Molds come in all shapes, sizes, and colors, and while some may think that color can serve as an identifying characteristic, unfortunately, it is not. The main means of identifying molds involve looking closely at the structure, spore, and growth morphology, which isn’t easily done without access to a lab. Color isn’t a good distinguishing characteristic of mold or toxicity because one patch can have multiple colors or change color for several reasons. Some factors that affect mold color are:
- Food source
- Humidity level
- Light exposure
Regardless of what color a mold is, if it’s in your house, that’s a sign that there is an active moisture problem and it should be removed as soon as possible so the moisture problem can be fixed. Here’s a guide to mold colors that you might find in your home.
Green is the most common color for mold. There are hundreds of thousands of types of mold and thousands of them appear as green at some point during their life. So when it comes to green mold, the color won’t tell you much, but chances are that it’s one of these three:
Black mold is an infamous member of the mold family, but not all black molds are the toxic black mold. While it’s important to deal with all molds as soon as possible, dealing with toxic black mold should be handled by a professional. There are several different kinds of black mold that can be commonly found in a house, so watching out for certain characteristics can give you an idea of how urgent its removal is.
Stachybotrys chartarum is the infamous toxic black mold. It often appears as black or greenish-black in color and can be found growing in leaky areas, old decaying wood, paper, and foods. S. chartarum requires constant moisture to maintain growth, so the quicker these areas are addressed, the less of a threat it will be. You may find black mold inhabiting your basement after a flood or around a roof leak. The reason S. chartarum is so dangerous is that it produces a fungal by-product called a mycotoxin, which can be ejected into the air and inhaled by humans and animals. Studies show that exposure to indoor toxic mold like S. chartarum accounts for far more deaths in the U.S. than previously thought. Exposure to mycotoxins like those found in S. chartarum can result in headaches, sneezing, coughing, rashes, and sometimes even blood poisoning.
It’s crucial to be aware of the possibility that a black-colored mold could be S. chartarum, but there’s a good chance that it’s Alternaria, which is much less dangerous. Alternaria species usually grow outdoors in dusty, damp areas near plants and soil, although recently they have been found growing in houses. Exposure to Alternaria could exacerbate asthma, but other than that, it doesn’t pose many health risks.
Aspergillus is another common fungus that studies suggest you actually breathe in every day. Exposure in large amounts can result in aspergillosis and other respiratory problems in those who have pre-existing conditions.
Black-colored mold in the home can also be a species of Cladosporium mold, which usually grows outdoors on decomposing leaves. It can find its way indoors and colonize walls, insulation, and carpet, and exposure can sometimes lead to skin rashes, eye irritation, and sinus infections.
Purple is not a common color for mold to be, but if you do see it, it’s probably a color variant of toxic black mold—Stachybotrys chartarum.
White is another common color for mold growing in the home and it can be one of a few different types.
There’s a good chance that any white mold found in your home is Alternaria. This is one example where one mold can change color depending on conditions.
Chaetomium is a mold that can thrive anywhere—it’s adaptable and resilient. It can grow on many hosts regardless of what they’re made of, but it prefers damp, dark locations. Some might describe it as cotton-like in appearance, and others may write it off as salt deposits on basement walls. One of the distinguishing characteristics of Chaetomium is its scent; it is often the culprit of the musty odor that you may smell in basements, attics, and on foods.
Penicillium is another multi-color fungus that can sometimes be white. The discovery of the Penicillium genus served as a monumental step in the medical field as it led to the creation of Penicillin. It can be found on food and walls in homes with high humidity and while it is an important ingredient in Penicillin, it can cause serious allergic reactions if improperly handled.
Blue is another common color to see in Penicillium molds found on food and walls.
You might find a discolored, pink film on your shower curtain or bathtub if they have gone unwashed for a while—this is known as “pink mold.” Calling it a mold, though, is a misnomer because it’s actually a bacterium called Serratia marcescens that thrives on soap residues. There’s no permanent solution except to clean your bathroom more regularly, but while it can cause urinary tract infections and respiratory problems, luckily it’s not easy to get infected.
Yellow is a color to look out for because some of these molds can be dangerous if left unchecked.
Sometimes Aspergillus mold can appear yellow. As mentioned before, in the black mold section, it’s a very common type of mold found in houses and is largely low-risk.
Serpula lacrymans isn’t dangerous for humans as much as it is for the structural integrity of wooden structures. This fungus is an excellent destroyer of damp and rotting organic material, which can spell disaster for your house if not removed. It grows quickly and consumes indoor and outdoor wooden surfaces with ease if the conditions are ideal.
Epicoccum nigrum is a fast-growing, yellow mold that can be found in or on damp drywall, mattresses, wood, carpets, and furniture. It ranges in color from yellow to orange to brown depending on conditions and surroundings.
Geomyces pannorum is a more unique fungus than the others on this list—it only grows in cooler conditions. This means that it is largely relegated to damp walls, floors, wood, and paper in northern hemisphere climates.
Yellow Slime Mold
If you come across a slimy, bright yellow mold in your home, stay very far away from it. Don’t touch it or inhale it as best you can. Bright yellow molds are usually not true molds, rather they’re an unrelated organism called a “slime mold.” Slime molds can be very toxic and exposure should not be taken lightly. None of the other yellow molds in this list are bright yellow—they’re more of a whitish or brownish-yellow—so a yellow slime mold should be easy to distinguish.
You may spot red mold on building materials such as particleboards or drywall that have been subjected to water damage. Red is usually not a consistent color for mold to be, and it usually will change colors over time. Many species of mold can become red at some point during their lives, but it’s most likely Aspergillus due to its prevalence. If you find red mold on food, however, that is probably Neurospora.
Orange mold is similar to Serpula lacrymans in that it is a fast-growing mold that can cause serious damage to wooden structures over time. It’s often found on wooden surfaces inside or outside the home like tables, chairs, beams, and floors. Exposure to orange mold may aggravate asthma and other respiratory conditions, but it usually poses little to no health risk.
Brown is another color that may be present in several different mold colonies. Many brown molds can spread quickly on harder surfaces, and while they may cause allergies in some, they’re largely safer to be around. Many of these molds have a very musty scent to them. Brown mold can be any of the following types:
- Pithomyces chartarum
- Aureobasidium pullulans
Mucor is the exception to the rule when it comes to brown molds being generally safe to be around. Mucor is a mold type that is very dangerous to be around and can sometimes cause a life-threatening blood infection called mucormycosis. This is one variety of mold that is hard to distinguish because at any point during its life cycle it can be brown, yellow, black, white, or gray.
Test Your Mold
Fungi serve a very important role in ecosystems—the decomposer—and mold is no different. Unfortunately, what is helpful in nature, isn’t always wanted in your home. Mold in the home is doing the same job it does outside, which is why if you find mold of any kind you should address it immediately. Some molds will decompose structural components that can put you and your family at risk, while others are toxic to interact with, but all of them serve as a sign of bigger problems. Identifying mold properly will prevent serious health risks and damage to your home, but unfortunately color isn’t a reliable distinguishing characteristic. The only true way to identify what mold may be growing in your home is to get it tested. Send us a sample of your mold and we will help you determine what next steps you should take. Contact us today to find out more.
Lisa started in the industrial hygiene and environmental industry in 1992 as an asbestos microscopist and began performing building inspections for asbestos, lead paint, and other hazards in 1994.
“This career has been an amazing experience, traveling for work to perform inspections both locally and abroad to locations such as Hawaii and Germany. My real love however is being in the laboratory and assisting our wonderful clients.”