Keratosis Pilaris
Author: Dr Humaira Ahmed
Chief Editor: Dr Daniel Keith
Introduction
NB Keratosis Pilaris is referred to as KP, follicular keratosis, or colloquially as “chicken skin.”
KP is a common benign skin condition characterised by small, rough bumps on the skin’s surface. It results from the abnormal keratinisation of hair follicles, leading to follicular plugging and subsequent inflammation. This condition typically presents as flesh-coloured or slightly red papules, often with a rough texture, mainly on the upper arms, thighs, buttocks, and occasionally on the cheeks.
Important conditions with similar clinical morphology to KP include follicular psoriasis, hypovitaminosis-A associated phrynoderms, perforating folliculitis, pityriasis ruba pilaris, pityriasis ruba pilaris and pityrosporum folliculitis.
Macroscopic Appearance
Fairer skin types (Fitzpatrick 1-3) may show more noticeable contrast between bumps and skin tone. While, darker skin types (Fitzpatrick 4-6) may exhibit more pronounced post-inflammatory hyperpigmentation.
Example in Fitzpatrick Skin Type 2
Example in Fitzpatrick Skin Type 5
Dermoscopic Appearance
Dermoscopically, findings may include:
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Perifollicular erythema and pigmentation
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Twisted/looped hair
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Peripilar white casts
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Vascular ectasias
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Vellus hair
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Grouped hairs
Fitzpatrick Skin Type 2
Fitzpatrick Skin Type 5
Perifollicular erythema and pigmentation:
Perifollicular erythema (yellow arrows) refers to redness or inflammation surrounding the hair follicles, which may be observed on dermoscopy as a reddish hue. This erythema is indicative of underlying inflammation associated with KP.
Twisted/Loop Hair:
Twisted or lopped hairs (blue arrows) are hairs that appear irregularly coiled or bent upon themselves within the affected follicles. While not universally present, the presence of these may suggest a concurrent hair shaft abnormality associated with KP.
Peripilar White Casts:
Peripilar white casts (red arrows) are small, white or yellowish structures encircling the hair shafts within the affected follicles. These casts represent accumulated keratinous material surrounding the hair shafts, contributing to follicular plugging and hyperkeratosis in KP.
Vascular Ectasias:
Vascular ectasias (purple arrows) refer to dilated blood vessels visible under dermoscopy within or around KP lesions. These findings indicate underlying inflammation or vascular remodelling associated with KP.
Vellus Hair:
Vellous hairs (green arrow) are fine, short hairs that are typically present on the body, particularly in areas affected by KP.
Grouped Hair:
Hairs emerging in groups of 2 or 3 (orange arrow) from individual follicles may be observed within KP lesions.
Further reading for this topic: Sonthalia S, Bhatia J, Thomas M. Dermoscopy of keratosis pilaris. Indian Dermatol Online J 2019;10:613-4.