Confluent and reticulated papillomatosis (CARP) is an uncommon skin condition caused by abnormal keratinization, the process by which your skin cells mature and shed. It produces dark, scaly patches that typically appear on the upper trunk and neck, most often in teenagers and young adults. Also known as Gougerot-Carteaud syndrome after the dermatologists who first described it, CARP is frequently mistaken for more common skin conditions, which can delay diagnosis for months or even years.
What CARP Looks Like
The hallmark of CARP is a distinctive pattern of small, dark, slightly raised bumps (papules) that merge together in the center of the affected area and spread outward in a net-like or lace-like pattern at the edges. This is where the name comes from: “confluent” describes the merging center, and “reticulated” describes the web-like periphery. The bumps are usually brown or dull-brown with mild scaling on the surface, and they can flatten into broader patches or plaques over time.
The most common locations are the chest (especially between the breasts), the upper back between the shoulder blades, and the neck. Less frequently, lesions appear on the shoulders, underarms, face, abdomen, elbows, and knees. A hypopigmented (lighter-colored) variant also exists, though it’s rarer. The patches themselves don’t itch or hurt, which is why many people live with them for a while before seeking medical attention. The concern is almost always cosmetic.
Why It’s Often Misdiagnosed
CARP closely resembles two much more common conditions: tinea versicolor (a fungal skin infection) and acanthosis nigricans (dark, velvety patches linked to insulin resistance). Many people with CARP are initially treated with antifungal creams or pills that simply don’t work, because the condition isn’t caused by a fungus. A key clue is that CARP doesn’t respond to antifungal treatment, and a skin scraping examined under a microscope won’t show the yeast typically seen in tinea versicolor.
Compared to acanthosis nigricans, CARP lesions tend to be scalier and more papular rather than smooth and velvety. They also appear in slightly different locations: acanthosis nigricans favors skin folds like the back of the neck and armpits, while CARP centers on the flat surfaces of the upper trunk. Still, the two conditions can overlap in appearance, and some research suggests they may share an association with insulin resistance and metabolic changes.
What Causes It
The exact cause of CARP remains debated. The core problem is disordered keratinization, meaning the skin cells in the affected area don’t mature and turn over normally, leading to a buildup that creates the scaly, raised texture. Several theories attempt to explain why this happens.
One theory points to a bacterial trigger, supported by the fact that antibiotics are the most effective treatment. Another links the condition to hormonal and metabolic factors. Studies have found associations between CARP and obesity, insulin resistance, and type 2 diabetes, particularly in younger patients. Some researchers have proposed that CARP and acanthosis nigricans may sit on a spectrum of skin responses to metabolic dysfunction. There’s also a possible genetic component, as the condition sometimes runs in families, though no specific gene has been identified.
How It’s Diagnosed
There’s no single blood test or lab result that confirms CARP. Diagnosis is primarily clinical, meaning your dermatologist identifies it based on the appearance and distribution of the lesions, your age, and your history of failed antifungal treatment. A skin biopsy can support the diagnosis but isn’t always necessary. Under the microscope, CARP shows thickening of the outermost skin layer (found in about 95% of biopsy samples), along with a wavy or undulating skin surface pattern (about 78% of samples) and mild thickening of the deeper epidermal layers. Importantly, there’s usually little to no inflammation, which helps distinguish it from other conditions.
In adolescents, biopsies tend to show more pronounced surface changes compared to adults, where findings can be subtler and harder to interpret.
Treatment Options
The first-line treatment for CARP is minocycline, a tetracycline-class antibiotic, typically taken twice daily for about six weeks. This clears lesions in most patients, though some need a longer course. The fact that an antibiotic works so well is one reason researchers suspect a bacterial component to the condition, even if no single organism has been definitively blamed.
For people who can’t take minocycline (due to side effects like dizziness, stomach upset, or skin discoloration), azithromycin taken three times per week is an increasingly popular alternative. It has a gentler side effect profile and appears similarly effective. Other options that have shown success include clarithromycin, erythromycin, and certain topical treatments like retinoids, which help normalize the way skin cells turn over.
One frustration with CARP is that it can come back. About 22% of patients in one study experienced a recurrence within six months of finishing treatment. Recurrences can happen months or even years later. Some dermatologists use maintenance therapy, such as a lower-dose antibiotic or a topical retinoid, to keep lesions from returning in patients who relapse frequently.
Who Gets CARP
CARP overwhelmingly affects adolescents and young adults, with most cases diagnosed between the ages of 15 and 30. It occurs across all skin types but is more frequently reported in people with darker skin tones, likely because the pigmentary changes are more visible and more likely to prompt a medical visit. Both men and women are affected, though some case series report a slight female predominance.
If you or your child has been diagnosed with CARP, it may be worth discussing screening for metabolic conditions like insulin resistance, particularly if there are other risk factors such as obesity or a family history of type 2 diabetes. The skin condition itself is benign, but the metabolic associations are worth understanding in the broader context of your health.