What Is Mould? The Simple Explanation

What is mould exactly? If you’ve ever wondered what mould actually is, how it forms in your home and what dangers it poses, then this extensive article breaks it down in an easy and simple way.

Knowledge is power, as the famous quote goes. Once you understand the ways in which mould forms in your home, then you are better equipped to prevent mould build up from happening in the first place.

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What Is Mould?

Mould is a microscopic fungus. It is naturally in the air all around us, and grows and thrives when specific atmospheric conditions are met (moisture, temperature, and nutrients). Whilst some moulds can be beneficial to our ecosystem (such as breaking down organic material), some mould can be toxic to humans and animals.

Mould floating in the air is invisible to the naked eye. When it comes into contact with a surface, it either dies, or it grows.

Mould forms naturally outdoors, with the breakdown of organic material (including food). Weather conditions then cause the mould spores to float through the air and make its way indoors.

For a mould to start growing, it needs three basic things:

  • The correct moisture level.
  • The correct temperature.
  • The correct nutrients.

Like the fire triangle, where for a fire to start it needs oxygen, heat and fuel, if one of the above is missing, the mould will struggle to grow.

If they are all present, then you are more than likely to experience a growth of black or green mould if this triangle is not broken over a prolonged period of time.

We will talk more about these three conditions below.


We can break moisture down into two parts:

  • Moisture that is present in the air (humidity)
  • Moisture that is introduced in a place due to a problem or fault.

Let’s start with moisture in the air. Moisture in the air is naturally occurring. The process of evaporation means that all air carries water particles that is invisible to the naked eye.

In your home, there is natural moisture in the air, but there’s also additional water in the air that you put into the air unwittingly, every single day.

Here’s some common ways you put water into the air in your home every day.

  • Having a shower.
  • Making a cup of tea.
  • Cooking food.
  • Drying clothes.

If we take the second example, of making a cup of tea, and then thinking about it logically, we can see that when the kettle is at the boiling stage, steam (water particles) emits from the spout of the kettle.

what is mould moisture in your home

This steam always rises because it’s hot (heat rises), and when it rises into the air, it then seemingly dissappears.

But it doesn’t dissappear totally. Those water particles are now floating around your home, and will find either disperse into smaller particles around your home, or condense in one place and leave a body of wetness.

To test this, boil your kettle under a kitchen cupboard. Wait for a couple of minutes after the steam has stopped, and then feel under that cupboard.

It’s wet, isn’t it?

Whilst this isn’t problematic in isolation (don’t stop having your cups of tea!), it would become problematic if you boiled your kettle 100 times and kept all doors and windows shut (see: ventilation; below).

What would happen then is the water vapours would form on ceilings and walls, giving mould spores the ideal place to develop, thrive and multiply.

Thankfully, in the time you make 100 cups of tea, logic would say you are at some point going to open a door or a window, giving the chance for the water vapours to have some ventilation and means of evaporating and drying.

Fun Fact: Just breathing whilst you sleep can emit up to 0.2 litres of water into the air.

The other way moisture can be present is through probelm or fault.

If you have leaky windows, doors or exterior walls, or have problems with damp or rising damp, then that also gives mould the best place to develop and thrive.

All of these problems should be rectified as soon as practicable, to eleimante the chance of mould growth in your home.


Mould spores have a ideal temperature range in which they can flourish.

That temperature range is between 16c and 26c.

Yes, it just happens to be the ideal comfort zone for humans.

Whilst we are not going to start altering our home temperatures to below or above these levels, it is important to keep some heat in your home even when you are not there.

If you have a way of setting a minimum temperature in your home, then it is wise to use this, and not allow the temperature of your home to drop below the 16c mark at a minimum.

prevent mould in your home

This is simply because warmth helps to eliminate moisture and condensation (along with ventilation), therefore limiting the potential of mould forming. Constantly lowering and rising temperatures are a reason that mould can form in your home.

Apart from that one task of always keeping your home at a suitable temperature, there really is nothing more you can do with temprature.


Moulds love organic material. Like paper and wood. But it can also feed off things like paint and even the natural oil your skin produces.

Some moulds feed off the bacteria found in food when it decays past a certain point.

In essence, mould does not have a hard time finding nutrients, so this is not something we can actively control.

The Power Of Ventilation

Ventilation is a key part of preventing mould build up.

This is something households can actively manage to prevent the build up of conditions that leads to the formation of mould.

Remember when we talked about making a cup of tea (above)?

In an enclosed space, the boiling kettle produces steam. If the steam has nowhere to go, when it cools it turns back into water. This water will cover ceilings, doors, cupboards and even floors – basically any surface it comes into contact with. in time, this build up will lead to moisture in your home, therefore providing ideal conditions for mould to form.

If it’s not in an enclosed space, with good air circulation, this steam and water vapour can be dispersed into a larger area, with any ventilation methods (such as open doors, windows or extractor fans), taking this moisture away and out of your home.

That is why proper ventilation is essential to keeping mould growth at bay and is the biggest single thing you can do to prevent mould growth in your home.

What Does Mould Look Like?

The most common type of mould in homes start out as tiny little black or green dots. Left untreated, mould can quickly reproduce spores and grow out of control.

What is black mould

In the image above, the mould growth would have started out as a single, miniscule speck of mould.

Once it starts, it then requires human intervention for it to stop spreading.

Black and green mould are the most common moulds found in homes in the UK, closely followed by white moulds which can sometimes have either a chalky or cotton wool like appearance.

Where Does Mould Form?

Mould will form anywhere where growth conditions exist, as discussed above.

But in homes, the main locations where you might find mould are:

  • On or around windows and doors.
  • On walls.
  • On ceilings.
  • In kitchens.
  • In bathrooms.
  • Behind furniture.
  • On clothing and shoes.
  • Near to where you dry your clothes.
  • In wardrobes.

You may have had a shock when you saw ‘In wardrobes’. But when was the last time you completely emptied your wardrobe? The answer for most of us is ‘never’. We buy a wardrobe (or build one), fill it with clothes, and never empty it again until we either buy new wardrobes, or move home.

But why wardrobes?

It’s very simple. When replenishing your wardrobes after you’ve washed and dried your clothes, if the clothes are not 100% dry, then there is still moisture trapped in them.

This moisture eventually evaporates from the clothes and into the air. The only problem is, there is very little airflow in wardrobes, so the moisture then clings to the sides or rear of your wardrobes, making it the ideal place for mould to form.

If your clothing ever smells, you could have mould growing in your wardrobe.

Health Dangers Of Mould

Mould can produce allergents, irritants and some can even be a toxin and can cause adverse health conditions in some individuals.

Mould can produce symptoms such as runny eyes, runny nose, and can be particularly bad for those with breathing ailments like asthma, or those who are immune compromised or immune suppressed. (Source: NHS Website)

It has also been linked with lung infections and skin diseases, so it is really important that mould is dealt with quickly and effectively.

Quick Tips For Keeping Mould At Bay

Here are some quick tips at reducing the chances of creating ideal conditions for mould to form and grow.

  • Keep your home heated to a minimum of 16c – even if you are away for long periods.
  • Keep your home ventilated by opening doors and windows periodically.
  • When cooking, use lids for pans, and always use any extraction fans you have.
  • Don’t dry clothes on radiators unless you have adequate ventilation (like a door or window partially open).
  • If you dry clothes on a drying rack, have adequate ventilation (like a door or window partially open).
  • When showering or bathing, make sure the extractor fan is on and the window is partially open.
  • Keep furniture away from walls, leave a gap of at least a few centimetres to promote airflow.
  • Periodically, open all windows in your home for 30 minutes, even in the winter, to let fresh air circulate and ventilate.
  • Deal with any problematic leaks or rising damp quickly and as soon as you discover them.
  • Make a point of opening bedroom windows for a few minutes when you wake.
  • Use a dehumidifier if you feel it is necessary.

What Is Mould Like To Remove?

What is mould like to remove from a surface?

Mould, when caught early, is very easy to remove from most surfaces.

A wet cloth with a small amount of bleach can work wonders for cleaning mould from surfaces such as wood, wallpaper and painted walls, but do remember to test a small area first in case the bleach discolours the the surface you are working on.

SAFETY: It is important when removing mould to wear gloves, a mask, and light eye protection, and to fully vent the area you are working in by leaving the doors and windows open.

Sometimes, mould will leave the wall or surface slightly stained, and this is simply evidence that it has found nutrients in the wall (see: nutrients; above), and has begun reproducing spores.

There are many products on the market that help remove mould more efficiently than water and bleach, and some products will prevent mould build up occurring again.


We hope we have answered your question ‘What is mould’ in an organised and simple way.

In closing then, here is a summary of our article What Is Mould?

Mould is a product of nature and the eco system we live in.

Mould can break down things like leaves and other organic material that we no longer need, so it does have its benefits.

Mould growth in our homes though, is an entirely different matter.

Aesthetically, it is not pleasing on the eye. It also produces an unpleasant odour, can lead to health complications and can actually lead to bigger problems such as compromising the structure of your home.

Just doing some simple things like opening windows and using extractor fans whilst we cook can make a massive difference, but if you do notice mould formation anywhere in your home, it is important to tackle the problem head on and deal with it before it bocomes a bigger problem.

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My name is Richard.

I'm 40 years old. And I have nearly 20 years experience in various safety and security industries.

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