Allergic Contact Dermatitis (ICD-11: EK00) - Complete Coding and Diagnostic Guide
1. Introduction
Allergic contact dermatitis represents one of the most frequent cutaneous manifestations in dermatological and occupational practice, characterized as an eczematous reaction mediated by specific immunological mechanisms. This condition results from a Type IV delayed-type hypersensitivity response, involving T cells, triggered after exposure to allergenic substances to which the individual was previously sensitized.
The clinical importance of this condition transcends merely dermatological aspects, significantly impacting patients' quality of life, work productivity, and generating substantial costs to health systems. It is estimated that allergic contact dermatitis is responsible for a considerable portion of occupational dermatoses, affecting workers from various sectors such as construction, healthcare services, hairdressers, metallurgists, and cleaning professionals.
Appropriate recognition of this pathology and its correct coding in the ICD-11 system are fundamental for various purposes: establishment of precise epidemiological statistics, identification of occupational patterns, planning of preventive health policies, appropriate resource allocation, and guarantee of labor and social security rights to affected patients.
Precise coding using the code EK00 allows adequate tracking of trends, identification of emerging new allergens, evaluation of the effectiveness of preventive measures, and facilitation of communication among health professionals at different levels of care. The clear distinction between allergic contact dermatitis and other dermatoses, particularly irritant contact dermatitis, is essential for appropriate clinical management and for adequate medical-legal documentation.
2. Correct ICD-11 Code
Code: EK00
Description: Allergic contact dermatitis
Parent category: Skin conditions caused by external factors
Official definition: Allergic contact dermatitis is an eczematous response provoked by a delayed Type IV immunological reaction to a substance or substances to which the individual has been previously sensitized.
This specific code should be used exclusively for confirmed or highly suspected cases of contact dermatitis with proven or presumed allergic mechanism. The ICD-11 classification maintains this condition within the chapter of skin conditions caused by external factors, recognizing its environmental and occupational etiology.
The code EK00 has 13 subcategories that allow additional specification based on the identified causative agent, including metals, cosmetics, topical medications, plants, rubbers, adhesives, and other specific allergens. This hierarchical structure facilitates the identification of epidemiological patterns and allows targeted surveillance of specific allergens.
The definition emphasizes two essential elements: first, the immunological nature of the reaction (Type IV hypersensitivity mediated by T cells); second, the necessity of prior sensitization, distinguishing it from irritative reactions that may occur on first exposure. This pathophysiological distinction has direct implications for clinical management, prognosis, and preventive measures.
3. When to Use This Code
The code EK00 should be applied in specific clinical situations that demonstrate typical characteristics of allergic contact reaction:
Scenario 1: Occupational nickel dermatitis in healthcare professional A nurse develops pruritic eczematous lesions on the hands after three months of work, with specific distribution at sites of contact with metal equipment. Contact testing confirms reactivity to nickel. The clinical presentation includes erythema, vesiculation, scaling, and intense pruritus, with improvement during periods of leave and recurrence upon returning to work.
Scenario 2: Allergic reaction to footwear components A patient presents with chronic bilateral dermatitis on the feet, predominantly on the dorsum, with well-demarcated borders corresponding to contact with the footwear. Investigation through contact testing identifies sensitization to rubber compounds (thiuram or mercaptobenzothiazole). The chronology shows onset after wearing new footwear and persistence with continued use.
Scenario 3: Contact dermatitis from facial cosmetics A woman develops facial dermatitis with erythema, edema, and vesiculation after starting use of a new cosmetic product. The distribution corresponds precisely to the areas of product application. Contact testing reveals positivity for fragrances or preservatives. Discontinuation of the product results in gradual resolution of the condition.
Scenario 4: Sensitization to topical medications A patient undergoing treatment for venous ulcer develops paradoxical worsening with perilesional erythema, intense pruritus, and extension of the affected area. Contact testing identifies allergy to neomycin or another component of the topical treatment used. This scenario exemplifies the importance of considering allergic contact dermatitis in lesions that do not respond to conventional treatment.
Scenario 5: Dermatitis from plants (allergic phytophotodermatitis) A gardener presents with recurrent dermatitis on the hands and forearms, with a characteristic pattern of exposure to specific plants. Contact testing confirms sensitization to sesquiterpene lactones or other plant components. The occupational history and seasonal pattern aid in diagnosis.
Scenario 6: Reaction to adhesives or dressings Development of eczematous dermatitis with geometric shape corresponding exactly to the application area of medical adhesives, adhesive tapes, or dressings. The reaction persists beyond removal of the material and may leave residual hyperpigmentation.
In all these scenarios, essential criteria include: history of exposure to the allergen, latency period compatible with sensitization (except in previously sensitized individuals), eczematous morphology of lesions, topographic distribution correlated to exposure, and ideally confirmation through contact testing.
4. When NOT to Use This Code
The distinction between allergic contact dermatitis and other skin conditions is fundamental for appropriate coding:
Irritant contact dermatitis: When the skin reaction results from direct damage to the epidermal barrier by irritant substances (acids, alkalis, solvents, detergents) without an immunologic mechanism, the appropriate code is different. Irritant dermatitis does not require prior sensitization, can occur on first exposure, typically presents with burning symptoms rather than pruritus, and does not show positivity on allergic contact tests. For these situations, use specific codes for irritant contact dermatitis.
Allergic sensitization without clinical manifestation: When contact testing identifies sensitization to a particular substance, but the patient does not present with active clinical manifestations of dermatitis, the appropriate code is for allergic sensitization by contact without manifest dermatitis. This distinction is important because many individuals may present with positive tests without current clinical relevance.
Atopic dermatitis: Although it may coexist with allergic contact dermatitis, atopic dermatitis has a specific code and distinct pathophysiology. Atopic patients present with genetic predisposition, family history, early onset, characteristic distribution (flexural areas), and elevated serum IgE.
Dyshidrotic eczema: Palmoplantar vesicles without clear relationship to exposure to specific allergens should be coded separately, even though they may eventually coexist with allergic contact dermatitis.
Seborrheic dermatitis: Distribution in seborrheic areas (scalp, face, upper trunk) without relationship to exposure to specific allergens requires distinct coding.
Psoriasis: Despite potentially presenting with lesions on the hands, psoriasis has distinct morphologic characteristics (well-demarcated plaques, silvery scales, Auspitz phenomenon) and is not related to allergenic exposure.
Do not use EK00 for acute urticarial reactions, which represent Type I hypersensitivity, nor for isolated phototoxic or photoallergic reactions, which have specific codes in ICD-11.
5. Step-by-Step Coding Process
Step 1: Assess diagnostic criteria
The diagnosis of allergic contact dermatitis is based on clinical elements, anamnestic information, and when possible, confirmation through specific tests:
Detailed clinical history: Investigate chronology of symptom onset, occupational and domestic exposures, products used (cosmetics, topical medications, metals, rubbers), temporal pattern (improvement during vacations or weekends suggests occupational cause), and history of atopy which may increase susceptibility.
Physical examination: Evaluate lesion morphology (erythema, edema, vesiculation in acute phase; lichenification, fissures and scaling in chronic phase), topographic distribution (correspondence with exposure areas), characteristic patterns (bracelet-shaped, rings, footwear), and presence of distant lesions from autosensitization or hematogenous dissemination.
Contact tests (patch tests): Considered the gold standard for diagnostic confirmation, involves application of standardized allergens to dorsal skin for 48 hours, with subsequent readings. Positive reactions show erythema, infiltration, vesiculation or blisters at the site of the specific allergen.
Relevance criteria: Determine whether test positivity correlates with current clinical presentation, considering actual exposure to the identified allergen.
Step 2: Verify specifiers
After confirming the diagnosis of allergic contact dermatitis, identify available specifiers:
Causative agent: Use EK00 subcategories when the specific allergen is identified (metals, cosmetics, topical medications, plants, rubbers, etc.).
Location: Document affected areas (hands, face, feet, trunk) as this has implications for source identification.
Severity: Classify as mild (minimal erythema and scaling), moderate (erythema, edema, vesiculation) or severe (extensive vesiculation, blisters, erosions).
Duration: Specify whether acute (less than 3 months) or chronic (more than 3 months), as this influences therapeutic approach.
Occupational context: Identify if work-related, as this has social security implications and requires notification.
Step 3: Differentiate from other codes
EH90 - Pressure ulcer: Differs completely from EK00 as it results from tissue ischemia from prolonged pressure, not involving an allergic mechanism. It presents as areas of necrosis on bony prominences in bedridden or mobility-impaired patients.
EH92 - Dermatoses caused by friction or mechanical stress: These conditions result from repetitive mechanical trauma without immunological component. They include calluses, friction blisters and frictional dermatitis. The fundamental difference is the absence of allergic sensitization and direct relationship with physical trauma.
EH93 - Dermatoses due to foreign bodies: Refers to granulomatous or inflammatory reactions caused by the physical presence of foreign material in the skin (tattoos, sutures, fragments), not by Type IV hypersensitivity mechanism to chemical components of these materials.
The essential distinction is that EK00 always involves an immunological mechanism of delayed-type hypersensitivity, requires prior sensitization and presents with eczematous characteristics, while differential codes involve other pathogenic mechanisms.
Step 4: Required documentation
Checklist of mandatory information:
- Detailed description of skin lesions (morphology, distribution, extent)
- Complete chronological history (onset, evolution, aggravating and attenuating factors)
- Relevant occupational and non-occupational exposures
- Products and substances in contact with affected areas
- Contact test results when performed, including allergens tested and reactions observed
- Clinical correlation between positive tests and clinical presentation
- Response to measures avoiding the suspected allergen
- Previous treatments and responses obtained
- Functional and occupational impact of the condition
- Clinical photographs when available
This complete documentation ensures appropriate coding, facilitates continuity of care, provides evidence for medico-legal issues and allows adequate epidemiological analyses.
6. Complete Practical Example
Clinical Case
A 32-year-old hairdresser professional with five years of experience in the profession seeks dermatological care with a complaint of lesions on the hands for approximately six months. She reports an insidious onset of pruritus and erythema on the hands, initially in the interdigital spaces and lateral aspects of the fingers, with progression to the palms and dorsal surfaces of the hands.
The lesions present a recurrent character, with periods of partial improvement followed by exacerbations. The patient notes worsening during the work week and relative improvement on weekends and during a recent two-week vacation. She denies personal or family history of atopy. She reports frequent use of professional hair care products including dyes, bleaches, straighteners, and fixatives.
On physical examination, erythematous plaques with fine scaling are observed, some areas of lichenification, painful fissures on the fingertips and around the nails. There are no active vesicles at the time of examination, but the patient reports having had "small blisters" during more intense flare-ups. The lesions are bilateral and symmetric, predominating in areas of greater contact with chemical products during work.
Given the suspicion of occupational allergic contact dermatitis, patch tests were requested with standard battery and specific battery for hairdressers. After 48 hours of application and subsequent readings at 96 hours, strongly positive reactions (+++) were observed for paraphenylenediamine (PPD), a common component of hair dyes, and moderately positive reaction (++) for ammonium thioglycolate, present in permanent wave and straightening products.
Step-by-Step Coding
Analysis of criteria:
- Confirmed immunological mechanism: Positive patch tests demonstrate Type IV hypersensitivity
- Prior sensitization: Symptoms began after years of exposure, compatible with sensitization process
- Eczematous morphology: Erythema, scaling, lichenification, and history of vesiculation
- Topographic correlation: Distribution on the hands corresponds to areas of greater occupational contact
- Temporal pattern: Improvement with removal from exposure (weekends, vacation)
- Clinical relevance: Identified allergens are routinely used in professional activity
Code selected: EK00 - Allergic contact dermatitis
Specific subcode: A subcategory for allergic contact dermatitis from chemical products used in professional activities may be used, if available in the registration system utilized.
Complete justification:
Coding with EK00 is appropriate because all diagnostic criteria for allergic contact dermatitis are present. Confirmation through patch testing with identification of specific allergens (PPD and ammonium thioglycolate) eliminates diagnostic doubt. The correlation between occupational exposure and clinical manifestations is clear and unequivocal.
This case does not fit irritant contact dermatitis because it presents a latency period (worked five years before symptom onset), positive patch tests confirming allergic mechanism, and morphological characteristics typical of eczema. Atopic dermatitis is ruled out by the absence of personal or family history, onset in adulthood, and clear relationship with occupational exposure.
Complementary codes:
- Additional code for occupational disease, when applicable to the registration system
- Code for specific etiological agent (PPD), if available
- Codes for anatomical location, if required by the system
Documented recommendations:
- Removal from exposure to identified allergens
- Use of personal protective equipment (vinyl or nitrile gloves, not latex)
- Possible need for professional reorientation if protective measures are insufficient
- Topical treatment with corticosteroids and emollients
- Periodic dermatological follow-up
7. Related Codes and Differentiation
Within the Same Category
EH90: Pressure ulcer
When to use: In patients with areas of tissue necrosis resulting from prolonged pressure over bony prominences, typically in bedridden individuals, wheelchair users, or those with severely reduced mobility.
Main difference: Pressure ulcer results from tissue ischemia due to vascular compression, not involving any immunologic or allergic mechanism. It presents as areas of necrosis in progressive stages, from non-blanching erythema to bone exposure, located in pressure-bearing regions (sacrum, heels, trochanters). There is no pruritus, vesiculation, or eczematous characteristics. The pathophysiology is completely distinct from EK00.
EH92: Dermatoses caused by friction or mechanical stress
When to use: For conditions resulting from repetitive mechanical trauma, including friction blisters, calluses, frictional hyperkeratosis, and friction dermatitis.
Main difference: These dermatoses result from direct physical damage to the skin from repetitive mechanical friction, without an immunologic component. They present as skin thickening, formation of serous blisters (not eczematous) or areas of hyperkeratosis at sites of friction (feet in inadequate footwear, hands in manual activities). There is no latency period for sensitization, they do not respond to contact tests, and they do not present the characteristic eczematous morphology of EK00.
EH93: Dermatoses due to foreign bodies
When to use: For cutaneous reactions caused by the physical presence of foreign materials implanted or incorporated into the skin, such as reactions to tattoos, sutures, metal fragments, or other materials.
Main difference: These conditions result from granulomatous or inflammatory reaction to the physical presence of foreign material, not from chemical hypersensitivity to components. They present as nodules, granulomas, or areas of localized inflammation around the implanted material. Although there may occasionally be an allergic component to tattoo pigments or suture materials, when the reaction is primarily to the physical presence of the material, EH93 is used; when there is evidence of an allergic mechanism to specific chemical components, EK00 would be more appropriate.
Differential Diagnoses
Atopic dermatitis: Distinguished by early onset, family history, flexural distribution, elevated IgE, and absence of clear relationship with specific exposures.
Palmoplantar psoriasis: Presents with well-demarcated plaques with silvery scales, no vesiculation, without relationship to allergenic exposures.
Tinea manuum/pedis: Fungal infection confirmed by direct mycologic examination and culture, usually initially unilateral.
Dyshidrotic eczema: Deep palmoplantar vesicles without identifiable cause, may coexist with allergic contact dermatitis.
8. Differences with ICD-10
In ICD-10, allergic contact dermatitis was coded primarily as L23, with subdivisions based on the causative agent (L23.0 for metals, L23.1 for adhesives, L23.2 for cosmetics, etc.).
ICD-11 maintains a similar conceptual structure but offers greater granularity and flexibility in coding. The code EK00 allows more detailed specification of causative agents through its 13 subcategories, facilitating more precise epidemiological surveillance.
Main changes include:
Improved hierarchical structure: ICD-11 organizes contact dermatitis within a more comprehensive category of skin conditions caused by external factors, allowing better understanding of the relationships between different conditions.
Clearer separation: The distinction between allergic contact dermatitis (EK00) and irritant contact dermatitis is more explicit in ICD-11, reducing coding ambiguities.
Multiple coding capability: ICD-11 facilitates the use of multiple codes to simultaneously specify the condition (EK00), the specific causative agent, and the context (occupational, for example).
Practical impact: Health systems that implement ICD-11 obtain more precise epidemiological data, allowing identification of emerging trends, new occupational allergens, and evaluation of the effectiveness of preventive measures. For professionals, more specific coding facilitates medical-legal documentation and communication between specialties.
9. Frequently Asked Questions
1. How is a definitive diagnosis of allergic contact dermatitis made?
The diagnosis is based on a combination of detailed clinical history, physical examination, and ideally, confirmation through contact testing (patch tests). The history should identify potential exposures, symptom chronology, and correlation with activities. The physical examination assesses morphology and distribution of lesions. Contact tests, considered the gold standard, involve application of standardized allergens to the skin for 48 hours, with subsequent readings to identify positive reactions. The clinical relevance of results should always be evaluated by correlating them with the patient's actual exposure.
2. Is treatment available in public health systems?
Yes, treatment for allergic contact dermatitis is generally available in public health systems. The main approach involves identification and avoidance of the causative allergen, the most effective and low-cost measure. Topical treatments with corticosteroids and emollients are essential medications available in most public formularies. More complex cases may require systemic corticosteroids, phototherapy, or immunosuppressants, generally accessible through specialized services. Contact testing may have limited availability in some systems, being performed mainly in dermatology reference centers.
3. How long does treatment last?
Treatment duration varies considerably depending on severity, chronicity, and the possibility of completely avoiding the allergen. Acute cases with complete identification and removal of the allergen may resolve in 2-4 weeks with topical treatment. Chronic cases, especially when complete avoidance is impossible (occupational allergens), may require intermittent or continuous treatment for months or years. The acute phase generally responds to 2-3 weeks of topical corticosteroids, but complete recovery of the skin barrier and resolution of inflammation may take 6-8 weeks. Hydration and skin protection measures should be maintained indefinitely.
4. Can this code be used in medical certificates?
Yes, the code EK00 can and should be used in medical certificates when appropriate. In occupational contexts, precise coding is particularly important as it documents the occupational nature of the condition, supports work absences, justifies modifications in work activities, and substantiates claims for work-related or social security benefits. Documentation should include not only the code, but also a clear description of the condition, identified causative agent, relationship to work activity when applicable, and specific recommendations for absence or modification of exposures.
5. Can allergic contact dermatitis become chronic or permanent?
Yes, allergic contact dermatitis can become chronic, especially when exposure to the allergen persists or is recurrent. Once sensitization is established, it generally persists throughout life, although the intensity of reactions may vary. Repeated exposures can lead to chronic dermatitis with lichenification, fissures, and permanent changes in skin texture. Severe or prolonged cases may result in residual hyperpigmentation or, rarely, scarring. Strict avoidance of the allergen is essential to prevent chronicity.
6. Can I develop an allergy to substances I have used for years without problems?
Yes, absolutely. Allergic sensitization can develop after months or years of exposure without symptoms. This latency period, during which the immune system gradually develops a specific response to the allergen, is characteristic of allergic contact dermatitis. Once sensitized, the individual will present reactions to subsequent exposures, even to minimal amounts of the substance. This phenomenon explains why professionals can work for years without problems before developing occupational dermatitis.
7. Is there a risk of the condition spreading to other parts of the body?
Yes, although allergic contact dermatitis typically manifests at sites of direct contact with the allergen, dissemination can occur through various mechanisms. Autosensitization or "id" reaction can cause eczematous lesions at distant sites. Transfer of the allergen by contaminated hands can lead to lesions in non-directly exposed areas. In severe cases, systemic contact dermatitis can occur if the allergen is absorbed or ingested. Generalized lesions can also result from intense sensitization with widespread exposure.
8. How to differentiate allergic dermatitis from irritant dermatitis in clinical practice?
The differentiation can be challenging but is fundamental. Irritant dermatitis generally occurs on first exposure to strong irritants, causes burning sensation more than itching, presents with less defined borders, and improves rapidly with removal of the irritant. Allergic dermatitis requires prior sensitization, causes intense itching, presents with typical eczematous morphology with vesiculation, and persists days after allergen removal. Contact tests are positive only in allergic dermatitis. In practice, many patients present with mixed components, especially in occupational contexts where exposure to both irritants and allergens occurs simultaneously.
Conclusion
Appropriate coding of allergic contact dermatitis using the EK00 code from ICD-11 requires clear understanding of pathophysiological mechanisms, diagnostic criteria, and differentiation from similar conditions. Precise documentation benefits patients through appropriate treatment, professionals through clear communication, and health systems through reliable epidemiological data for planning and prevention. Recognition of this condition as an important cause of occupational morbidity and its appropriate coding are essential for worker health protection and implementation of effective preventive measures.
External References
This article was prepared based on reliable scientific sources:
- 🌍 WHO ICD-11 - Allergic contact dermatitis
- 🔬 PubMed Research on Allergic contact dermatitis
- 🌍 WHO Health Topics
- 📊 Clinical Evidence: Allergic contact dermatitis
- 📋 Ministry of Health - Brazil
- 📊 Cochrane Systematic Reviews
References verified on 2026-02-04