination can exist deep within the fibers and be impossible to remove altogether. Discarding and replacing porous surfaces/items like clothing is also best. If you want to attempt to remediate this surface, use a HEPA vacuum cleaner thoroughly on the surface and throw it in the wash with a botanical laundry additive. This will not guarantee the mold or mildew is completely gone, though.”

Large projects

Larger projects are best left to professionals, as Michael Rubino explains: “For larger projects, the first step is to call a qualified mold inspector to assess the status of your home. This person should spend hours inside your house, going through it with a fine-tooth comb and conducting various tests to determine if there are any issues, hidden or visible, existing inside. This data will give the remediation team the necessary information to eliminate all the contamination present. For all projects, use engineering controls, personal protective equipment (PPE), and proper remediation protocols to avoid inhaling aerosolized particles and prevent cross-contamination. Additionally, deep clean the surrounding area to remove any particles released during the process. It is best to contact a professional if unsure about handling the situation.”