What are upright regrouping hairs and what is the difference between them and miniaturization?

Upright regrowing hairs (URH) refers to a very specific appearance of hairs seen when using an instrument known as a dermatoscope. Upright regrowing hairs are small 0.5 cm to 1 cm hairs and if seen in great numbers in a small unit area are suggestive of a telogen effluvium. If one were to stare at an URH for many months (or somehow place a tiny camera on the scalp and watch it grow), one would see that it not only gets longer but also thicker and thicker in caliber. A miniaturized hair is a thin caliber hair and may or may not grow thicker (depending on the diagnosis). Miniaturized hairs are frequently associated with androgenetic alopecia but can be seen in other conditions. For example, miniaturized hairs can be seen in alopecia areata and traction alopecia. An appearance of miniaturization can also be seen in patients with a massive telogen effluvium where a large number of newly growing thin hairs take in the appearance of miniaturzation.

Hairs vary with different conditions, for example people who are balding often have miniaturization that precedes the balding in those hairs. Exclamation mark hairs are characteristic of alopecia areata, hairs that are damaged from heat or disease, show cracks in the hair shafts under high power examination. Doctor's experienced in the field, often perform microscopic examinations of the hairs with video or hand microscopes