Hair ice

Hair ice is a rare natural phenomenon and not a fungus or disease.

Also known as:
Ice wool
Frost beard

recognize hair ice
Hair ice, photo: Ronaldhuizer - CC BY 3.0

Hair ice is a rare natural phenomenon and not a fungus or disease phenomenon, although a fungus is involved. Hair ice forms at high humidity and temperatures just below freezing on dead and damp heartwood (inner part of the trunk) of broadleaf trees. That dead wood contains the fungus Exidiopsis effusa, which secretes moisture. The moisture finds its way out through openings in the wood where it freezes in the form of hairs. With high humidity, the released water does not evaporate but freezes as soon as it enters the open air.
Hair ice grows as long as the fungus remains active; as it gets colder, the fungus’s metabolism stops and the production of water ends.
Hair ice is very delicate: when touched it melts and when exposed to the sun it immediately evaporates.
Most likely to find ice hair is early in the morning in shady areas.

Where to find

  • In shaded areas in broadleaf forests and gardens.


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