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The Causes and Effects of Mould in Your Home

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The Causes and Effects of Mould in Your Home

By Ruth MacEachern

Product Manager

Jul 31, 2023

If you discover mould in your home, you need to act quickly to remove it and then take steps to prevent the mould coming back. Mould spores are an allergen that can cause reactions in people with weak immune systems and respiratory conditions including asthma, and some species of mould release toxic chemicals called mycotoxins that can cause major health problems in children and older people.

The health risks of mould

Allergic reactions to mould can range from mild to severe and include:

  • Skin rashes
  • Depression
  • Fatigue
  • Difficulty breathing
  • Eye irritation

If the mould spores are inhaled, they are more likely to cause problems in your respiratory tract and can trigger an asthma attack in people with the conditions.

Mould usually grows in damp conditions, and these are also associated with worsening underlying heath problems, so the longer the mould is allowed to persist, the more serious the reaction is likely to be.

With toxic black mould, the presence of mycotoxins can also result in long term problems.

What Causes Mould to Grow

Mould grows from microscopic spores that are carried in the air. Mould spores are present in every home, but they will not develop into colonies unless the conditions are right. If the mould spores land in a damp area with limited air flow to move them on, they will start to grow almost immediately.

The damp that allows mould to grow in the home is often a result of high humidity in the air. Water vapour from bathing, cooking and even breathing will form condensation on cold surfaces and as this is absorbed into plaster and wood, it will cause damp. It is this damp where the mould will usually grow.

Different types of household mould

Mould is a type of fungus which grows from spores. The spores spread across a surface using thin filaments that create a network called a mycelium. The filaments that connect the mould together are called hyphae and in effect, the whole colony of mould is a single organism. There are countless species of mould in the world, although only a few of these are seen in British homes.

Moulds can grow on almost any porous surface where there is some moisture and the most common species of mould that may be found growing in houses are:


This species can be found in darker areas such as under sinks and in cupboards. It prefers warm conditions and will spread most during the summer months when it is warm and humid.


Aspergillus will often be found in dusty environments. Damp patches in plasterboard can provide the ideal conditions for it to grow and it is common on walls.


You are most likely to find Cladosporium on softer surfaces including fabrics and wood. It grows below the surface and creates patches that are difficult to spot until it is ready to release spores.

Stachybotrys Chartarum

Also known as toxic black mould, this species can form large black patches in areas with a lot of moisture such as bathrooms. Stachybotrys Chartarum may need to be professionally cleaned.

How can you remove mould?

It is quite simple to clean mould from surfaces in your home. Dilute bleach with water at a ratio of one part bleach to four parts of water and then spray onto the mould. This will kill off the surface mould and allow you to wipe it away.

When using bleach or supermarket mould cleaner, it is important to work in a well-ventilated space and to wear gloves, mouth, and eye protection. Dispose of any cloths that you use in the bin to avoid spreading spores elsewhere in your home.

Unfortunately, mould cleaners will only remove the mould from the surface, and it can quickly grow back if the damp conditions remain.

To stop mould for good, you will need to take away the source of moisture. In most homes, condensation from cooking, bathing and drying clothes indoors causes an increase in humidity. Improving the airflow in your home will reduce condensation, and excess moisture can be removed from the air using extractor fans in your bathroom and kitchen.

Can we help

Mould in your home can pose a threat to your health if it is allowed to grow. Preventing condensation reduces the damp conditions where mould can grow, and better ventilation will help. If you are concerned about the presence of mould in your home, please contact us today. Our local ventilation specialists can visit your home to conduct a free survey that will identify the causes of mould. Enter your postcode below to find an expert near you.