Different types of molds can grow in a person’s home. Mold can grow on walls, clothes, books, toys, and more. Mold can damage household items and it may also cause health issues.

Whether it is a cold, damp winter or a warm, humid summer, activities at home can result in moisture indoors and the appearance of mold in the house. This can affect a person’s health, including causing breathing problems, triggering allergies, and more.

This article looks at what mold is, why it grows, its impact on a person’s health, and how to stop it.

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Molds are a form of fungus. There are many different types, and they can occur both indoors and outdoors.

Molds produce spores, which spread by floating around in the air. Mold spores are present in all indoor environments. There is no way to completely prevent spores, and they can persist in conditions where mold itself cannot grow.

Mold spores thrive in environments that are moist and warm. When they land on a damp spot they begin to grow.

Molds can grow on a variety of different surfaces, including fabric, paper, wood, glass, and plastic. As they grow, they may digest the material they are growing on.

Many different types of mold can grow in the home. Common indoor molds include:

  • Cladosporium: This can grow in either cool or warm areas. It may appear on fabrics and wood surfaces.
  • Aspergillus: This often grows indoors, on dust, powdery food items, and building materials, such as drywall.
  • Penicillium: This tends to grow on materials with water damage. It often has a blue or green appearance.

Molds take a variety of forms and textures. They can be white, black, yellow, blue, or green. They may look like discoloration or stains on a surface.

They can also have a velvety, fuzzy, or rough appearance, depending on the type of mold and where it is growing.

Mold spores are everywhere, both indoors and outdoors, but they are not visible to the naked eye.

Spores can enter the home either through the air or by attaching to objects or people.

Mold will only flourish if spores land somewhere with the ideal conditions for growing, such as moisture and a supply of suitable nutrients.

Places where mold often appears include:

  • areas where leakages and flooding have occurred
  • windows where condensation builds up
  • places where the air does not circulate

Wet cellulose materials are most supportive of mold growth. Examples include:

  • paper products, including wallpaper
  • cardboard
  • ceiling tiles
  • wood products
  • insulation materials
  • upholstery and other fabrics

Mold can pose a health problem, especially for people with:

  • an allergy
  • an existing respiratory problem
  • a weakened immune system.

Breathing problems

As mold grows, spores, cells, fragments, and unstable organic compounds can enter the air. They can produce allergens, irritants, and mycotoxins.

Some of these can be toxic, especially to individuals who have a sensitivity to them.


A person with a sensitivity or allergy to any mold-related particles may react to the mold.

Mold allergies can produce similar symptoms to other allergies, such as hay fever, or seasonal allergy.

Symptoms include:

People with a mold allergy as well as asthma have a higher chance of having an asthma attack when there is mold in the environment.


Aspergillus can cause a serious health problem known as aspergillosis.

Most people can breathe in the spores of this fungus without becoming sick. However, people who have a weakened immune system or an existing lung condition can have a severe reaction.

There are different types of aspergillosis:

  • Allergic bronchopulmonary aspergillosis (ABPA): This affects the lungs and can cause symptoms such as wheezing, coughing, and shortness of breath.
  • Allergic aspergillus sinusitis: This affects the nose and can involve stuffiness, a runny nose, and a headache.
  • Aspergilloma (fungus ball): This can cause a cough, which may produce blood, as well as breathing problems.
  • Chronic pulmonary aspergillosis: This can cause breathing problems, a cough, fatigue, and unexplained weight loss.

Other conditions

Mold can trigger the production of microbes and bacteria. Exposure to these bacteria may trigger an inflammatory response in some people

There is some evidence that it may lead to hypersensitivity pneumonitis, a type of lung inflammation.

Mold exposure may also trigger sinusitis, which refers to inflammation of the sinuses.

People may experience the following symptoms after spending time in an environment where mold is present:

Controlling moisture is the key to preventing mold from growing indoors. It is also important to keep the home clean and well ventilated to reduce humidity.

The Environmental Protection Agency (EPA) advises people to aim for a humidity level of below 60%.

People can reduce the risk of a buildup of moisture and mold by:

  • acting quickly if a leak or spillage occurs
  • using a dehumidifier to reduce indoor moisture
  • leaving windows open when possible, to allow air to circulate
  • using extractor fans to remove moisture during cooking
  • avoiding indoor activities that produce moisture, such as drying clothes or using kerosene heaters
  • ensuring that all fabrics are thoroughly dry before storing them
  • emptying and airing rarely used drawers and closets from time to time
  • regularly cleaning so that mold cannot build up on surfaces, dust, or other matter
  • using mold-killing products when cleaning the bathroom
  • avoiding laying carpets in bathrooms and basements
  • maintaining buildings, facilities, gutters, and drains to reduce the risk of leaks

It is not always possible to prevent mold from growing, but regular cleaning and wiping can reduce the risk of it appearing or getting worse.

Various steps may help a person to remove mold.

Wipe hard surfaces with a suitable commercial product, soap and water, or a heavily diluted bleach solution. Always dry the surfaces after use to prevent mold from reappearing. Always wear non-porous gloves and protective eyewear when working with bleach.

The Environmental Protection Agency (EPA) recommends that a person also wears an N-95 respirator when cleaning mold to help avoid inhaling mold spores.

Wash or wipe porous surfaces and check regularly to see if mold has returned, as it can infiltrate these materials. If mold continues to reappear, consider disposing of these items.

To help prevent mold from returning, ask the local hardware store about antifungal paints and other products that can help prevent mold from developing.

In cases of large areas of mold, it is best to call in a professional mold removal service.

Here are some frequently asked questions about mold in the home.

How harmful is mold to humans?

If there is a lot of mold in a person’s home or in another indoor environment, it may be harmful to a person’s health. This is particularly the case if a person has a weakened immune system or an allergy.

Is it OK to have mold in your house?

It is OK to have some mold indoors, according to the United States Environmental Protection Agency. However, mold in the home can negatively affect a person’s health if it lands on damp or wet areas, as this is the ideal environment for growth.

What are the signs of mold sickness?

Exposure to mold in the home can cause symptoms such as sneezing, a runny nose, eye itchiness or irritation, breathing problems, and more. It is important to contact a doctor for advice if a person has concerns about mold sickness.

What creates mold in a house?

Mold in the home happens when mold spores enter the house, either through open areas or when something carries them inside. If the mold lands on a damp surface, it can begin to grow.

All indoor environments have some mold spores in them, but this does not affect most people.

However, people with a compromised immune system may have a higher risk of illness, including lung problems, if there are mold spores and mold in the environment. Others may experience allergic reactions.

Keeping an indoor space clean, dry, and well ventilated is the best way to prevent mold from developing.

Anyone who has concerns about health issues related to mold in the home should contact a doctor for advice. They may also wish to contact a professional mold removal service if mold in the home covers a large area or if it is difficult to remove.