What is Hair Ice?

Hair Ice or Haareis is a strange winter biological phenomenon. It’s a type of ice only found on fallen branches on the ground. It exudes from the microscopic pores in bare wood, almost as if they had been emitting tiny streams of steam that have snap frozen into fibres of ice. They are very delicate and will melt away in a minute if placed on the palm of your hand!

Dr James Carter of Illinois State University explains it as “Hair Ice is ice that grows outward from the surface of the wood, as super-cooled water emerges from the wood, freezes and adds to the hairs from the base.” It is not frost which results from moisture being deposited onto objects and ten frozen.

It is also now thought that fungi have something to do with it! This was first speculated in 1918, and was certainly my first suspicion on seeing it for the first time. In 2005, researchers Wagner and Mätzler confirmed the link. Pretty much all dead wood contains fungi, often many different species. However, if you kill off the fungi, the hair ice no longer grows. They think that the metabolic activity of fungi inside the dead wood generates carbon dioxide that pushes water to the surface and out of the pores in the wood as rays. This water then freezes and is spun into hair ice. It’s similar to a frosty morning when you exhale and can see your breath. Hair ice seems to be the exhaled frozen breath of fungi!

There is also some organic content in this exuded water causing the hair ice to be slightly sweet and attractive to insects. A sort of insect iced candy floss!

(Wagner, G. & Mätzler, C. (2008) Haareis auf morschem Laubholz als biophysikalisches Phänomen [Hair Ice on Rotten Wood of Broadleaf Trees – a Biophysical Phenomenon]. German, with English abstract.)

The pictures of Hair Ice (Haareis) below were taken in a wood in Central Scotland between Christmas and Hogmanay (28 December 2014).








Since I published this article, further research reported in an article in July 2015 has revealed that the most common fungus linked to the formation of hair ice is Exidiopsis effusa. Full article here: European biologists finally solve mystery of hair ice. EINECS Sci-News, 23 July 2015 throws more light on what causes hair ice.


  1. Very interesting article. I recently found this in my local beech woodland and included my picture in my monthly newsletter. This was picked up by a fungus group who forwarded me your link here. I have my photo available, and a grid reference if you are interested in knowing more?
    Mr N Davies

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