A keratosis is a skin growth caused by a buildup of keratin, the tough protein that forms the outer layer of your skin. Normally, skin cells produce keratin as they mature, rise to the surface, and shed. In a keratosis, that process gets disrupted: either too much keratin is produced, it accumulates faster than it can shed, or it builds up in the wrong place. The result is a thickened, rough, or bumpy patch of skin. There are several distinct types, and they range from completely harmless to potentially pre-cancerous.
How Keratin Buildup Happens
Your skin constantly renews itself. Cells at the base of the outer skin layer divide, fill with keratin as they mature, and eventually reach the surface as flat, dead cells that flake off. This cycle keeps your skin smooth and protective. In a keratosis, the balance tips: cells either multiply too fast, produce excess keratin, or fail to shed properly. Chronic irritation, sun damage, genetics, and infection can all trigger this imbalance.
The specific pattern of keratin buildup determines what type of keratosis forms and whether it poses any health risk.
Seborrheic Keratosis: The Most Common Type
Seborrheic keratoses are the growths people most often notice and worry about. They’re completely benign. These raised, waxy, brown-to-black patches look like they’ve been glued onto the skin, which is why dermatologists describe them as having a “stuck-on” appearance. They can range from a faint, flat spot to a thick, scaly plaque, and they tend to show up on the chest, back, face, and shoulders.
Nearly everyone develops at least a few seborrheic keratoses with age. They tend to multiply over time and can grow to a centimeter or more across. The surface is typically dull and slightly rough, sometimes with visible cracks or tiny pits. They’re not caused by sun exposure and don’t become cancerous. The main reason people have them removed is cosmetic, or because they catch on clothing and become irritated.
One important caveat: some melanomas can mimic the appearance of a seborrheic keratosis. Research published in JAMA Dermatology found that certain features visible under a dermatoscope (the magnifying tool dermatologists use) can make melanomas look deceptively like harmless growths. If a spot changes rapidly, looks uneven in color, or just seems different from your other growths, it’s worth having it examined.
Actinic Keratosis: The Pre-Cancerous One
Actinic keratoses are rough, scaly patches caused by years of sun exposure. Unlike seborrheic keratoses, which are smooth and waxy, actinic keratoses feel like sandpaper. They’re typically small, pink or red, and appear on sun-exposed areas: the face, ears, scalp, forearms, and backs of the hands. A global meta-analysis found an overall prevalence of 14% in the general population, making this an extremely common condition, particularly in fair-skinned adults.
The concern with actinic keratoses is their potential to progress to squamous cell carcinoma, a type of skin cancer. Overall, the four-year risk of an individual treated actinic keratosis becoming invasive cancer is about 3.7%. That number climbs significantly for thicker, more advanced lesions: severe actinic keratoses carry a four-year cancer risk of roughly 21%, and those requiring repeat treatment reach 33.5%. These aren’t alarming odds for any single spot, but most people who develop actinic keratoses have multiple, which adds up.
How Actinic Keratoses Are Treated
Treatment falls into two categories. For individual spots, the most common approach is cryotherapy: a dermatologist sprays liquid nitrogen onto the lesion for 5 to 20 seconds, freezing and destroying the abnormal cells. The area blisters, scabs over, and heals within a few weeks. Curettage (scraping the lesion off) and laser therapy are other options for isolated spots.
When actinic keratoses are scattered across a larger area, dermatologists often use “field therapy” to treat the entire region at once. This includes prescription creams that trigger an immune response or destroy abnormal cells, as well as photodynamic therapy, where a light-sensitive solution is applied to the skin and then activated with a special light. These field treatments cause redness, peeling, and sometimes discomfort for a few weeks, but they address both visible and invisible early lesions across the treated area.
Keratosis Pilaris: The “Chicken Skin” Bumps
Keratosis pilaris is a different condition entirely. It produces tiny, rough bumps where keratin plugs individual hair follicles. The result looks and feels like permanent goosebumps or chicken skin. It most commonly appears on the outer upper arms, thighs, and buttocks, though it can show up on the face and trunk as well.
The condition is genetic, inherited in an autosomal dominant pattern, meaning you only need one copy of the gene variant from one parent to develop it. Researchers have linked it to mutations in the filaggrin gene, which plays a key role in building the skin’s outer barrier. People with eczema or dry skin are more likely to have it, since filaggrin mutations are involved in those conditions too.
Keratosis pilaris is harmless and usually painless, though some people find the texture bothersome. It often improves on its own with age. For those who want to manage it, the goal is softening and dissolving the keratin plugs. Creams containing lactic acid at 5% to 12% concentration can reduce roughness and scaling. One study found that applying 10% lactic acid twice daily for three months led to a 66% improvement in skin roughness, pigmentation, and overall appearance. Urea-based creams at 20% concentration are another well-studied option, effective at breaking down the excess keratin without irritating the skin. Lower concentrations around 10% work for mild cases, while 20% to 30% formulations tackle more stubborn bumps. Consistent daily use matters more than which product you choose, and moisturizing right after bathing helps lock in results.
How to Tell the Types Apart
The three main types of keratosis look and feel quite different from each other:
- Seborrheic keratosis: Waxy, raised, brown to black, smooth surface, looks “stuck on.” Appears anywhere on the body. Painless and benign.
- Actinic keratosis: Flat or slightly raised, rough and sandpapery, pink or skin-colored. Found on sun-exposed areas. Pre-cancerous.
- Keratosis pilaris: Tiny, uniform bumps clustered around hair follicles. Found on upper arms, thighs, buttocks. Genetic and harmless.
The texture difference between actinic and seborrheic keratoses is one of the most reliable visual clues. Seborrheic keratoses have smooth surfaces, while actinic keratoses are rough. Color matters too: a new or changing dark spot, especially one with uneven borders or multiple colors, warrants professional evaluation regardless of which type it resembles. A dermatologist can examine a questionable spot with a dermatoscope and, if needed, perform a biopsy to rule out skin cancer.
Who Gets Keratoses
Almost everyone will develop some form of keratosis during their lifetime. Seborrheic keratoses are nearly universal in older adults and have no known preventable cause. Keratosis pilaris affects up to 40% of adults and is especially common in children and teenagers.
Actinic keratoses are the most preventable type, since they’re driven by cumulative UV exposure. Fair skin, a history of sunburns, living at high altitude or near the equator, and outdoor work all increase risk. They rarely appear before age 40, but in heavily sun-exposed populations, they can show up earlier. Consistent sunscreen use, protective clothing, and avoiding peak sun hours are the most effective ways to reduce your risk of developing them.