Keratosis pilaris is primarily genetic. You don’t “catch” it or develop it from something you did wrong. It runs in families and stems from the way your skin produces and processes a protective protein called keratin. About 50% of children and 40% of adults have it to some degree, making it one of the most common skin conditions in the world.
What Happens Inside the Skin
Your skin constantly produces keratin, a tough protein that forms a protective barrier on the surface. In keratosis pilaris, excess keratin accumulates inside individual hair follicles, forming tiny plugs that block the follicle opening. These plugs enlarge the top of the follicle and push up against the skin surface, creating the small, rough bumps you can feel and sometimes see. The plugs often trap one or more coiled or twisted hairs inside, which is why the bumps sometimes look like tiny ingrown hairs.
The surrounding skin may also become mildly inflamed, producing the redness that often accompanies the bumps. Some researchers believe the condition starts not with the keratin itself but with the shape of the hair shaft. Circular hair shafts may rupture the lining of the follicle, triggering inflammation that then leads to the abnormal keratin buildup. Either way, the end result is the same: plugged follicles that create a rough, sandpaper-like texture on the skin.
The Genetic Root
The strongest known genetic link involves a gene called FLG, which provides instructions for making a protein essential to your skin’s outer barrier. When this gene carries certain mutations, the skin barrier doesn’t form properly, leading to drier skin that’s prone to excess keratin production. A Finnish study of over 500 patients found that one specific mutation in this gene made people nearly five times more likely to have keratosis pilaris. Different populations carry different variants of this mutation: two are most common in people of European descent, while other variants are more frequent in Asian populations.
Keratosis pilaris is inherited in an autosomal dominant pattern, meaning you only need to get the gene variant from one parent to develop the condition. If one of your parents has it, there’s a good chance you will too. The same FLG gene mutations are also linked to eczema (atopic dermatitis) and a dry skin condition called ichthyosis vulgaris, which is why these three conditions so frequently overlap. If you have keratosis pilaris, you may also notice unusually prominent lines on your palms, another hallmark of the shared genetic pattern.
Where the Bumps Typically Appear
The upper arms are the most recognizable location, but keratosis pilaris also commonly shows up on the thighs, buttocks, and cheeks. In children, the cheeks are especially common, sometimes giving the face a flushed, rough appearance that gets mistaken for acne or an allergic reaction. The bumps are usually painless and don’t itch, though some people experience mild irritation if they pick at or scrub them aggressively.
Age and Hormonal Patterns
Keratosis pilaris can appear at any age, but it’s most common in young children and peaks during the first decade of life. It frequently becomes more noticeable again during puberty, when hormonal shifts increase keratin production and oil gland activity. For many people, the condition gradually fades on its own by around age 30, though some carry it well into adulthood. The pattern of worsening during adolescence and improving with age is one of the most consistent features of the condition.
Why It Gets Worse in Winter
Cold, dry air pulls moisture from your skin, and keratosis pilaris is fundamentally a condition of impaired skin barrier function. When that barrier dries out further, the keratin plugs become more prominent and the surrounding skin gets rougher and more inflamed. This is why many people notice their bumps are barely visible in summer but flare noticeably between November and March. Indoor heating compounds the problem by further lowering humidity. Running a humidifier during winter months and moisturizing consistently can reduce the seasonal worsening, though it won’t eliminate the underlying condition.
Conditions That Often Accompany It
Because keratosis pilaris shares its genetic roots with other skin barrier disorders, it frequently appears alongside them. Eczema is the most common companion. People with ichthyosis vulgaris, a condition that causes dry, scaly skin, almost always have keratosis pilaris as well. In rarer cases, keratosis pilaris shows up as part of broader genetic syndromes. Children with Noonan syndrome or cardiofaciocutaneous syndrome, both caused by different gene mutations affecting growth and development, have a notably high prevalence of keratosis pilaris.
How Doctors Identify It
Keratosis pilaris is diagnosed visually. No blood tests or biopsies are needed. A doctor looks for clusters of small, rough, follicle-centered bumps in the typical locations. If there’s any doubt, a dermatoscope (a magnifying tool with a light) reveals the telltale signs: thin, short, or coiled hairs trapped beneath a layer of scale, with surrounding redness. The main conditions it can be confused with are folliculitis (infected hair follicles, which tend to be more painful and pus-filled), milia (smooth white cysts that aren’t follicle-based), and acne, which typically involves larger, deeper lesions and affects different areas of the face.
What You Can’t Control and What You Can
You can’t change the genetics that cause keratosis pilaris. No amount of scrubbing, dietary changes, or skincare products will cure it. Despite persistent claims online, there is no strong clinical evidence that vitamin A deficiency causes the condition or that supplementation resolves it.
What you can influence is how visible and rough the bumps appear. Consistent moisturizing, particularly with creams that contain gentle exfoliating ingredients like lactic acid or urea, helps soften the keratin plugs and smooth the skin’s texture. Avoiding hot showers, which strip the skin barrier, and keeping indoor air humidified during dry months both reduce flare intensity. Results from any routine take weeks to become noticeable, and the bumps return when you stop. For many people, the most reassuring thing to know is that the condition is cosmetic, not harmful, and that time itself is often the most effective treatment.