Mould inside an AC unit can trigger allergic reactions, worsen asthma, and cause general respiratory irritation in sensitive individuals, and because the unit recirculates air throughout a space, the exposure isn't limited to one area of the home.
Why AC-Related Mould Is Different From Mould Elsewhere
Mould on a bathroom wall stays largely in that room; mould growing on an AC coil or inside ductwork gets actively distributed through every space the system serves, every time it runs. That distribution is what makes AC-related mould a broader indoor air quality issue rather than a localised, contained problem.
Who's Most at Risk
People with asthma, allergies, or compromised respiratory or immune systems are generally most affected by mould exposure, though prolonged exposure can cause irritation in otherwise healthy individuals as well. Infants, young children and elderly family members are typically more sensitive to indoor air quality issues generally.
What to Do If You Suspect It
A persistent musty smell, visible dark spots inside the unit, or worsening allergy symptoms that improve when away from home are all reasons to have the unit inspected. A combination of professional cleaning and antimicrobial sanitisation addresses existing growth, while fixing any underlying moisture issue, like a slow drain line, prevents it returning.
If this sounds like what's happening with your unit, our AC Sanitisation page covers exactly how we handle it, or you can message us directly for a same-day assessment.
Frequently Asked Questions
Can mould in an AC unit make you sick?
For sensitive individuals, yes — common effects include allergy-like symptoms, respiratory irritation and worsened asthma; healthy individuals may notice milder irritation with prolonged exposure.
How can I tell if my AC has mould without opening it?
A persistent musty smell when the unit runs is the most common early indicator, even before any mould is visually confirmed.
Is it enough to just clean visible mould off the unit?
A visible clean helps, but sanitisation is usually needed to address spores and growth not visible to the eye, especially if the smell persists after cleaning.