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Contact dermatitis: conducting the allergy investigation
Cosmetics, work, leisure and objects: finding the allergen that is truly responsible
Contact eczema is not always resolved by a simple patch test. Diagnosis often resembles an investigation: where did the lesions begin? When? What actually touches that area? Which products are used at work, at home or during leisure activities? Tests then help confirm or exclude suspects and determine whether a positive result truly explains the eczema.
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3 essential points
1. Contact eczema does not automatically mean allergy
Irritation and allergy may look alike and can coexist. Irritant dermatitis is promoted by water, detergents, solvents, friction or wet work. Allergic contact eczema is a delayed hypersensitivity reaction.
2. A positive patch test does not necessarily identify the culprit
A positive test demonstrates sensitisation. Its clinical relevance still needs to be established: is the allergen actually present in a product that touches the affected area when eczema occurs?
3. The best test begins with a good history
Assessment is a genuine detective investigation: the first site affected, timing, occupation, cosmetics, topical medicines, leisure activities, objects, products brought to the appointment and changes after stopping an exposure.
Exposure and the start of the investigation
How can the allergen reach the skin?
- Direct contact
- Cream on the face, glove on the hand, jewellery or footwear.
- Transferred by hand
- Product on the fingers then transferred to the eyelids or face.
- Airborne
- Dust, sprays, resins, plants or volatile substances.
- Via an object
- Telephone, tool, spectacles, clothing, handle or device.
- Consort contact
- Product used by someone close to you then transferred by contact.
- Systemic route
- More rarely, internal exposure to a substance in a person who is already sensitised.
| Route of exposure | Example |
|---|---|
| Direct contact | Cream on the face, glove on the hand, jewellery or footwear. |
| Transferred by hand | Product on the fingers then transferred to the eyelids or face. |
| Airborne | Dust, sprays, resins, plants or volatile substances. |
| Via an object | Telephone, tool, spectacles, clothing, handle or device. |
| Consort contact | Product used by someone close to you then transferred by contact. |
| Systemic route | More rarely, internal exposure to a substance in a person who is already sensitised. |
Starting the ‘detective interview’
First question: where did the very first patch appear? Then: on what date, suddenly or gradually, during which activity, with which new product, treatment change or leisure activity?
This timeline is often more informative than the current location because longstanding eczema may spread and lose its initial pattern.
The history: reviewing every exposure
- Occupation
- Actual tasks, products handled, gloves, washing, dust, resins, glues, paints and disinfectants.
- Cosmetics
- Creams, make-up, perfume, shampoo, hair dye, sunscreen, nail varnish/gel, ‘organic’, natural or homemade products.
- Treatments applied
- Topical corticosteroids, antiseptics, eye drops, ointments, dressings and medical devices.
- Leisure activities
- DIY, resin, gardening, mechanics, painting, pottery, music, sport and sewing.
- Clothing/accessories
- Jewellery, watches, shoes, belts, textiles and protective equipment.
- People close to you
- Products used by a partner or child that may indirectly touch you.
| Area | Questions to ask |
|---|---|
| Occupation | Actual tasks, products handled, gloves, washing, dust, resins, glues, paints and disinfectants. |
| Cosmetics | Creams, make-up, perfume, shampoo, hair dye, sunscreen, nail varnish/gel, ‘organic’, natural or homemade products. |
| Treatments applied | Topical corticosteroids, antiseptics, eye drops, ointments, dressings and medical devices. |
| Leisure activities | DIY, resin, gardening, mechanics, painting, pottery, music, sport and sewing. |
| Clothing/accessories | Jewellery, watches, shoes, belts, textiles and protective equipment. |
| People close to you | Products used by a partner or child that may indirectly touch you. |
Location provides clues, not the diagnosis
- Eyelids
- Cosmetics, eye drops, perfumes, hand-transferred nail products/acrylates and airborne allergens.
- Face/neck
- Cosmetics, perfumes, hair dye, preservatives and airborne exposure.
- Hands
- Occupation, wet work, gloves, household products, metals, resins and food.
- Feet
- Footwear, rubber, glues, leather/chromium and textiles.
- Armpits
- Deodorants, perfumes and preservatives.
- Lips
- Cosmetics, toothpastes, topical medicines and objects/instruments.
- Anogenital area
- Hygiene products, wipes, topical medicines, preservatives and perfumes.
- Exposed areas
- Consider airborne exposure or photoallergy.
| Area | Clues to investigate |
|---|---|
| Eyelids | Cosmetics, eye drops, perfumes, hand-transferred nail products/acrylates and airborne allergens. |
| Face/neck | Cosmetics, perfumes, hair dye, preservatives and airborne exposure. |
| Hands | Occupation, wet work, gloves, household products, metals, resins and food. |
| Feet | Footwear, rubber, glues, leather/chromium and textiles. |
| Armpits | Deodorants, perfumes and preservatives. |
| Lips | Cosmetics, toothpastes, topical medicines and objects/instruments. |
| Anogenital area | Hygiene products, wipes, topical medicines, preservatives and perfumes. |
| Exposed areas | Consider airborne exposure or photoallergy. |
When should allergy assessment be offered?
- Chronic, recurrent or treatment-resistant eczema despite appropriate care.
- Involvement of the hands, face or eyelids, lips, feet, armpits or anogenital area, or widespread involvement.
- An unexplained change in eczema distribution or involvement of sun-exposed areas.
- Suspected cosmetic, device, topical medicine, personal product or occupational product.
- Suspected occupational cause: improvement at weekends or on holiday and relapse after returning to work.
Individually selected allergens and tests
Main contact-allergen families
- Metals
- Nickel, cobalt and chromium.
- Fragrances
- Fragrances, Myroxylon/balsam of Peru and oxidised terpenes.
- Preservatives
- MI/MCI, benzisothiazolinone, formaldehyde and formaldehyde releasers.
- Rubber
- Thiurams, carbamates, mercaptobenzothiazoles and other accelerators.
- Hair dyes
- PPD and related molecules.
- Acrylates/methacrylates
- Artificial nails, glues, dental materials and medical devices.
- Resins/glues
- Epoxy, colophony and adhesive resins.
- Topical medicines
- Some antibiotics, anaesthetics and corticosteroids.
- Plants/cosmetics
- Propolis, sesquiterpene lactones, some glucosides and other allergens depending on the products.
| Family | Examples/common sources |
|---|---|
| Metals | Nickel, cobalt and chromium. |
| Fragrances | Fragrances, Myroxylon/balsam of Peru and oxidised terpenes. |
| Preservatives | MI/MCI, benzisothiazolinone, formaldehyde and formaldehyde releasers. |
| Rubber | Thiurams, carbamates, mercaptobenzothiazoles and other accelerators. |
| Hair dyes | PPD and related molecules. |
| Acrylates/methacrylates | Artificial nails, glues, dental materials and medical devices. |
| Resins/glues | Epoxy, colophony and adhesive resins. |
| Topical medicines | Some antibiotics, anaesthetics and corticosteroids. |
| Plants/cosmetics | Propolis, sesquiterpene lactones, some glucosides and other allergens depending on the products. |
What is tested?
The European baseline series (EBS) tests for common allergens and may reveal unsuspected sensitisation. It is supplemented according to the site, occupation, leisure activities and products actually used.
- Patch tests
- Investigate delayed hypersensitivity. The baseline series is often supplemented with specialist series and the patient’s own products.
- Photopatch tests
- When a reaction appears to be triggered or worsened by light.
- Semi-open test
- For some products that may be irritant under occlusion.
- ROAT
- Clarify whether a product is responsible or tolerated through repeated applications under medical instructions.
- GRAT
- When a glove remains suspect despite conventional assessment.
- Use test
- Controlled reintroduction of a finished product under conditions close to normal use.
- Prick/prick-to-prick test
- For an immediate reaction or suspected protein contact dermatitis.
| Test | Why? |
|---|---|
| Patch tests | Investigate delayed hypersensitivity. The baseline series is often supplemented with specialist series and the patient’s own products. |
| Photopatch tests | When a reaction appears to be triggered or worsened by light. |
| Semi-open test | For some products that may be irritant under occlusion. |
| ROAT | Clarify whether a product is responsible or tolerated through repeated applications under medical instructions. |
| GRAT | When a glove remains suspect despite conventional assessment. |
| Use test | Controlled reintroduction of a finished product under conditions close to normal use. |
| Prick/prick-to-prick test | For an immediate reaction or suspected protein contact dermatitis. |
Safety: do not test products yourself
Corrosive or industrial products, products of unknown composition and highly sensitising products may cause irritation or active sensitisation. Acrylates in particular must not be used in an improvised ROAT.
ROAT, GRAT and use tests: what are they for?
- ROAT
- A product remains strongly suspected despite a negative patch test, or the relevance of a positive result needs clarification.
- GRAT
- Assess a glove worn in real conditions when it remains suspect in hand eczema.
- Use test
- Check whether a finished product triggers symptoms under conditions close to real life, when considered sufficiently safe.
| Test | What it helps clarify |
|---|---|
| ROAT | A product remains strongly suspected despite a negative patch test, or the relevance of a positive result needs clarification. |
| GRAT | Assess a glove worn in real conditions when it remains suspect in hand eczema. |
| Use test | Check whether a finished product triggers symptoms under conditions close to real life, when considered sufficiently safe. |
A positive result: the investigation is not over
When should an occupational cause be suspected?
The Mathias criteria provide a simple framework. Several positive answers strongly support the plausibility of occupational dermatitis:
- Is the appearance compatible with contact dermatitis?
- Are plausible irritants or allergens present at work?
- Does the anatomical distribution match occupational tasks?
- Is the timeline compatible with work?
- Has a non-occupational cause been considered?
- Does stopping exposure improve the eczema?
- Do tests or other investigations support the link?
Important clue
Improvement during holidays plus relapse after returning to work is a strong occupational clue, but is not sufficient proof on its own.
Allergens to consider by occupation
- Hairdressing
- PPD/dyes, persulfates, thioglycolates, preservatives and rubber accelerators.
- Healthcare
- Glove accelerators, disinfectants, glutaraldehyde, adhesives and topical medicines.
- Dentists/dental technicians
- Acrylates/methacrylates, gloves and resins.
- Nail/beauty work
- HEMA and other (meth)acrylates, glues/cyanoacrylates.
- Construction/painting
- Chromates, cobalt, epoxy, isothiazolinones, resins and rubber.
- Mechanics/metalworking
- Metals, metalworking fluids/preservatives, epoxy resins and rubber.
- Cleaning
- Often irritation/wet work; also gloves, biocides, perfumes and preservatives.
- Food trades
- Irritation and gloves; consider protein contact dermatitis, which is investigated with immediate tests.
- Agriculture/floristry
- Plants, sesquiterpene lactones, rubber and occupational products.
- Footwear/textiles
- Chromium, dyes, glues/resins and rubber.
| Occupation/exposure | Allergens or mechanisms to consider |
|---|---|
| Hairdressing | PPD/dyes, persulfates, thioglycolates, preservatives and rubber accelerators. |
| Healthcare | Glove accelerators, disinfectants, glutaraldehyde, adhesives and topical medicines. |
| Dentists/dental technicians | Acrylates/methacrylates, gloves and resins. |
| Nail/beauty work | HEMA and other (meth)acrylates, glues/cyanoacrylates. |
| Construction/painting | Chromates, cobalt, epoxy, isothiazolinones, resins and rubber. |
| Mechanics/metalworking | Metals, metalworking fluids/preservatives, epoxy resins and rubber. |
| Cleaning | Often irritation/wet work; also gloves, biocides, perfumes and preservatives. |
| Food trades | Irritation and gloves; consider protein contact dermatitis, which is investigated with immediate tests. |
| Agriculture/floristry | Plants, sesquiterpene lactones, rubber and occupational products. |
| Footwear/textiles | Chromium, dyes, glues/resins and rubber. |
After testing: what the patient should understand
Exact allergen name · synonyms · common sources · possible cross-reactions · reading INCI lists · finding a substance in a safety data sheet · products to avoid · possible alternatives · suitable protective measures.
A written report and targeted avoidance advice are essential. For occupational exposure, the allergist/dermatologist and occupational physician must link the positive test to actual exposure before any major decision.
Common misconceptions
- ‘My patch test is positive: I have found the cause.’
- Not necessarily. Clinical relevance must be established.
- ‘My patch tests are negative: my eczema is not contact-related.’
- False: irritation, an allergen that was not tested or another mechanism remain possible.
- ‘I apply nothing to my eyelids, so my products cannot be responsible.’
- False: hand-transferred or airborne contact is possible.
- ‘Organic/natural means hypoallergenic.’
- False.
- ‘A product used for ten years cannot sensitise me.’
- False: sensitisation can develop after repeated exposure.
- ‘Every occupational hand dermatitis is an allergy.’
- No: irritant dermatitis is very common.
- ‘I can test my product myself on my arm.’
- No: some products may cause dangerous irritation or sensitisation.
| Misconception | SOS Allergo guidance |
|---|---|
| ‘My patch test is positive: I have found the cause.’ | Not necessarily. Clinical relevance must be established. |
| ‘My patch tests are negative: my eczema is not contact-related.’ | False: irritation, an allergen that was not tested or another mechanism remain possible. |
| ‘I apply nothing to my eyelids, so my products cannot be responsible.’ | False: hand-transferred or airborne contact is possible. |
| ‘Organic/natural means hypoallergenic.’ | False. |
| ‘A product used for ten years cannot sensitise me.’ | False: sensitisation can develop after repeated exposure. |
| ‘Every occupational hand dermatitis is an allergy.’ | No: irritant dermatitis is very common. |
| ‘I can test my product myself on my arm.’ | No: some products may cause dangerous irritation or sensitisation. |
Before my appointment: the detective kit
Photographs of lesions at the start of a flare · list of daily products · cosmetics · medicines applied · packaging/ingredients · glove references · occupational products · safety data sheets · leisure/DIY activities · changes during holidays · previous patch-test results.
Final message
Finding the allergen responsible for contact eczema often resembles an investigation more than a simple series of patch tests. The right diagnosis combines timing, location, actual exposure and individually selected tests. Identifying the true culprit enables targeted avoidance without unnecessarily removing dozens of products.
You may also want to read
More to read on SOS Allergo
Patch tests: preparation and procedure · ROAT, GRAT and use tests · Eczema and contact dermatitis · Hairdressing: occupational allergies · Bakery: occupational allergies · Laboratory tests in allergy · Latex and latex-fruit syndrome
Main references
- European Society of Contact Dermatitis. Guideline for Diagnostic Patch Testing - Recommendations on Best Practice. Update 2026.
- Wilkinson M, et al. The European baseline series and recommended additions: 2023. Contact Dermatitis. 2023.
- Uter W, et al. European Surveillance System on Contact Allergies (ESSCA): European baseline series results 2021-2022.
- Mathias CG. Contact dermatitis and worker’s compensation: criteria for establishing occupational causation and aggravation. J Am Acad Dermatol. 1989;20:842-848.
- Chu C, Marks JG Jr, Flamm A. Occupational Contact Dermatitis: Common Occupational Allergens. Dermatol Clin. 2020;38:339-349.
- Hollins LC, Flamm A. Occupational Contact Dermatitis: Evaluation and Management Considerations. Dermatol Clin. 2020;38:329-338.
- Lamouroux C, et al. Glove-related contact dermatitis: Diagnostic value of a repeated application test. Contact Dermatitis. 2024;90:528-530.
- GERDA. Règles de bonnes pratiques des tests épicutanés. 2023.
This information sheet does not replace a specialist consultation. The products to test, their preparation and the test procedures must be decided by the medical team.
Scientific review: September 2026 · sosallergo.fr
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