Mildew

It appears as a thin, superficial growth consisting of minute hyphae (fungal filaments) produced especially on living plants or organic matter such as wood, paper or leather.

[citation needed] In horticulture, mildews are species of fungus in the order Erysiphales, or fungus-like organisms in the family Peronosporaceae.

In Old English, mildew meant honeydew (a substance secreted by aphids on leaves, formerly thought to distill from the air like dew), and later came to mean mold or fungus.

Molds can thrive on many organic materials, including clothing, leather, paper, and the ceilings, walls and floors of homes or offices with poor moisture control.

Mold growth found on cellulose-based substrates or materials where moisture levels are high (90 per cent or greater) is often Stachybotrys chartarum.

The requirements are a food source (any organic material), sufficient ambient moisture (a relative humidity of 62–93%), and reasonable warmth (77–88 °F or 25–31 °C) is optimal.

Air temperatures at or below 70 °F (21 °C) will inhibit growth, but only if the relative humidity is low enough to prevent water condensation (i.e., the dew point is not reached).

Some energy efficient air conditioners may cool a room so quickly that they do not have an opportunity to also effectively collect and drain significant ambient water vapour.