We’re often asked, “What is a normal outdoor mould level?” Unfortunately, there isn’t a simple, one-size-fits-all answer. Outdoor mould levels vary based on several environmental factors, but here’s a general guide to help you understand what influences them.
Factor 1: Geography and Climate
The UK has a diverse climate and landscape, meaning mould levels can differ significantly depending on your location. The natural environment around your home - including vegetation, soil type, and humidity - affects the type and concentration of mould spores in the air.
Even within a small area, outdoor mould levels can vary due to micro-differences in terrain, airflow, and local conditions. For example, mould levels in one area may be completely different from those just a few kilometres away. Additionally, outdoor mould levels fluctuate constantly. If you take a sample outside your home now and another in two hours, the results may differ due to changes in wind direction, humidity, or even a neighbour mowing their lawn.
Factor 2: Seasonality
Mould levels also change with the seasons. What’s considered “normal” on a warm June day in London will be very different from a cold January day. Outdoor mould levels typically range from ~100 to 20,000 spores/m³, but factors like wind, rainfall, temperature, and larger weather patterns all impact the concentration of airborne mould spores at any given time.
Because outdoor mould levels are constantly shifting, it's important to view test results as a snapshot in time rather than a fixed measurement. Understanding these natural variations can help you interpret outdoor mould readings more accurately.
