Auckland Allergy & Eczema Clinic

Mould Allergy

Mould Allergy

What is mould?

Moulds are microscopic fungi which, unlike plants, are unable to produce their own food from sunlight and air. They are made up of clusters of filaments, and live on plant or animal matter, which they decompose for their nourishment. Moulds are among the most widespread living organisms, with many different varieties. The common bread mould is a well known example. Some moulds produce penicillin or other antibiotics, or are necessary for agriculture and food production; other produce potent toxins or are major source for plant disease. Many moulds reproduce by releasing spores into the air, which then settle on organic matter and grow into new mould clusters. These airborne mould spores are far more numerous than pollen grains, and when inhaled can produce allergic symptoms in susceptible individuals.

Where are moulds found?

Moulds can be found in most environments, and unlike pollens do not have a strictly limited season. Their growth is encouraged by warmth and high humidity, however, so they are most prevalent during the humid seasons of the year. Moulds are found out of doors and in the home. They are present in outside air unless there is a cover of snow on the ground, and are especially prevalent in shady, damp areas and on decaying leaves or other vegetation. Mould spores produced outside become widely dispersed through the air, and can enter the home. Other moulds are produced in the home, especially in areas of high humidity such as basements and showers.

Common Allergy Provoking Moulds found in New Zealand

Field (Seasonal)

Alternaria Alternata 

A.Alternata is a common and cosmopolitan species occurring on many plants and other substrates including soils, foodstuffs and textiles. Known habitats are soils, corn silage, rotten wood, composts, bird’s nests, and various forest plants. A. Alternata may cause black spots on tomatoes. It is frequently found on condensed window frames. It is considered an outdoor mould and appears when weather is warm. It’s an important cause for asthma and epidemics of asthma have been reportedly associated with weather changes. There is also a link with sudden deaths for asthma and Alternaria sensitivity

Cladosporium herbarum 

Recordings from all parts of the world show that with a few exceptions, Cladosporium is the most frequent encountered mould in the air. The dry conidia (spores) are carried easily through the air and transported even over oceans. The conidia of Cladosporium can be detected in extremely large numbers e.g more than 35 000 condia/m3 were detected over Leiden (Germany). The indoor counts to a large extent reflect the outdoor concentration. Depending on climatic conditions the conidia may begin to appear in the atmosphere in the spring and rise to a peak in either late summer or early. Cladosporium is one of the most common colonizers of dying and dead plants and also occurs in various soil types, and on food. The mould frequently found in uncleaned refrigerators, foodstuffs, on moist window frames, in houses with poor ventilation, with straw roofs, and situated in low, damp areas. It has been isolated from fuel tanks, face creams, paint and textiles.

Clinical experience 

Cladosporium is one of the moulds most widely studied, which most often produces positive skin test reactions in allergic individuals. In a study of 1300 asthmatic children from Finland, 7.1% had positive (3+) SPT reactions to Cladosporium, being the most common mould allergen causing symptoms in that study.

Storage (Perennial)

Aspergillosis (ABPA)

Is a group of moulds found everywhere worldwide, especially in the autumn and winter in the Northern hemisphere. It grows on cereal grain and is found in barns and also indoors in damp homes, especially the bathroom. Only a few of these moulds can cause illness in humans and animals. Most people are naturally immune and do not develop disease caused by Aspergillus. However when disease does occur it takes several forms.

The types of diseases caused by Aspergillus fumigatus are varied, ranging from an "allergy"-type illness to life-threatening generalised infections. Diseases caused by Aspergillus are called aspergillosis. The severity of aspergillosis is determined by various factors but one of the most important is the state of the immune system of the person.

Allergic Bronchopulmonary Aspergillus

This is a condition that produces an allergy to the spores of the Aspergillus moulds. It is quite common in asthmatics, up to 2% of chronic asthmatics might get ABPA. ABPA is also common in cystic fibrosis patients, as they reach adolescence and adulthood. The symptoms are similar to those of asthma: intermittent episodes of feeling unwell, coughing and wheezing. Some patients cough up brown-coloured plugs of mucus. The diagnosis can be made by X-ray or by sputum, skin and blood tests. In the long term ABPA can lead to permanent lung damage (fibrosis) if left untreated.

The treatment is with steroids by aerosol or mouth (prednisone), especially during attacks. Itraconazole (an oral antifungal drug) is useful in reducing the amount of steroids required in those needing medium or high doses. This is beneficial as steroids have side effects like thinning of the bones (osteoporosis) and skin and weight gain, especially when used for a long time.


Common on spoiled foods and in wine cellars, less allergy provoking than other mould. It is the green "mildew" seen typically in basements.

The storage mould, such as aspergillus and penicillium can grow in areas with lower moisture of 15% or more.

Vapourisers, humidifiers and air conditioners, which have water storage units, can become contaminated with fungi, and become a source of aerosolised mould spores.

Diagnosing Mould Allergy

Specific diagnosis of mould allergy can only be established by a combination of aero biologic studies, positive diagnosis tests (Skin prick test and RAST) and careful recording of symptoms elicited by the causative allergen. Even though positive responses are obtained in diagnosis tests with mould extracts, the clinical relevance of this positivity is often uncertain, because of marked variations in the composition of the mould allergenic extracts.

The airborne exposure unit for most fungi is the spore. In spite of this, most commercial allergen preparations utilize mycelium, often metabolic products and occasionally variable numbers of spores. Several investigators have demonstrated differences in protein and allergen content between spores, mycelium and metabolic products.

Allergen preparations from commercial sources vary widely and among the possible causes for this variability there are:

  • Intrinsic variation between spores and mycelium with respect to antigen content
  • Somatic mutations causing allergen content changes within single cultures
  • Aging and culture variation changes
  • Strain to strain variability
  • Interspecific variability

As a consequence of variable interest and limits connected with frequently poor quality of commercial allergenic extracts, the prevalence of allergic sensitisation to moulds is variable from country to country. It is for this reason why more research in mould allergy is badly needed in New Zealand & the rest of the world. Until then, clinicians could be missing important allergic environmental triggers.

Ways to Reduce Household Mould

Mould will flourish in damp, dark and warm places. Some of the more hardy moulds grow in different, drier situations. The following steps will eliminate the major sources of mould or mildew in your home:

The bathroom

  • Keep it well ventilated and dry. Fitting an extractor fan may be necessary
  • Don’t allow mould to form on the shower recess, shower curtain or walls.

The laundry

  • Allow damp shoes, boots or sneakers to "air out" and dry
  • Don’t allow clothing to remain damp- dry immediately after washing
  • Vent the clothes-dryer to the outside to prevent dampness inside.

The Kitchen

  • Ensure fruit in fruit bowls and all refrigerated food has not gone mouldy. Avoid storing fruit at room temperature for more than 72 hours, especially if completely enclosed in plastic
  • Keep the fridge drip tray clean. Fridges have a collecting ledge which takes inside excess moisture via a pipe to the underside drip-tray. Both the pipe and the drip-tray (out of sight) can become heavily contaminated with mould. Place one teaspoon of White King Bleach down the pipe every two weeks to prevent this from happening

Living areas and bedroom

  • Ensure the drip-tray of air conditioners and evaporative coolers are free of mould.
  • Check any damp walls (especially south facing) for mildew, especially behind wallpaper. Treat with mould inhibitor, then sealer then paint.
  • Avoid indoor plants and none of them should be in a greenhouse setting (humid at 20-25 degrees C). An atrium fernery, open to the inside house, will be a source of mould.
  • Do not allow mattresses to stay damp from bed-wetting. If a foam mattress has been wet in the past then it is likely to contain considerably mould and it should be encased completely in plastic. This applies to pillows that have been allowed to get damp from drippling or mucus.
  • Furniture made of leather or cushions containing foam that has been damp at some time will be prone to contamination with mould. Check for a musty smell.
  • Carpets tend to hold any mould spores that have collected in the house, and they favour growth of some mould, especially if the carpet has been damp at some stage. Removing musty carpet is your best option, not cleaning it.
  • Frequent use of a vapouriser to treat children’s asthma or croup will create dampness which will allow mould to thrive on walls, bedding and furniture. Allow the room to dry out between uses.

Outside the house

  • If the house has a musty smell and evidence of damp, ensure that storm water drainage takes water away from the house, and that guttering is working correctly to stop water running down the outside wall. Look for rising damp in walls- they may need a new damp course. If there is damp beneath the house, clear to allow as much ventilation under the house as possible, and treat mould on under-floorings or bearings
  • Avoid heavy vegetation around and over the house and remove ivy and other climbing plants
  • Keep the yard free of fallen leaves and other garden debris, and ensure the compost heap is well covered and away from harm

What can be done to reduce mould exposure?

Mould sensitive individuals should avoid exposure to areas of high mould growth, such as basements, compost piles, fallen leaves, cut grass, barns and wooden areas. A face mask should be worn when such exposure is unavoidable. In the home, it is important to prevent high levels of humidity. A gauge measuring relative humidity should be obtained, and the level in the house kept below 40%. This can be accomplished by the use of air conditioners and dehumidifiers in the summer, and by preventing over-humidification in the winter. Excess humidity produced by showering or cooking should be removed with an exhaust fan. Mould growing in the home can be killed with various products.