What is mould?

Most of us can point to the black stuff growing in our shower and say: ‘That’s mould.’ Fewer people can say what mould actually is. There are thousands of different species of mould that all spread through spores.

Some of these moulds can cause significant health concerns, ranging from allergies to asthma attacks, and even fungal infections in immunocompromised people. Understanding what mould is, and how it grows, is the first step towards preventing it from growing and spreading in your home.

What is mould?

Mould is a type of fungus that grows mainly on organic matter, and is essential for the process of decomposition. Mould is typically green or black, though its colour can be affected by the nutrient source it’s growing on. For example, mould that grows on vinyl will often have bright purple spots as it absorbs pigments from the material. It’s impossible to identify mould from its colour or growth pattern alone.

How does mould spread?

Mould is made up of tiny, thread-like structures called hyphae. These structures act as the mould’s root system and can spread out far beyond what you can see when you see a mould spot. Once a mould has gotten enough nutrients, it will form fruiting bodies and release spores. Each spore is like a seed that can form a new mould colony when it finds suitable living conditions.

A single mould colony can produce millions of spores that are carried by air currents to new locations. Spores have hard outer casings that protect them from UV, dry conditions, and low and high temperatures unsuitable for mould growth. Once a spore finds a place with optimal conditions to grow, the outer shell will open up, and the spore will send out hyphae to colonise the new area.

Types of mould

There are thousands of different species of mould, each with its own preferred living conditions. Most of these moulds grow outdoors, but when they find their way into your home, they can cause potentially dangerous health issues. The most common species of mould found in homes are from the genera Cladosporium, Penicillium, and Aspergillus. There are also several other, less common genera, such as Acremonium and Stachybotrys, which are notable because they secrete toxins that can cause liver failure and even depression.

What is the health impact of mould in your home?

In terms of health concerns, mould can be divided into three broad groups, depending on how they produce disease:

• Pathogenic moulds cause health concerns by growing on, or in, the person affected. Healthy people usually don’t have to worry about being infected by moulds, but immunocompromised individuals are susceptible to pathogenic mould infections.
• Allergenic moulds cause allergies and allergic reactions, usually through their spores. Many people are allergic to mould spores, and when concentrations of these spores increase, so too do asthma attacks and other allergic symptoms.
• Toxigenic moulds secrete compounds that are toxic to humans. These mycotoxins are an evolutionary survival mechanism that helps moulds fight off competitors such as bacteria and other fungi. Most antibiotics, such as penicillin, are derived from mycotoxins secreted by moulds. Unfortunately, some mycotoxins can be deadly when ingested or inhaled. The most common form of mycotoxin poisoning comes from animals eating mouldy hay, which results in liver failure and death. It’s unlikely that your common shower mould is going to secrete toxins that kill you, but the infamous black mould (Stachybotrys) may cause unusual health conditions such as memory loss.

The most common health impact mould will have is exacerbating existing allergies. Mould colonies shed millions of spores, enough to make a difference in your air quality at home. A higher concentration of spores will lead to more irritation of your immune system, which can increase the severity and duration of your allergic attacks and even lead to chronic symptoms that affect your quality of life. While mould can be difficult to control, doing so can lead to better health outcomes in immunocompromised individuals and a better feeling of overall health for your entire family.