Keratosis pilaris (KP) — those small, rough, sometimes reddish bumps on the backs of the upper arms, thighs, or cheeks — is a common benign genetic condition where excess keratin plugs the openings of hair follicles.
The core mechanism is follicular hyperkeratinization. Keratinocytes at the follicular opening don't shed properly, forming a hard keratin plug that blocks the hair follicle and creates the characteristic bump. About 40% of adults have some form, with variable severity.
Underlying factors that influence severity:
- Genetics — clearly familial. Autosomal dominant inheritance in many cases.
- Vitamin A metabolism — retinoid signaling regulates keratinocyte differentiation. KP is often reported in people with subclinical vitamin A deficiency, though causation is uncertain.
- Essential fatty acid status — omega-3 status affects keratinocyte differentiation and barrier function.
- Dry environment / low humidity — reliably makes KP worse.
- Overactive keratinization — some hormonal patterns (elevated androgens) worsen it.
What actually helps: gentle exfoliation with lactic acid or urea-containing lotions, adequate omega-3, topical retinoids for stubborn cases. Aggressive scrubbing makes it worse by inflaming the surrounding tissue. Improves in high humidity, worsens in dry winter air.
Blood work that can help identify amplifying factors: vitamin D status, omega-3 index, ferritin.