Mould allergy

Moulds can attack nearly all materials and develop especially in damp places. They occur both indoors and outdoors.

Microscope image of mould

Moulds are thread-like micro-fungi. They occur all over the world and grow particularly in places where there is moisture. If living spaces are infested with mould, it must be removed quickly. The greater the infestation, the higher the health risks for those living there.


The most important known allergens among fungi are Aspergillus species, Alternaria alternata, Cladosporium species and Penicillium species, which are all classed as moulds. Moulds are found all over the world, but predominantly in nature, mainly in the soil, in dead organic matter. Spores produced by moulds and released into the air gain access indoors through open windows and doors. They can infest almost any material. Once indoors, moulds develop in places where materials are damp or when the relative air humidity is high. Poorly maintained ventilation systems, air humidifiers or decorative fountains and a lot of plants in a room can also lead to a mould infestation.


Mould allergy, like other respiratory allergies, manifests as allergic runny nose, streaming eyes, cough and shortness of breath and is frequently accompanied by asthma. As well as allergic reactions, moulds also cause irritation of the airways, the mucous membranes of the eyes and the skin. Other non-specific symptoms such as headache or disturbed sleep may also occur. If allergic symptoms occur between July and September, they may be caused by mould and not pollen. One indication for a mould allergy is that the symptoms subside during prolonged periods of fine weather but then increase again after rain. On windy days, mould spores are whipped up by the wind.


Diagnosis is based on a detailed medical history and skin and blood tests. Diagnosis is not straightforward due to the lack of good allergen extracts for allergy testing.


Any fungal infestation in living areas must be removed rapidly and professionally. According to current knowledge, there is no reliable measurement method that can indicate the presence of concealed mould growth indoors. If there is a musty smell or there are indications of previous or current damp problems, a structural engineer should be consulted. It is always important to get rid of the cause, hence eradicate the damp problem. Otherwise, the mould will quickly reappear. People with health problems should not remove even small patches of mould growth.

If symptoms occur despite cleaning, medication such as antihistamines can relieve the symptoms.

Tips and tricks

  • keep relative air humidity to a maximum of 45% and temperature between 20 and 21°C in winter
  • air rooms thoroughly for five to ten minutes twice to three times a day
  • have mould infestation professionally removed
  • find the cause of the increased moisture and eliminate

Facts and figures

It is estimated that about 1–10% of the Swiss population are sensitised to moulds.

Even when the moulds die, the spores survive.

Editors: aha! Swiss Allergy Centre in co-operation with the Scientific Advisory Board. For prevalence figures, see source references.