In nature mold and mildew is natural. In homes and other buildings in which people reside, however, mold becomes a problem, since mould can cause severe health damages to people and pets. Therefore, recognizing a mold problem is important.

Sometimes mold is visible and a problem can easily be diagnosed. More often, however, the problem is not visible and is established through other indicators, such as leakages and other water damages. Typical signs of water damage and a potential mold problem are loosening wallpaper or tiles, cracked or peeling paint, cracks, discoloration of walls and darkened, swollen or warped wood. A musty or earthy smell is another way of establishing a mold problem, but not all types of mold emit smells. Often, health problems cause residents to suspect a mold problem.

Mold affects different individuals in different ways, and establishing the cause of a problem can be difficult. Mold causes irritation symptoms (irritated and itching eyes, a cold, a gruff and sore throat, hoarseness, cough, difficulty breathing), airway infections (flu, cold fever, bronchus infection, sinusitis, pneumonia, airway haemorrhage), headaches, tiredness, fever, dizziness and nausea. In children ear inflammations and infection cycles are common.

Mold can be detected if the circumstances needed for mold to grow are known. Mold needs warmth, nourishment and humidity to grow. Room temperatures are optimal for mould growth, although they grow in +4 C-degrees (and survive in minus temperatures). Suitable substrates (nourishment) for mould and mildew are wood, concrete, tile, boards (particle-, dry-, etc), most isolation materials, glad wraps, etc. Most buildings offer the temperature and nourishment that mould needs to grow, and when humidity is also high enough mold problems arise. Mold thrives in spaces where the relative humidity of the air exceeds 70 %, a condition commonly caused by leakage or a construction error.