Confluent and reticulated papillomatosis, often shortened to CARP, is an uncommon skin condition that produces brownish, slightly raised patches typically on the chest, back, and neck. The patches merge together centrally and spread outward in a lace-like or net-like pattern, which is where the name comes from: “confluent” means the spots join together, and “reticulated” means they form a network. Despite its distinctive appearance, CARP is frequently mistaken for more common conditions like tinea versicolor or acanthosis nigricans, and many people cycle through rounds of ineffective antifungal creams before getting the right diagnosis.
What CARP Looks Like
The hallmark of CARP is a cluster of small, flat-topped or slightly raised papules, usually brown or grayish-brown, that coalesce into plaques near the center of the chest or between the shoulder blades. As the patches spread outward from the midline, they become more scattered and take on that characteristic net-like arrangement. The texture is often described as velvety or slightly scaly when you run a finger over it. Most people notice it first on the upper trunk, but it can extend to the neck, shoulders, and upper arms.
Most of the time, CARP does not itch or hurt. It is primarily a cosmetic concern, though its chronic and visible nature can affect quality of life, particularly because the patches tend to darken over time and become more noticeable on lighter skin. On darker skin tones, the presentation can be even trickier: some patients with Fitzpatrick skin types IV and V develop hypopigmented (lighter) rather than hyperpigmented patches, which look almost identical to a common fungal infection called tinea versicolor.1JAMA Dermatology. An Unusual Variant of Confluent and Reticulated Papillomatosis Masquerading as Tinea Versicolor These hypopigmented variants have only rarely been reported and are frequently misdiagnosed, leading to unnecessary antifungal treatment and delayed diagnosis.2PubMed Central. A Case Series of Hypopigmented Confluent and Reticulated Papillomatosis
Who Gets It
CARP tends to show up in adolescents and young adults. A retrospective review of pediatric cases found that patients typically presented with a median age of around 14, with girls outnumbering boys.3PubMed. Retrospective review of confluent and reticulated papillomatosis in pediatric patients A study from southern India looking at a broader age range found a mean age at onset of about 27 years, with a male-to-female ratio of roughly 1 to 1.5.4PubMed Central. Confluent and Reticulate Papillomatosis: A Retrospective Study from southern India The female predominance is consistent across most published series, though CARP occurs in both sexes and across all ethnic groups. It has been reported worldwide, from the United States to Asia, the Middle East, and sub-Saharan Africa. Because it is uncommon, exact prevalence figures are hard to pin down, and the condition is likely underreported given how often it gets mistaken for something else.
Why It Gets Misdiagnosed So Often
If there is one thing that defines the CARP experience for patients, it is the winding road to a correct diagnosis. The condition mimics several far more common skin problems, and doctors who have never seen it may default to a familiar diagnosis.
The most frequent mix-up is with tinea versicolor (also called pityriasis versicolor), a superficial fungal infection caused by Malassezia yeast. Both conditions produce patches on the trunk that can be brown, tan, or lighter than surrounding skin. A potassium hydroxide (KOH) scraping of the skin can sometimes show yeast in CARP patients too, which muddies the picture further. But the critical clue is that antifungal treatment clears the yeast without clearing the patches.5PubMed. Confluent and reticulated papillomatosis (Gougerot-Carteaud) successfully treated with tacalcitol If your “tinea versicolor” keeps coming back despite appropriate antifungal therapy, CARP should be on the table.
The second common look-alike is acanthosis nigricans, the dark, velvety thickening of skin often seen in the neck folds and armpits of people with insulin resistance. Acanthosis nigricans and CARP can actually coexist in the same patient, making differentiation harder.6PubMed Central. Three Cases of Concomitant Acanthosis Nigricans with Confluent and Reticulated Papillomatosis in Obese Patients The key clinical differences are location and texture: acanthosis nigricans favors skin folds like the neck and armpits, while CARP favors the mid-chest and back. Under a microscope, the skin thickening in CARP is milder than what you see in acanthosis nigricans, and the pigment changes differ in how deep they go.7PubMed. Differentiating confluent and reticulated papillomatosis from acanthosis nigricans
Because CARP resembles both of these conditions so closely, it is frequently misdiagnosed and mistreated, sometimes for years.8PubMed Central. Confluent and Reticulated Papillomatosis Resembling Pityriasis Versicolor and Acanthosis Nigricans: Case Report If you have been told you have one of these conditions and treatment is not working, it is worth asking your dermatologist specifically about CARP.
What Causes It
The honest answer is that nobody knows for certain. Several theories have been proposed over the decades, and each has partial support, but none has been proven definitively. The leading candidates include a bacterial trigger, a disordered response to yeast, abnormal skin-cell maturation, insulin resistance, and a genetic predisposition.9PubMed Central. Confluent and reticulated papillomatosis: diagnostic and treatment challenges
The bacterial theory centers on an organism called Dietzia papillomatosis, an Actinomycete bacterium first isolated from the skin of a teenager with CARP.10British Journal of Dermatology. Dietzia strain X: a newly described Actinomycete isolated from confluent and reticulated papillomatosis That bacterium’s name even references the condition. The case for an infectious cause is bolstered by the fact that CARP often responds well to antibiotics, particularly minocycline, which would not be expected if the disease were purely a disorder of skin growth. A review of the literature concluded that if the link between Dietzia species and CARP is confirmed in further studies, treatment decisions should logically follow bacterial sensitivities.11PubMed. Confluent and reticulated papillomatosis: a review of the literature However, Dietzia has not been consistently isolated from all CARP patients, and its broader clinical significance remains narrow.12PubMed Central. Dietzia papillomatosis bacteremia
The keratinization theory takes a different angle. Electron microscopy studies have found unusual structural changes in the skin cells of CARP patients: the outermost layers of skin show abnormal stacking patterns, with increased numbers of melanin-containing granules persisting into the outer layers rather than being shed normally.13PubMed. Confluent and reticulated papillomatosis: clinical, light and electron microscopic studies Earlier microscopic work found transitional cells between deep and surface skin layers that were increased in CARP patients, supporting the idea that the basic problem is abnormal skin-cell differentiation.14PubMed. Confluent and reticulated papillomatosis: a clinical, histopathological, and electron microscopic study The fact that retinoids, which regulate skin-cell turnover, can also clear CARP lends further credibility to this theory.
In reality, multiple factors probably contribute. A person may have an underlying tendency toward abnormal keratinization or insulin resistance that creates a hospitable environment for Dietzia colonization, which then triggers or worsens the visible skin changes. The different theories are not mutually exclusive, and the varied success of very different treatments (antibiotics, retinoids, weight loss) hints that CARP may have more than one pathway to the same endpoint.
The Metabolic Connection
One thread running through many CARP case reports is an association with insulin resistance, obesity, and related metabolic disturbances. Some patients with CARP have concurrent acanthosis nigricans, impaired glucose tolerance, and elevated insulin levels.15PubMed. Confluent and reticulated papillomatosis: a case with concurrent acanthosis nigricans associated with obesity and insulin resistance The proposed mechanism is that high insulin levels may drive skin-cell overgrowth through insulin-like growth factor pathways, essentially pushing skin to thicken and darken in the same way it does in acanthosis nigricans.
A striking recent case report lends further weight to this link. A patient whose CARP had not responded well to standard treatments was started on tirzepatide, a newer weight-loss medication that acts on both GLP-1 and GIP receptors. After losing a modest amount of weight, her CARP cleared significantly. She went on to lose about 18 kilograms over five months of treatment. When the medication was stopped and she regained some weight, the rash partially returned.16PubMed Central. Confluent and reticulated papillomatosis improvement with tirzepatide-associated weight loss: A case report This is a single case, so it is far from proof, but it fits neatly with the theory that metabolic dysfunction and CARP are connected. For patients with CARP who also struggle with insulin resistance or obesity, managing the metabolic issues may help the skin condition indirectly.
A Genetic Component
CARP has been reported in families across multiple generations and in identical twins, which suggests a genetic predisposition that is probably stronger than previously assumed. One report documented CARP running through three generations in two separate families.17PubMed. Familial Confluent and Reticulated Papillomatosis in 2 Kindreds Including 3 Generations A case series involving monozygotic twins concluded that the inheritance component is likely greater than traditionally thought.18International Journal of Dermatology and Venereology. Confluent and Reticulated Papillomatosis in Monozygotic Twins: A Case Series A candidate gene is keratin 16, where loss-of-function mutations have been proposed as one possible contributor to abnormal skin-cell behavior in CARP.19PubMed Central. Confluent and reticulated papillomatosis: diagnostic and treatment challenges
None of this means CARP is purely inherited. It is more likely a condition where a genetic susceptibility interacts with environmental triggers, whether that is bacterial colonization, metabolic changes during puberty, or something else entirely. But if you have been diagnosed with CARP and a first-degree relative develops similar skin changes, it is worth mentioning the family connection to their dermatologist.
How It Is Diagnosed
Diagnosis typically requires a combination of the clinical appearance and a skin biopsy. The biopsy alone is not perfectly specific because the microscopic findings overlap with several other conditions, but it helps rule out alternatives. Under the microscope, the most consistent features are thickening of the outer skin layer (hyperkeratosis), thickening of the middle layers (acanthosis), and gentle undulation of the skin surface (papillomatosis). A study of 40 biopsy specimens found hyperkeratosis in 95%, acanthosis in about 88%, and papillomatosis in about 78% of cases.20PubMed Central. Clinical and Histopathologic Study of Confluent and Reticulated Papillomatosis by Anatomic Site and Age Plugging of hair follicles is another common finding. A separate series of 10 patients in Lebanon found follicular plugging in nine of ten biopsies, and special stains showed yeast forms in more than half.21PubMed. Confluent and reticulated papillomatosis: clinical and histopathological study of 10 cases from Lebanon The presence of yeast does not mean the condition is a fungal infection; it likely reflects the same Malassezia organisms that live on most people’s skin but happen to be more visible in CARP because of the altered skin environment.
Because no single biopsy finding is unique to CARP, dermatologists often rely on a set of diagnostic criteria originally proposed by Davis and colleagues. These require the characteristic clinical appearance, involvement of the upper trunk and neck, a fungal-negative scraping or failure of antifungal treatment, and a response to antibiotics. In practice, many clinicians diagnose CARP when the pattern and location are right and the patient has already failed antifungal therapy.
First-Line Treatment
Minocycline, a tetracycline antibiotic, is the best-studied and most widely used treatment for CARP. It is typically given by mouth for several weeks. In one well-documented case, extended-release minocycline at a weight-based dose produced complete clearance of the skin lesions within eight weeks, with no relapse during follow-up.22PubMed Central. Confluent and Reticulated Papillomatosis Treated with Extended-Release Minocycline The antibiotic may work by targeting Dietzia or other bacteria involved in the condition, or it may work through the anti-inflammatory properties that tetracyclines have independent of their antibacterial effects. Other antibiotics in the same family, like doxycycline, are sometimes substituted depending on cost and tolerability.
For patients who prefer to avoid oral antibiotics or who have contraindications, topical retinoids offer a reasonable alternative. A case report documented complete clearance of CARP lesions after eight weeks of daily application of tretinoin cream at a low concentration. The authors argued that the effectiveness of tretinoin supports the keratinization-disorder theory and suggested that topical retinoids be considered early in treatment when there are no barriers to their use, as they provide a safer alternative to systemic therapy.23PubMed Central. Confluent and Reticulated Papillomatosis Successfully Treated with Topical Vitamin A Derivative
When Standard Treatment Fails
Some patients do not respond to minocycline or doxycycline, or they relapse after stopping. For these refractory cases, oral isotretinoin has emerged as a useful option. One early case report described a teenager whose CARP had resisted numerous previous treatments but cleared with a roughly five-month course of oral isotretinoin and remained in remission afterward.24PubMed Central. Gougerot-Carteaud Syndrome Treated with 13-cis-retinoic Acid A more recent case series described three patients whose CARP was refractory to initial courses of minocycline or doxycycline, all of whom cleared with isotretinoin doses typically used for acne.25Journal of Dermatology Research. Isotretinoin in Refractory Confluent and Reticulated Papillomatosis (CARP): A Case Series Low-dose isotretinoin has also been reported effective in separate cases.26PubMed. Confluent and reticulated papillomatosis: favourable response to low-dose isotretinoin
Isotretinoin carries well-known side effects and requires monitoring, so it is generally reserved for patients who have tried and failed less aggressive options. It is not a casual first-line choice. But for patients stuck in a cycle of partial improvement and relapse, particularly those who also have acne (since isotretinoin treats both), it can be a practical solution. Two female patients with darker skin tones who were treated with low-dose isotretinoin showed reductions in both scaling and pigmentation of their CARP lesions.27Journal of Asia Pacific Aesthetic Sciences. Confluent and Reticulated Papillomatosis: Two Cases in Females of Skin of Color
Relapse and Long-Term Management
One frustrating aspect of CARP is its tendency to come back. Even patients who clear completely on minocycline or retinoids sometimes see patches return weeks to months after stopping treatment. The tirzepatide case mentioned earlier illustrates this pattern well: the patient’s skin cleared as she lost weight, but the rash partially returned within weeks of regaining some of that weight.28PubMed Central. Confluent and reticulated papillomatosis improvement with tirzepatide-associated weight loss: A case report There is no established maintenance regimen, and dermatologists typically handle relapses by repeating whatever worked the first time or escalating to a different agent.
For patients with metabolic risk factors, addressing insulin resistance through weight management, exercise, or medications prescribed for other reasons may help keep CARP in check, though this strategy is based on case-level evidence rather than trials. The condition is not dangerous in a medical sense, but its chronic course and the cosmetic distress it causes mean that many patients want a long-term strategy, not just a single course of treatment.
Living with a Rare Diagnosis
Part of what makes CARP psychologically taxing is the rarity itself. Many patients describe going through multiple rounds of misdiagnosis, being told they simply have a fungal infection that they should be able to clear with over-the-counter creams. By the time a dermatologist recognizes the pattern, there can be years of frustration built up. The visible nature of the patches, often in areas exposed by warm-weather clothing, adds to the burden. Though CARP is sometimes described in the medical literature as “benign” or “asymptomatic,” characterizing it that way dismisses the real impact on self-consciousness and daily life that patients report.
If you suspect you have CARP, asking for a referral to a dermatologist familiar with the condition is the most productive step. A skin biopsy and a failed course of antifungals together provide strong diagnostic evidence. And while the condition can be stubborn, the current treatment toolkit of oral antibiotics, topical retinoids, and, for tougher cases, oral isotretinoin gives most patients a path to meaningful improvement.