What is keratosis pilaris and what causes it?

Keratosis pilaris occurs when keratin, the structural protein in skin and hair, accumulates inside hair follicles instead of shedding normally, forming a plug that blocks the follicle opening and produces rough, raised bumps. The condition is genetic, often linked to filaggrin gene mutations, and is associated with other atopic conditions like eczema, asthma, and allergic rhinitis.

Why does keratosis pilaris worsen in winter or dry climates?

Low humidity strips moisture from the skin and worsens the underlying keratinization defect, making bumps more prominent. Winter air, indoor heating, and arid climates are the most consistent aggravating factors. The skin inability to retain water creates a cycle where dryness worsens keratinization, which worsens barrier function, which worsens dryness further.

Understanding Keratosis Pilaris Causes

Creator: Superpower
Published: 2026-03-18

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What keratosis pilaris actually is and where it starts

Keratosis pilaris happens when keratin, the structural protein that protects skin, hair, and nails, accumulates inside hair follicles instead of shedding normally. This creates a plug that blocks the follicle opening, producing the characteristic rough, raised bumps. The hair may become trapped beneath the plug, coiling inside the follicle rather than emerging through the skin.

The condition is not inflammatory by default, though it can trigger a mild immune response in some cases, leading to redness around the bumps. The plugs themselves are composed of compacted keratin and dead skin cells. The follicle remains structurally intact, but the keratinization process at the follicle opening is disordered.

The condition tends to run in families and is associated with other atopic conditions like eczema, asthma, and allergic rhinitis. The genetic link is strong: mutations in the filaggrin gene, which encodes a protein critical for skin barrier formation, are found in a significant subset of people with keratosis pilaris. These mutations disrupt the normal maturation and flattening of skin cells, leading to abnormal keratin accumulation at follicle openings.

How keratosis pilaris connects to skin barrier function and immune tone

Keratosis pilaris is not just a surface-level texture issue. It reflects an underlying defect in how the skin barrier forms and maintains itself. Filaggrin is a protein that helps flatten and bind together the outermost skin cells, creating a tight, protective barrier. When filaggrin function is impaired, either through genetic mutations or environmental factors, the skin becomes more permeable, loses moisture more easily, and is more prone to irritation.

This barrier dysfunction explains why keratosis pilaris often coexists with eczema and why both conditions worsen in dry, cold climates. The skin's inability to retain water and protect against external irritants creates a cycle: dryness worsens keratinization, which worsens barrier function, which worsens dryness. The compromised barrier also allows allergens and irritants to penetrate more easily, potentially triggering localized immune responses that contribute to the redness seen in some cases.

What drives flares and severity in keratosis pilaris

Environmental and mechanical triggers

Keratosis pilaris doesn't flare in the same way eczema or psoriasis does, but its severity fluctuates based on environmental and physiological inputs. The most consistent aggravating factor is low humidity. Winter air, indoor heating, and arid climates all strip moisture from the skin, worsening the keratinization defect and making bumps more prominent. Mechanical irritation also plays a role. Tight clothing, friction from repetitive movement, and aggressive physical exfoliation can inflame the follicles and increase redness. Over-cleansing with harsh soaps disrupts the lipid barrier, compounding the problem.

Hormonal influences

Hormonal shifts influence keratosis pilaris as well. The condition often worsens during puberty, when androgen levels rise and sebum production increases. Pregnancy can either improve or worsen symptoms, likely due to fluctuations in estrogen and progesterone, which affect skin cell turnover and barrier function. Some women notice improvement during pregnancy, while others see an increase in bump density and redness.

Dietary and nutritional factors

Diet has been explored as a potential trigger, particularly in individuals with concurrent atopic conditions. High glycemic load and dairy intake have been implicated in worsening inflammatory skin conditions, though the evidence specific to keratosis pilaris is limited. What's clearer is that nutrient deficiencies, particularly in vitamin A, can impair keratinocyte differentiation and worsen follicular plugging. Vitamin A regulates the genes responsible for normal skin cell maturation, and its absence leads to excessive keratin production and abnormal follicle architecture.

Why the same condition looks different and responds differently across individuals

Genetic variation accounts for much of the difference in how keratosis pilaris presents. The specific filaggrin variant a person carries can influence both the severity of keratosis pilaris and the likelihood of developing atopic dermatitis. Some mutations cause complete loss of filaggrin function, while others result in reduced but not absent protein production, leading to milder phenotypes.

Skin type and melanin content also affect presentation. In darker skin tones, the inflammatory response to follicular plugging can trigger melanocyte activation, leading to persistent dark spots even after the bumps resolve. This makes keratosis pilaris on black skin more challenging to treat, as the goal shifts from texture alone to both texture and pigmentation.

Immune phenotype matters too. People with a Th2-skewed immune system, common in atopic individuals, are more likely to experience the red, inflamed variant of keratosis pilaris. Those with a more balanced immune profile may have the non-inflammatory, flesh-colored form. Microbiome composition may also play a role. The skin microbiome in keratosis pilaris has not been extensively studied, but disruptions in the balance of commensal bacteria could theoretically influence follicular inflammation and keratin plug formation.

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When skin symptoms point to something systemic

Keratosis pilaris is usually an isolated finding, but persistent or severe cases warrant a broader look. The condition is strongly associated with atopic dermatitis, and individuals with both conditions often have more severe barrier dysfunction and higher rates of food allergies and asthma. This is part of the "atopic march," the progression from eczema in infancy to asthma and allergic rhinitis in childhood.

Keratosis pilaris can also signal nutritional deficiencies. Severe vitamin A deficiency causes a condition called phrynoderma, which resembles keratosis pilaris but is more widespread and associated with other signs of malnutrition. Deficiencies in essential fatty acids, particularly omega-3s, can impair skin barrier function and worsen follicular keratinization.

In rare cases, keratosis pilaris-like eruptions can be a sign of underlying metabolic or endocrine disorders:

Hypothyroidism slows skin cell turnover and can produce a keratosis pilaris-like texture throughout the body.
Cushing's syndrome affects collagen synthesis and skin integrity, potentially presenting with follicular hyperkeratosis.
Malabsorption syndromes like celiac disease can lead to multiple nutrient deficiencies that manifest as skin changes including follicular keratosis.

What biomarkers can tell you when topicals aren't enough

If keratosis pilaris is severe, treatment-resistant, or accompanied by other symptoms, testing can help identify underlying drivers. Vitamin A levels are worth checking, as deficiency impairs keratinocyte differentiation and can worsen follicular plugging. Vitamin D is also relevant, given its role in immune regulation and skin barrier function.

Thyroid function should be assessed if keratosis pilaris is accompanied by dry skin, fatigue, or other signs of hypothyroidism. A TSH, free T3, and free T4 panel can surface subclinical thyroid dysfunction that may be contributing to skin symptoms.

For individuals with concurrent eczema or a history of atopic disease, testing for food sensitivities or IgE-mediated allergies may be useful. Elevated hs-CRP or other markers of systemic inflammation can indicate that the skin condition is part of a broader inflammatory picture. Tracking ferritin, zinc, and essential fatty acid status can also be informative, as deficiencies in these nutrients impair skin barrier repair and keratinocyte function.

Getting to the root of what's driving your skin

If keratosis pilaris persists despite topical treatment, or if you're dealing with other skin or systemic symptoms, Superpower's 150+ biomarker panel can help you identify the internal factors at play. From thyroid function to vitamin D, ferritin, and inflammatory markers, the panel surfaces the data you need to understand whether your skin is signaling a deeper imbalance. Keratosis pilaris may be common, but that doesn't mean you have to accept it without understanding what's driving it.

Frequently Asked Questions

Filaggrin is a protein that helps flatten and bind together the outermost skin cells to create a tight, protective barrier. When filaggrin is impaired through genetic mutations, the skin becomes more permeable, loses moisture more easily, and is prone to irritation. This barrier dysfunction leads to abnormal keratin accumulation at follicle openings, producing the characteristic bumps of keratosis pilaris.

Keratosis pilaris involves keratin plugs blocking follicles without infection or pustules, while folliculitis is inflammation or infection of the hair follicle caused by bacteria, fungi, or viruses. Folliculitis often presents with a white or yellow pustule at the center of each bump and is frequently itchy. Keratosis pilaris is not infectious and requires keratolytic and barrier-repair approaches rather than antimicrobials.

In darker skin tones, the inflammatory response to follicular plugging can trigger melanocyte activation, leading to persistent dark spots even after bumps resolve. This post-inflammatory hyperpigmentation makes the condition more challenging to treat, as the goal shifts from addressing texture alone to managing both texture and pigmentation simultaneously, often requiring additional targeted treatments.

Severe or treatment-resistant keratosis pilaris warrants testing for vitamin A and vitamin D deficiency, which impair keratinocyte function and immune regulation. Thyroid function (TSH, free T3, free T4) should be assessed if symptoms include dry skin, fatigue, or other hypothyroid signs. Malabsorption conditions like celiac disease cause nutrient deficiencies that can produce follicular keratosis, and hs-CRP can gauge whether the skin changes are part of a broader inflammatory picture.

Treatment focuses on keratolytic acids that dissolve the keratin plug, including alpha-hydroxy acids such as lactic acid and glycolic acid, and urea, which also improves skin hydration. Beta-hydroxy acids like salicylic acid penetrate follicles more effectively. These should be paired with barrier-repair emollients rich in ceramides or fatty acids to address the underlying moisture-retention defect, rather than relying on physical exfoliation alone.