Unsatisfactory indoor air quality (IAQ) may result from volatile organic compounds (VOCs) and/or particles contaminating the air. Both long- and short-term exposure to VOCs can result in eye, nose, and throat irritation, allergic reactions, headache, fatigue etc (Fiedler et al. 2005). Particles that may carry e.g. microbial compounds such as mycotoxins and endotoxins are also of health concern. Contaminants may leak in from outdoor air, e.g. from industry or traffic. Items brought indoors (furniture, clothes, tools, toys, cleaning agents etc) may contain irritating or harmful chemicals; examples that are particularly worrying are plasticisers (acting as hormone disruptors) and brominated flame retardants. Such substances may adhere to dust particles and contaminate the indoor air. Human activity indoors may also contribute to air contamination (e.g. stirring up dust by walking, cooking, smoking etc); petkeeping leads to more of microbes indoors. Finally, emissions may also spread to the indoor air from the building itself. Such emissions may result from the effect of water on a particular material.