Common Household Molds and Their Hazards

Mold is a type of fungus that thrives in warm, humid, and poorly ventilated environments. It is commonly found in kitchens, bathrooms, basements, window frames, walls, carpeting, and even on food. While certain molds play a positive role in medicine and food production—such as the production of penicillin and some cheeses—most household molds can negatively impact your health.

Mild exposure may cause symptoms like sneezing, runny nose, skin irritation, rashes, or itchy eyes. Prolonged or heavy exposure, particularly to molds that produce mycotoxins (such as Aspergillus flavus), can pose more serious risks, including respiratory infections, allergic reactions, liver or kidney damage, immune suppression, and even an increased risk of cancer.

Common Types of Household Molds

1. Aspergillus

Aspergillus is one of the most common molds in the home. It prefers damp, warm, poorly ventilated areas, such as wall leaks, bathroom corners, basements, around window frames, and on air conditioning system filters.

Black Aspergillus:

Commonly found in bathrooms and around kitchen sinks, wall seeps, and window sills. It is often black or dark brown and forms large patches. It may cause sinusitis or airway irritation.

Aspergillus fumigatus:

It is commonly found in damp corners of bathrooms, window frame crevices, ventilation systems, and dust. Its spores are tiny and can become airborne. Aspergillus fumigatus is the most common pathogenic Aspergillus and can cause respiratory allergies or pulmonary aspergillosis, making it particularly dangerous for people with weakened immune systems.

Aspergillus flavus:

Grows on damp walls, window frames, and wet grains and nuts. It is yellow-green in color and can produce aflatoxins. Long-term exposure can cause liver damage.

Aspergillus versicolor:

Commonly found in walls, wood, dust, and ventilation ducts, it varies in color, ranging from green to blue to gray. It produces sterigmatocystin, a steroidal mycotoxin that is potentially carcinogenic to long-term exposure.

2. Penicillium

Penicillium is the most common type of fungus and thrives particularly well in damp, dark environments. It prefers to attach to organic matter or porous surfaces, appearing as bluish-green, gray-green, or white hairs.

Penicillium citrinum

Commonly found on damp walls, window frames, books, and carpets, it appears as bluish-green or gray-green hairs. It produces citrinin, a fungus that can damage the kidneys.

Penicillium variabile (P. chrysogenum)

It is commonly found on bathroom walls, moldy spots, and wooden furniture. It appears as bluish-green or grayish powdery spots. It can produce mycotoxins and cause allergies.

Penicillium expansum

It is commonly found on the skin of fruits like apples and pears that have been stored for too long, as well as on damp areas like kitchen countertops and windowsills. It has a pale green or bluish-green appearance and a musty odor. It produces ochratoxin (patulin), which is harmful to the stomach, intestines, and liver.

3. Cladosporium

Cladosporium is one of the most common indoor molds, found in the air, on plant surfaces, in soil, and in moist environments around the home. Its spores are easily spread through the air, making them common in our daily lives.

Cladosporium cladosporioides

It is commonly found on walls, textiles, wooden furniture, and in airborne dust. It thrives in poorly ventilated, high-humidity environments. Its colonies appear dark green to olive-colored, powdery or velvety, often with scattered small black dots or flaky patches. Its spores are common aeroallergens, potentially causing sneezing, runny nose, itchy eyes, and rashes. It is particularly harmful to asthma sufferers, potentially exacerbating respiratory symptoms.

Cladosporium herbarum

It can be found both indoors and outdoors, particularly on damp walls, windowsills, bathroom tiles, around radiators, and on decaying leaves and plant debris outdoors. It typically forms a loose, brownish-green or dark green mold layer. It is one of the most common indoor allergenic molds, particularly affecting those with sensitive respiratory tracts, often triggering allergic rhinitis, asthma, and coughing. Long-term exposure can lead to chronic respiratory inflammation.

Cladosporium sphaerospermum

It is often found in bathrooms, kitchens, basements, air conditioning filters, and ventilation systems. It can also be found in refrigerators and on food surfaces. Its colonies are typically dark brown or black with a rough surface, often clinging to plastic, wood, and glass. It can cause pharyngitis, coughing, and allergic reactions, potentially leading to fungal sinusitis or lung infections.

4. Alternaria

Alternaria is a common mold found in the air and indoor environments, particularly in damp, poorly ventilated environments. It is often airborne, with large spore counts, making it a significant indoor and outdoor allergen, with significant impacts on respiratory health.

Alternaria alternata

This fungus often appears on damp walls or rotting fruits and vegetables, forming black or dark brown, fuzzy colonies. It can cause allergic rhinitis, asthma, and skin inflammation. In people with weakened immune systems, it can cause lung infections.

Alternaria tenuissima (Alternaria parviflora)

Commonly found on outdoor plant leaves and pollen, as well as indoor wood and fabric products, it often forms thin, dark brown or black mold patches in damp corners. It can aggravate asthma or allergy symptoms. Some fungi also produce mycotoxins, which are harmful to health.

Alternaria infectoria

This fungus is commonly found in improperly stored grain and on damp indoor surfaces such as walls, wood, and building materials. Its colonies are dark green or black and are associated with eye, nasal, and skin infections, making it particularly susceptible to illness in immunocompromised individuals.

5. Stachybotrys chartarum (Black Mold)

Alternaria is one of the most common indoor and outdoor molds and is very common in everyday environments. It particularly prefers damp, poorly ventilated areas and can be found in homes, schools, offices, and other places.

Alternaria alternata

It is commonly found on damp walls, bathroom tiles, window frames, air conditioning filters, and basements, often forming black or dark brown ring-shaped or large patches of black mold. It is one of the most common airborne allergens, causing allergic rhinitis, asthma attacks, and skin inflammation. People with weakened immune systems may also develop respiratory infections.

Alternaria tenuissima

Commonly found in damp corners, wooden furniture, textiles, curtains, paper, and dust. Its colonies appear as dark, powdery or fuzzy colonies that easily adhere to fabrics and walls. It is often associated with asthma and allergic rhinitis; it can produce mycotoxins, posing a health risk with long-term exposure.

Alternaria infectoria

This mold is commonly found on damp walls, ceilings, ventilation ducts, and improperly stored grain and paper. It appears as dark green to black mold spots and can persist on building materials and in indoor environments. It is often an allergen in immunocompetent individuals, but can cause sinusitis, keratitis, or lung infections in immunocompromised individuals.

The Importance of Professional Treatment

If you discover large-scale mold contamination (e.g., walls, ceilings, carpets, or furniture covered in mold), do not attempt to clean it yourself. During removal, mold spores and toxins can easily spread into the air, creating an even greater health hazard.

In such cases, it is strongly recommended to contact a licensed professional mold remediation service. Qualified specialists have the equipment, protective gear, and expertise to safely detect, remove, and prevent mold, ensuring a healthy environment for you and your family.