Mold Control on a Budget


Aspergillus, Penicillium, Alternaria, and Cladosporium, as well as Stachybotrys, can cause mold symptoms (symptoms from mold exposure).

Why haven't we heard much about Aspergillus, Penicillium, Alternaria, and Cladosporium? My guess is that there are no dramatic stories about someone who got Aspergillus growth in his or her lungs and who won a huge legal settlement. These stories are out there but the media hasn't caught up with them. I imagine it would be hard to "prove" which exposure caused the infection. Consequently, the media and the public think "toxic black mold" when attention turns toward mold again.

Here's a run-down on Aspergillus, Penicillium, Cladosporium, and Alternaria:


Alternaria is another dark-colored mold. Exposure to Alternaria can provoke respiratory and asthmatic symptoms in susceptible persons. I was called by one mother who told me that every time her son went upstairs, he had an asthma attack. I found Alternaria growing in his closet as a result of the shower leak in the adjacent bathroom. The whole shower had to be taken out, because Alternaria was also growing under the shower pan. Alternaria spores are large, club-shaped spores. These spores do not stay airborne as long as the smaller Aspergillus and Penicillium spores.

In a damp basement of a new house, I saw Alternaria visible across foundation walls. That was a first for me.


Aspergillus is a very a common indoor mold that can be found on basement ceilings, at air conditioning coils, at leak areas, on the lower parts of foundation walls, on and under basement steps, on crawlspace ceiling joists and subflooring, at leaky roofs, in flooded areas where humidity has been elevated for an extended time, etc.

Under the general heading of the genus, Aspergillus, there are a couple of hundred species, such as Aspergillus fumigatus, Aspergillus niger, and Aspergillus versicolor. Some species give off mycotoxins, volatile organic compounds (VOC gases), and other byproducts that can be troublesome to susceptible individuals.

Mold symptoms can include headaches, trouble sleeping, itching, rashes, fatigue and other neurological complaints, and respiratory and asthmatic symptoms. One of the worst features of Aspergillus is that it can grow in human tissue. For people with weakened immune systems, this growth can eventually be fatal.

Under a microscope, Aspergillus looks like a flower that gives off strings of beads that are the spores. Spores are spherical, seen either individually under the microscope or present as a string of spores.

An interesting feature about Aspergillus is that it likes OSB (oriented strand board), which is a wood product used in new house construction. Many new homeowners who think they have a dry basement actually have a lot of Aspergillus growth on the basement ceilings and on the stairs to the basement.


Cladosporium is a black mold, though not the "toxic black mold." Cladosporium commonly grows on insulation in AC systems, on bathroom ceilings when there isn't enough ventilation, sometimes on walls and wallpaper in rooms where insulation is lacking, on foundation walls, on basement and crawlspace ceiling joists and subflooring, and on attic sheathing.

Cladosporium, like Aspergillus and Penicillium, is an allergenic mold, though not usually viewed as one of the top allergenic molds. In my experience, the top three most common allergenic molds are Aspergillus, Penicillium, and Alternaria. However, if you're sensitive to Cladosporium, it's one of the top allergenic fungi for you.

In my experience, Cladosporium does not become airborne easily indoors. That is, I have seen rooms where Cladosporium is visible on walls and ceilings, yet it did not show up in air samples. Conversely, some geographic areas have high levels of Cladosporium in outdoor air. If people open their windows, plenty of Cladosporium spores will blow in. These spores blow in; they blow out; they get picked up in vacuuming and dusting. It's no big deal, unless you are allergic to them or less your home is damp, and they can start growing. Sometimes I see Cladosporium growing in a film across attic sheathing (the roof deck) because moisture from below gets trapped in an attic that doesn't have good ventilation.


Penicillium is green bread mold but also grows in other places of the house, such as in an AC system, at leak areas, and flood areas where humidity has been elevated for an extended time, on shoes and furniture in a damp basement, etc.

Some people are allergic to Penicillium. Symptoms from mold exposure can be similar to those of Aspergillus. Under the microscope, spores from Penicillium are also spherical. You need to see the growth structure that produces the spores to distinguish them from the spores of Aspergillus. Penicillium growth structures appear brush-like, with strings of beads coming off the ends of the brushes.

More Common Black Fungi

I'll just mention a few more black fungi to illustrate that not all black molds are Stachybotrys. I've already mentioned three dark molds (Cladosporium, Alternaria, and Aspergillus niger) that are not Stachybotrys. Aspergillus can be a variety of colors, mostly green or white, but Aspergillus niger is black.

Here are some more:

Chaetomium - an allergenic mold that likes leak areas. Chaetomium grows happily on wood and on drywall. Sometimes when I look closely at Chaetomium, the growth appears to be in miniature mountains. Stachybotrys growth is more flat, even velvety. Under a microscope, Chaetomium looks like a large spider, with lemon-shape spores forming inside the body of the spider. Eventually, the body splits and spores pour out.

Another common place to see Chaetomium is in splotches of black on wood beams in attics and basements. This Chaetomium typically is left over from the time of construction and is often non-viable (dead). Occasionally I see significant viable Chaetomium on relatively new lumber in the basement.

Ulocladium - an allergenic mold that likes leak areas. I've also seen Ulocladium growing across attic sheathing in an attic with too much humidity. Under the microscope, Ulocladium spores kind of look like elongated segmented berries.

Fungi in areas of chronic dampness

Mucor, Rhizomucor, and Trichoderma - These fast-growing fungi can be troublesome to sensitive individuals. I remember reading an article on Mucor years ago where it had gained foothold in a woman's sinuses and migrated through her body, proving fatal. While this may be a rare occurrence, any such anecdote is just another reminder to take mold seriously and get rid of all mold growth at home.

After all this biology, let's think about a take-home lesson:

You don't usually need to know what genus or species of mold is present. Getting rid of the mold solves the identification question!

The exception to this is if your physician needs to know the genus or species for treatment purposes. ("Aspergillus" is the genus. "Aspergillus versicolor" is the species.)

If identification of species is required, that would involve a microbiological laboratory. To find a certified laboratory, go to the website of the American Industrial Hygiene Association, Scroll down to "Laboratory Programs" on the left. and then click on "Find an Accredited Lab" at the upper right.

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Updated 9-2011