Observing Mold Under Microscope

Mold can be found indoors and outdoors and is a type of fungus. It can come in many colors, including green, black, white, and brown. While most molds are harmless, some can cause health problems. In this blog post, we’ll take a look at how to observe mold under a microscope. We’ll also discuss some of the differences between types of mold. Stay safe!


Fungi is a kingdom in the plant world that contains more than 99,000 species, including yeast, molds, smuts, and rusts.

Fungi are a comprehensive group of organisms that can be single-celled or multicellular and may be found virtually anywhere (particularly in damp environments).

Mold or mould is a form of fungus genetically similar to yeast. Mold, like yeast, is eukaryotic and may be found in damp places. They also decomposers utilize enzymes to break down organic materials (leaves, wood, plants, etc.) that provide energy.

Unlike yeast, these organisms are more plant-like and have long filaments known as hyphae that develop on the surface of the substance being broken down and often cover their entire surface. Given that mold produces via the extension of the hyphae, a mold colony can grow to cover a surface area of several square feet.

Mold can be found on bread, fruits, and other organic items. They’re typically grayish/green or white in color and dusty at times. However, the color of any mold is determined by the type of mold it is as well as the source of nutrients and its age. As a result, they are pretty common indoors and outdoors and are found virtually everywhere.

How Does Mold Reproduce?

Molds can reproduce sexually or asexually to generate spores, like tiny seeds. Sexual reproduction entails mating two different hyphae to form spores, whereas asexual creation via internal division or external modification of a hypha is the case with this organism.

Spores can endure various weather and environmental conditions, such as severe heat and cold, and are frequently carried by air (wind) or water to new locations where they will thrive if the right circumstances exist.

What are the Common Types of Molds?

The most typical kinds of mold include:

  • StachybotrysThe toxic mold mentioned above is often confused with damp, black mildew. It has a slimy texture and is also known as deadly mold since it generates mycotoxins that can contribute to respiratory issues.
  • Aspergillusthis kind of mold has about 300 identified species! They can be found indoors and have been linked to various ear, eye, and respiratory illnesses.
  • CladosporiumThey may be found throughout the year, but they are often seen in the winter. They thrive inside and can even grow in cold conditions. They are frequently observed on textiles, wood surfaces, and flooring boards, as well as causing respiratory problems.
  • MucorMucor is one of the fastest-growing mold species, which may be found on soil and conditioning systems. One of their most distinctive features is a rough texture appearance.
  • AcremoniumThis kind of mold is typically black and may cause allergic reactions that result in congestion, coughs, and skin rashes. It often grows on bread and cheese since it produces carbon dioxide (and therefore needs oxygen to survive). Acremonium may have an immunosuppressant action and a variety of other organ and mental impairments.

Collecting Mold Sample for Observation

Please be aware that we do not suggest this project for individuals who are allergic to mold (including penicillin) or have severe asthma.

The simplest way to produce mold is on a slice of bread. Soft preservative-free bread will do the job. Bread that has been preserved with additives will take considerably longer to grow mold. Allow about an hour for the bread to be exposed to pollutants in the air before storing it indoors.

Place the bread in a ziplock bag and moisten it with water. Seal the bag leaving some space inside. Keep the bag away from other foods in a dark, warm place. A kitchen cabinet near the cooktop may be another possibility. Alternatively, it might be placed near a window with a bowl or plate covering it to keep the light off it. Mold thrives in a humid environment. The appearance of mold will take 2-3 days, but it may take one week or longer to obtain a decent sample.

Every few days, check on the bread and add more water if it becomes parched. To avoid opening the plastic bag as much as possible, avoid touching the bread. After the mold has sufficiently developed, you may make a slide and inspect it using a microscope. You’ll need a piece of mold that is about one inch in diameter.

Good to note: It is recommended to use soft bread without preservatives because mold will take a long time to grow on bread with preservatives. It is also important to avoid inhaling the spores or touching the mold with bare hands, given that mold is an allergen.

Observing Mold Under Microscope

If you have collected a sample of mold to observe, the process is relatively simple.

Here are the things that you will need:

  • Mold sample
  • Plain glass slide
  • Coverslip
  • Water
  • Methylene blue (optional)
  • Disposable gloves


It is critical to cover as much skin as possible while dealing with mold and to use gloves. Mold is ahistamine, which means it can cause an allergic reaction. Mold can be an issue, but you won’t have to worry if you’re a part of the study. People under 21 are most susceptible, followed by those over 70 and persons with severe immune issues. However, this experiment is not for you if you suffer from allergies or asthma.


  1. Place a droplet of water in the center of the slide, whether with an eyedropper or a clean finger. Alternatively, you may use methylene blue solution, a microscope stain that colors specific regions of mold cells, making the sample simpler to see.
  2. Scrape some of the molds off with a toothpick and place it on the drop of water.
  3. Take the coverslip and angle it so that one edge of it touches the water drop, then carefully slide it over the drop of water without trapping air bubbles underneath.
  4. Blot up any extra water with a paper towel at the corners of the coverslip.
  5. Use a compound microscope to examine the slide, starting with the low-magnification objective.


You may increase the visibility of the specimen with a drop of methylene blue.

Many varieties of mold exist. As a result, what is seen under the microscope is highly determined by the sort of mold being viewed.

About Molds When Viewed Under the Microscope

The bread’s colorful mold is composed of connected thread structures called hyphae. These form a mold colony, which was begun by a single mold spore. The mold mycelium may be fuzzy, soft, or colorful. You can identify what kind of mold it is by looking at the hyphae under a microscope.

Bread is a common food for the brown molds that grow on it, such as Rhizopus. It feeds on starch or sugar and may be present on bread. The white hair-like structures of this type of mold begin as white spots before eventually turning solid black. Rhizopus looks like a balloon on a string when seen under the microscope. The head is where the mold spores are found.

Grains and other foods are also susceptible to Aspergillus mold. It’s a bluish-green color, with a thin white ring circling each colony. Some kinds of Aspergillus are black. Make a slide and check it under the microscope to identify this kind of mold. It has a thin branch-like structure with heads resembling blooming flowers and spherical spores released from the top.

Penicillium mold, which is where Penicillin is derived, comes in various colors, including blue-green and gray, with a fuzzy white border. This mold is widespread and typically appears like Aspergillus when seen without magnification. You will find several strand segments branching out from the leading strand of the head if you examine it under a magnifying glass. The head has a thinner structure than Aspergillus, with many strand segments branching out from the mainline. Tiny spores should be visible at the end of each segment of the head.

Some observations regarding the more prevalent indoor molds

Let’s take a step back to discuss black molds and what makes them so dark. These molds, as we do, contain melanin to protect them from UV C in sunlight. The mold may be cleaned off, such as the Cladosporium from a bathroom ceiling. However, the melanin stain will remain. A mold stain remover or paint might be used to remove or cover it.

UV light is not very effective in preventing mold growth on AC coils, although Cladosporium, the most prevalent mold that develops on AC coils, may not be harmed by it.

Aspergillus and Penicillium

These molds are frequently discovered in damp locations such as:

  • damp basements
  • under steps to the basement
  • behind finished basement walls
  • attics with inadequate ventilation and too much moisture, plumbing, or roof leaks
  • inside sink cabinets
  • below-grade on wood or OSB (oriented strand board) in new construction
  • AC coils and in contaminated ductwork
  • ceilings and insulation in damp crawl space
  • growing on books and clothing stored in basements
  • furniture in houses shut up in a humid season

The general term for these molds, “Aspergillus or Penicillium-like,” is also used because Aspergillus and Penicillium spores appear similar, and distinctive fruiting bodies aren’t always visible. A half-dozen stray spherical spores on a tape sample may not always indicate whether they come from Aspergillus or Penicillium (another mold producing round spores).

The health effects of Aspergillus or Penicillium may be similar. There may be allergic or asthmatic reactions if a few spores are breathed in. If there is a lot of development and gases are breathed in, headaches, sadness, or mental sluggishness may result. At home, being on alert may put your immune system at risk.

Both molds have various colors when growing on a Petri dish, ranging from green to white, orange, yellow, or black (Aspergillus niger).

Under a microscope, you’ll notice a variety of distinctions such as:

  • size and texture of the mold spores
  • how much dye do they absorb
  • width, texture, and segmentation of the hyphae
  • differences in size, shape, and surfaces of the structures that produce the spores

It’s these aspects that a laboratory technician examines to assist in mold type identification. However, science is progressing, with computerized DNA testing becoming more accurate and delivering results faster, at a higher cost.


Alternaria is a blackish-brown mold that causes asthma or an allergic reaction. Chronically wet wood is often the source of this fungus.

If you have a water leak at home, better check for mold growth in wooden areas around it. It can lead to frequent respiratory illness, asthma attacks, and other allergies.

You can see in the pictures that Alternaria has a slimy, black surface. The spore is also nearly round and smooth with a wavy edge. Its size is about 10-15 micrometers. The mycelium is septate and branched.

Stachybotrys chartarum

This so-called “toxic black mold” is a greenish-black mold found worldwide. It grows on materials with a high cellulose content, such as paper, wood, and building materials.

chartarum produces large amounts of mycotoxins, which are poisonous and may cause severe health problems in people exposed to them. The most common symptoms of Stachybotrys exposure are respiratory problems, such as wheezing, coughing, chest tightness, and eye irritation.

Like other types of molds, Stachybotrys grow in moist environments. They are likely to flourish in areas with a leak or have been flooded.

Stachybotrys has been linked to pulmonary hemorrhages in infants. There is evidence of long-term neurological damage caused by chronic mycotoxin exposure from some Stachybotrys species. 

Source: molekule.science


Chaetomium is a mold that is found both indoors and outdoors. It can be white, cream, yellow, or light brown. Chaetomium reproduces by producing spores that are released into the air. This mold can cause skin and eye irritation.

It isn’t easy to distinguish between Chaetomium and Cladosporium, which are very similar. The spores of both molds are elliptical, and their dimensions are about the same.

This mold is most commonly found on a few rafters in the attic or some ceiling joists in the basement. It’s usually dried-out mold, particularly in the attic. Under the microscope, you’ll find broken-up hyphae with no spores. It’s non-viable mold because it can’t develop again. However, a dark stain may remain if you use Borax solution to scrub it off.


This mold is found both indoors and outdoors. It can be gray, green, brown, or black. Cladosporium reproduces by producing spores that are released into the air. This mold can cause skin and eye irritation.

Cladosporium is most commonly found on the surface of water-damaged materials, such as ceiling tiles, walls, wood, and textiles. It often grows in large, light- to dark green or gray colonies. Under the microscope, you’ll find spores that are elongated oval-shaped with black dots on either end. They may also appear as bi-cellular spores, shield, banana, or torpedo-shaped spores.

Cladosporium is a black mold that thrives in high temperatures, moist air, and cool places. It may grow on many surfaces, including windowsills and bathroom ceilings, top corners of closets on an outside wall, AC units or their insulation, and attic sheathing if there is too much moisture with insufficient ventilation.

Cladosporium is invariably found in room air because it is a common outdoor mold. However, it does not give off spores like Penicillium or Aspergillus indoors. 


Trichoderma is a fast-spreading green mold that can produce trichothecenes and thrives in greater moisture, if not wetness.

Green bunches of tiny clumped spores, which may be likened to clusters of tiny grapes, are common tell-tale indicators of Trichoderma under a microscope. The spore development occurs from pyramidal-shaped branches that appear at the end of the central stalk.


Ulocladium is a black mold that thrives in damp conditions and can grow on the sheathing of leaky attics. It has covered the underlayment in an attic with poor ventilation. Brown spores are cigar-shaped and resemble hand grenades.

After Observation Clean Up Protocol

When the experiment is completed, seal the bread and anything that came into contact with it in a heavy-duty plastic zip lock bag, then dispose of it. The slide will not be permanent, so make sure to dispose of it after usage. Clean the location you were working in with bleach wipes (such as Clorox) or soap and water thoroughly.


Many types of mold can be found in both indoor and outdoor environments. Each mold has a different appearance, and some can cause skin and eye irritation. Some molds, such as Stachybotrys, can also cause long-term neurological damage. It is essential to identify different types of mold to clean them up properly.

Under the microscope, you can see that mold has a variety of shapes and sizes. Some mold spores are elliptical, while others are elongated oval. You can also see that some molds thrive in high temperatures and moist air, while others grow in cool places with less moisture. By observing mold under a microscope, you can better understand how to clean it up and prevent it from spreading.


Last update on 2024-06-12 / Affiliate links / Images from Amazon Product Advertising API

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