What Causes Mold and Mildew?

What Causes Mold and Mildew?

Mold and mildew develop when moisture combines with conditions that allow fungi to grow. Damp surfaces, high humidity, poor ventilation, condensation and water leaks can all contribute to mold and mildew problems around the home.

Bathrooms, showers, basements and other areas that frequently remain damp are particularly susceptible.

What Does Mold and Mildew Need to Grow?

Moisture is one of the most important factors.

Common sources include:

• High humidity

• Plumbing leaks

• Condensation

• Poor ventilation

• Water intrusion

• Standing water

• Wet building materials

• Surfaces that don't dry completely

Mold can also grow on or around organic material and residue found in everyday environments.

Why Does Mold Grow in Bathrooms and Showers?

Bathrooms frequently provide the warm, humid conditions associated with mold and mildew growth.

Every shower or bath adds moisture to the room. If that moisture isn't removed through ventilation and drying, surfaces may remain damp for extended periods.

Common problem areas include:

• Shower walls

• Tile and grout

• Bathtubs

• Shower curtains

• Corners and seams

• Areas around fixtures

• Window areas

Running an exhaust fan and allowing surfaces to dry can help reduce excess moisture.

Why Does Mold Grow on Grout?

Grout can be more porous than surrounding tile, allowing it to retain moisture.

Soap residue, body oils and other material may also accumulate along grout lines.

The combination of moisture and residue can make shower and bathroom grout particularly prone to recurring mold and mildew staining.

Why Does Mold Grow in Basements?

Basements can experience persistent moisture because they are partially or completely below ground.

Potential causes include:

• High humidity

• Groundwater intrusion

• Foundation leaks

• Condensation

• Plumbing leaks

• Poor ventilation

• Damp concrete

A dehumidifier, improved ventilation or correcting the source of water intrusion may be necessary when basement moisture is persistent.

Can Mold and Mildew Grow Outdoors?

Yes. Outdoor surfaces can also develop mold and mildew staining.

Conditions that may contribute include:

• Frequent rainfall

• Shade

• High humidity

• Poor drainage

• Standing water

• Limited sunlight

• Surfaces that remain damp

Concrete, stone and other outdoor surfaces may be particularly susceptible in shaded or poorly drained locations.

What's the Difference Between Mold and Mildew?

Mildew is generally a term used for certain types of surface fungal growth, while mold is a broader term covering many different fungi.

For everyday household cleaning, both may appear as unwanted staining or growth on moisture-prone surfaces.

Regardless of terminology, controlling moisture is one of the most important steps for reducing recurring problems.

Why Does Mold Keep Coming Back After Cleaning?

If mold or mildew repeatedly returns, the conditions that caused it probably still exist.

Cleaning can remove visible surface staining, but it doesn't repair a leaking pipe, lower excessive humidity or improve poor ventilation.

If the same area repeatedly develops mold or mildew:

1. Identify the source of moisture.

2. Correct leaks or water intrusion.

3. Improve ventilation.

4. Reduce excessive humidity.

5. Clean the affected surface.

6. Allow the area to dry thoroughly.

How Can You Help Prevent Mold and Mildew?

The key is keeping moisture under control.

• Repair plumbing leaks promptly

• Use bathroom exhaust fans

• Improve ventilation

• Control indoor humidity

• Dry wet surfaces

• Remove standing water

• Address condensation

• Improve outdoor drainage

• Clean moisture-prone surfaces regularly

Cleaning and moisture control work together. Cleaning addresses existing surface staining, while moisture control helps reduce the conditions that allow mold and mildew to return.