Is your home harming you? Asthma, allergies and indoor mould

It is hard to escape indoor mould. It is most commonly found in the wet areas of the home, especially the bathroom and the kitchen, but it can grow anywhere. We all agree that it’s unsightly, but the bigger problem is it can harm your lungs.

According to the findings from our study published recently in the journal Respirology, indoor mould can increase the risk of active asthma, even in those who don’t have an allergy to mould.

The good news is that getting rid of the culprit may reduce the incidence of asthma.

Asthma in middle age

Our research involved the participants in the Tasmanian Longitudinal Health Study, the world’s largest and longest-running population-based study of lung health. This study started in 1968 when 8,583 seven-year-old Tasmanian school-children were enrolled by their parents.

Now in middle age, these original seven-year-olds have been followed at intervals, most recently in 2004-06. At that follow-up, we traced 5,729 participants to determine whether they had asthma or asthma-linked symptoms and the presence of visible mould and other airborne pollutants in their homes. We then allergy tested a subset of 1,383 participants.

When we analysed the data, we found the overall risk of active asthma was increased by 26% in those who had visible mould in the home in the last 12 months.

We also found that the more rooms in the house affected by mould, the greater the risk of active asthma. In other words, there was evidence that the “dose” of mould influenced the risk of active asthma.

These are novel findings, adding to the existing body of knowledge on what might cause asthma.

Identifying the cause

All asthma is not necessarily the same. A lot of asthma is “allergic”, developing in those who test positive to a skin test for a variety of possible allergens. This applies particularly to children and teenagers.

But asthma can also be “non-allergic”, developing in those with negative allergy skin tests. This type of asthma tends to occur more in adults, and interestingly, more often in women than men.

A considerable amount of asthma research has been done with children and adolescents, and in this age group, the risk for allergic asthma associated with mould sensitivity is well known.

But not so well known is that mould exposure can be associated with non-allergic asthma, as our study showed. Our finding that this association was stronger in men than women was a little unexpected, and of considerable interest.

Much of the problem with mould lies with its ability to induce an allergic response in persons genetically predisposed – and mould allergy is common. In our study, 35% of participants reported mould in the home in the last 12 months and 13% of those skin tested had mould allergy. Other studies have found mould allergy in up to 24% of the general population and up to 80% among asthmatics.

One of the problems in trying to decide if mould has a causal role in asthma is that mould allergy often occurs in common with allergies to other asthma-related agents, particularly house dust mites. This co-existence makes it difficult to tease out the role of any single agent.

In addition, mould and dampness go hand in hand, and excessive indoor dampness in its own right is a known risk factor for asthma. Given the potential for climate change to lead to more extreme weather and increase the risk of flooding, indoor dampness may well become more of a problem in the future.

Allergic sensitisation is not the only mechanism by which mould can affect lung health. Mould produces various toxic and chemical substances including mycotoxins, beta-glucans, ergosterol and volatile organic compounds that can have a direct inflammatory effect on the lining of the airways. Such substances don’t depend on inducing an allergic response for their effect on the lungs.

To complicate matters further, how the lungs respond to such agents depends on the “dose” to which an individual is exposed and on the variability in the way different people respond to the same lung stressor.

Reducing the risk

Health authorities suggest that removing mould from the home can make a difference to people susceptible to asthma.

There are several treatments for mould, such as Tea Tree Oil and fermented vinegar solutions. It’s best avoid dry brushes (which can spread mould further) and bleach, which doesn’t kill mould (it merely bleaches the colour so it looks like it has disappeared).

It’s also important to address the causes of mould. This comes down to lessening indoor humidity and dampness by improving home ventilation and heating. This will be more difficult in older houses, which may have ongoing problems with dampness because or broken roof tiles, poor cavity wall ventilation and rising damp.

Finally, all asthma sufferers should routinely use their preventer and reliever medications as prescribed for asthma control and symptom relief.

John Burgess receives funding from NHMRC Australia through the Centre for Research Excellence in Chronic Resplratory Disease.