Differentiating between Short 1 cm Hairs by Dermoscopy: Many Possibilities !

How can we tell apart the various causes of short hairs?

I'm frequently asked by patients and physicians how to determine the identify of a short 1 cm or so hair that is seen on the scalp. Looking at the scalp with dermoscopy, one often want to know "Is this a vellus hair I'm seeing or is it an upright regrowing hair as part of a telogen effluvium? ... or is it simply a normal regrowing hair ?"

This chart below helps summarize the main things I think about when I see a short hair. The answer does not necessarily come immediately but rather it comes by asking 4 questions:

1) Is the hair reasonably thick (i.e. 40-50 um or more) or is it very thin (less than 30 um)?

2) Are the ends pointy or blunt?

3) Are these short hairs found all over the scalp or just one area?

4) Are there just a few of these short hairs or lots and lots of them?

By working through these 4 questions, I can generally determine the cause of the short hair I'm seeing on the scalp.