Introduction
Contact dermatitis is an itchy, superficial skin inflammation caused by direct exposure to external agents.
It affects the epidermis and is classified as either irritant contact dermatitis (ICD) or allergic contact dermatitis (ACD).1
Contact dermatitis is the most common occupational skin disease.
Contact dermatitis accounts for 4-7% of consultations with a specialist dermatologist, and the overall prevalence of ACD to a specific allergen is estimated at up to 27%.2
Among cases of contact dermatitis, around 80% are irritant contact dermatitis (ICD).
Aetiology
Contact dermatitis can be irritant (non-immune-mediated) or allergic (immune-mediated).
Formally, contact dermatitis reactions can be classified into the following:3
- Irritant contact dermatitis (acute and chronic)
- Allergic contact dermatitis
- Photoallergic dermatitis
- Phototoxic dermatitis
- Systemic contact dermatitis
- Protein contact dermatitis
In many cases, dermatitis is multifactorial, involving both irritant and allergic mechanisms, often alongside atopic dermatitis. This is especially common in hand and foot dermatitis.4
Irritant contact dermatitis
ICD occurs after exposure to substances that damage the skin barrier. It does not require immune sensitisation.
Following disruption of skin integrity, further irritants penetrate the skin causing inflammation.5
Exposure to milder irritants will normally require chronic exposure to cause ICD, whereas a singular acute exposure to more irritating agents can cause ICD.
Common irritants include:
- Water
- Soap
- Solvents
- Acids or alkalis
- Oxidising/reducing agents
- Metalworking fluids
Allergic contact dermatitis
ACD is a type IV (delayed) hypersensitivity reaction. It requires prior exposure to develop sensitisation.
On re-exposure, T lymphocytes recognise the allergen, triggering inflammation 48-96 hours later.6
Common allergens include:7
- Nickel
- Methylisothiazolinone (preservative in self-care products)
- Fragrances
- Hydroperoxides of linalool (fragrance)
Other common products that contain allergens include cosmetics, acrylic nails and topical antibiotics.
Risk factors
Risk factors for contact dermatitis include:
- Atopic dermatitis
- Occupational exposure to irritants (e.g. healthcare, cleaners, hairdressers)
Clinical features
History
Typical symptoms of contact dermatitis include:
- Itching (more common in ACD)
- Burning or stinging (more common in ICD)
- Erythema
The timeline of symptoms is especially important to ask about when determining the type of contact dermatitis:
- In ICD, symptoms occur minutes to hours after exposure to a strong irritant, or days to weeks after repeated exposure to milder agents
- In ACD, symptoms appear 48-96 hours post-exposure
It is essential to take a detailed exposure history, including work, home, hobbies, and use of cosmetics or cleaning products.
An occupational history is also important; those at most significant risk include cleaners, hairdressers, construction workers, food service workers, healthcare workers, farmers, and beauticians. The use of personal protective equipment should be asked about.Â
Clinical examination
The appearance of contact dermatitis is highly variable but may include:
- Erythema (redness)
- Papules (elevated lesions ≤1cm)
- Oedema (swelling)
- Vesicles (small blister) or bullae (large blister) – more common in ACD but can occur with severe ICD
- Scale (flaking of the skin)
- Hyperkeratosis (thickening of the skin)
- Fissures (cracking in the skin)
Secondary changes may include lichenification (thickened skin with obvious markings) and excoriations (scratch marks).
For suspected ACD, the shape and location of lesions may offer clues:
- Periumbilical dermatitis may suggest nickel allergy from a belt buckle
- Linear dermatitis from plasters may suggest an adhesive allergy
Sentinel sign
The sentinel sign is an early stage of hand ICD in wet work occupations. The sign can be identified when patients have interdigital dermatitis, or dermatitis in the webbed spaces between the fingers.8
However, if a patient presents with only interdigital dermatitis, scabies should be considered.
Differential diagnoses
Differential diagnoses to consider include:
Diagnosis
The diagnosis of contact dermatitis is clinical, based on history and examination.
Further investigations may be needed if there is diagnostic uncertainty or to identify specific allergens.
Investigations
Patch testing
Patch testing is the gold standard for diagnosing ACD. Allergen patches are applied to the skin and assessed at 48 and 72-96 hours.9
The results are graded according to the reaction.Â
Table 1. Patch test grading results
| Grading | Clinical appearance |
|---|---|
| Negative (-) | No reaction |
| Doubtful (?) | Erythema only |
| Weak positive (+) | Palpable erythema, papules |
| Strong reaction (++) | Palpable erythema, vesicles |
| Extreme reaction (+++) | Palpable erythema, bullae |
Repeated open application test (ROAT) may support the diagnosis of suspected allergens. The product is applied twice daily to a small unaffected area of skin (e.g. inner upper arm) for seven days, monitoring for reaction.10 ROAT should not be used for products not intended for use on the skin (e.g. detergents).
Other investigations
If fungal infection is suspected, perform a fungal scraping.
Skin biopsy may be used in rare cases where the diagnosis remains unclear.
Management
The primary aim is to identify and avoid the offending agent. Symptoms usually resolve over time, but chronic cases may persist despite removal of the trigger.
Skin care measures include:
- Soap-free cleansers
- Drying skin thoroughly after washing
- Regular moisturising with emollients, especially of affected areas
- Using lukewarm water for washing
- Limiting unnecessary hand washing and ‘wet work’ (for hand dermatitis)
Topical corticosteroids are the first-line treatment.
In more severe cases, consider topical calcineurin inhibitors or topical PDE4 inhibitors. Systemic immunosuppressants or phototherapy may be needed for refractory cases.
Prevention
As contact dermatitis is often lifelong, patient education is key. Those with ACD should read product labels and be aware of alternative names for allergens.
Gloves and protective measures should be used in at-risk occupations.
Complications
Complications of contact dermatitis may include:
- Secondary bacterial infection, usually with Staphylococcus aureus
- Post-inflammatory pigment changes: hyperpigmentation (especially in darker skin) or hypopigmentation
Reviewer
A/Prof Aaron Boyce
Dermatologist
Clinical Dean of Medicine
University of Adelaide
References
- Pesonen M, Jolanki R, Larese Filon F, Wilkinson M, Kręcisz B, Kieć-Świerczyńska M, Bauer A, Mahler V, John SM, Schnuch A, Uter W; ESSCA network. Patch test results of the European baseline series among patients with occupational contact dermatitis across Europe - analyses of the European Surveillance System on Contact Allergy network, 2002-2010. Contact Dermatitis. 2015. Available from: [LINK]
- Diepgen TL, Ofenloch RF, Bruze M, Bertuccio P, Cazzaniga S, Coenraads PJ, Elsner P, Goncalo M, Svensson Ã…, Naldi L. Prevalence of contact allergy in the general population in different European regions. British Journal of Dermatology. 2016. Available from: [LINK]
- Johnston GA, Exton LS, Mohd Mustapa MF, Slack JA, Coulson IH, English JSC, Bourke JF, McHenry PM, Gibbon K, Buckley DA, Leslie TA, Mallon EC, Wakelin S, Ungureanu S, Hunasehally RYP, Cork M, Natkunarajah J, Worsnop FS, Chiang N, Donnelly J, Saunders C, Brain AG, Exton LS. British Association of Dermatologists’ guidelines for the management of contact dermatitis 2017. British Journal of Dermatology. 2017. Available from: [LINK]
- Oakley A. Contact Dermatitis. DermNet. 2012. Available from: [LINK]
- Ngan V, Patel K, Nixon R. Irritant contact dermatitis. DermNet. 2021. Available from: [LINK]
- Oakley A, Post R. Allergic Contact Dermatitis. DermNet. 2016. Available from: [LINK]
- DeKoven JG, Warshaw EM, Reeder MJ, Atwater AR, Silverberg JI, Belsito DV, Sasseville D, Zug KA, Taylor JS, Pratt MD, Maibach HI, Fowler JF Jr, Adler BL, Houle MC, Mowad CM, Botto N, Yu J, Dunnick CA. North American Contact Dermatitis Group Patch Test Results: 2019-2020. Dermatitis. 2023. Available from: [LINK]
- Schwanitz HJ, Uter W. Interdigital dermatitis: sentinel skin damage in hairdressers. British Journal of Dermatology. 2000. Available from: [LINK]
- Yu J. Contact Dermatitis. BMJ Best Practice. 2023. Available from: [LINK]
- Hannuksela M, Salo H. The repeated open application test (ROAT). Contact Dermatitis. 1986. Available from: [LINK]
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