Health Risks Associated with Different Mould Species

Not All Moulds Are Equal — But All Deserve Attention

There are thousands of known mould species, and many remain unidentified. While media attention tends to focus on "black mould," the reality is more nuanced. Different species carry different health implications, and understanding these distinctions is essential for housing providers, landlords and tenants.

Key Species and Their Health Associations

Stachybotrys chartarum

Often called "black mould," Stachybotrys is strongly associated with water damage and prolonged dampness. It produces mycotoxins that have been linked to respiratory issues including asthma, bronchopulmonary disorders and allergic reactions. The BSRIA TG 26/2024 guide notes that prolonged exposure to high concentrations of its spores and fragments can have toxic effects on human health.

Aspergillus

Species within the Aspergillus genus are frequently found in moisture-damaged buildings. A. versicolor is listed in BS ISO 16000-17 as an indicator of moisture imbalance in a property — it's often among the first moulds to colonise when humidity is elevated over time. High exposure can lead to Aspergilloma or Aspergillosis, conditions that particularly affect immunocompromised individuals and those with pre-existing respiratory conditions.

Penicillium

Penicillium species are extremely common indoors and are associated with allergic responses and respiratory irritation. While less feared than Stachybotrys, persistent exposure in damp environments can still cause significant health problems, especially in vulnerable populations.

Cladosporium

One of the most common outdoor and indoor moulds, Cladosporium typically triggers allergic reactions including hay fever-like symptoms, skin rashes and asthma exacerbation. It can grow on a wide range of surfaces and at lower temperatures than many other species.

Who Is Most Vulnerable?

While mould exposure can affect anyone, certain groups face heightened risk. Young children, the elderly, people with asthma or chronic respiratory conditions, and those with weakened immune systems are particularly susceptible. The NHS identifies damp and mould as contributors to respiratory problems across all age groups.

The tragic death of two-year-old Awaab Ishak in 2020 — caused by prolonged mould exposure in social housing — underscored the potentially fatal consequences of inaction. This case led directly to Awaab's Law, which came into force in October 2025.

The Mould UK Approach

At Mould UK, we provide comprehensive lab-verified mould reports that identify the specific species present in a property. This evidence-based approach moves beyond guesswork and gives housing providers actionable data to protect their tenants' health. Our CPD-accredited tenant training also helps residents understand the risks and take practical steps to reduce exposure.