30th July 2026

Contact Dermatitis

Allergic Contact Dermatitis 

Background

Contact dermatitis also known as contact eczema, is an exogenous inflammatory skin disorder. The two main subtypes of the condition are Irritant contact dermatitis (ICD) and allergic contact dermatitis (ACD). ACD is a T-cell mediated type 4 hypersensitivity reaction triggered by exposure to an allergen hosts are previously sensitised to. It is a relatively common disease 

Epidemiological data on ACD is sparse and thus the incidence and prevalence is not known.

Aetiology

Allergens act as haptens (small hydrophobic chemicals) and bind to form a hapten-protien complex to become antigenic and penetrate the stratum corneum. The complex in engulfed by langarhans cells which migrate to lymph nodes, and present the antigen to naive CD4 T cells that proliferate into memory and effector T cells, causing sensitisation to the allergen. Re-exposure will lead to an inflammatory reaction after approximately 48-72 hours, presenting as a dermatitis. 

Risk factors

• Occupation: e.g. hairdressing, construction, chemical industry, healthcare professionals 
• Age: sensitisation occurs early in childhood
• History of atopy

Common allergens include: nickel, neomycin, myroxylon pereira, fragrance mx, thimerosal, sodium gold thiosulfate. Poison ivy is also a common cause. 

Clinical manifestations

Acute ACD

• Initially confined to site of contact, but diffuse reactions may occur
• Erythematous lesion
• Itch is the predominant symptom
• Burning in some cases 
• Oedema
• Blistering

Chronic ACD

• Dry, thick scale
• Hyperkeratosis
• Lichenification
• Fissures (cracking)

Differential diagnosis 

• Irritant contact dermatitis
• Atopic dermatitis
• Palmoplantar psoriasis 
• Contact urticaria
• Fungal infections e.g. Tinea corporis 

Investigations

Patch testing: help differentiate between ACD and ICD

Medical management 

• Identification of trigger
• Avoidance of future exposure
  • Education
  • Minimise contact with allergen
  • Use of gloves
• Treatment of existing dermatitis 
  • Emollients: reduce transepidermal water loss and restore the skin barrier
  • Topical corticosteroids
  • Topical/oral antibiotics for secondary infection
  • Phototherapy/photochemotherapy
  • Calcineurin inhibitors 
  • Systemic immunosuppressants e.g. azathioprine 

Complications

• Disseminated secondary eczema
• Lichenification
• Secondary bacterial infection

Irritant Contact Dermatitis

Background

Contact dermatitis also known as contact eczema, is an exogenous inflammatory skin disorder. The two main subtypes of the condition are irritant contact dermatitis (ICD) and allergic contact dermatitis (ACD). Irritant contact dermatitis is a skin reaction that occurs upon exposure to environmental substances or factors which damage the skin barrier. Mainstay treatment involves avoidance of the irritant and emollients to maintain the skin barrier function. Prognosis is good if the irritant is avoided with restoration of healthy skin in 4 weeks. 

Epidemiology 

ICD accounts for approximately 80% of occupation related contact dermatitis and is the more common subtype. Prevalence of ICD ranges between 0.4 to 4% of the population, however this is likely an underestimate as a large proportion of patients do not seek medical attention. The condition has a female predominance. 

Aetiology

The exact pathogenesis of the condition is unknown, however there appears to be disruption of the epidermal layer by the irritant which leads to increased skin permeability and transepidermal water loss allowing the chemical/irritant to penetrate. Keratinocyte injury with cytokine release e.g. interleukin 1-alpha, interleukin-1-beta, IL-6 and TNF-alpha triggers an inflammatory response. 

Risk factors

• Young age
• Female
• Atopy

Common irritants

Table 6: Common irritants in ICD

Environmental factors such as temperature and humidity can also have an impact. 

Clinical manifestation

Areas commonly affected are the face, dorsum of the hands and finger webs due to relatively thinner stratum corneum. 

Acute ICD: singular exposure to the offending agent

• Burning/pain
• Localised erythema (redness) 
• Vesicles (blistering)
• Oedema (swelling)

Chronic ICD: multiple exposures to irritant

• Erythema (redness)
• Scale
• Lichenification
• Hyperkeratosis
• Fissures (cracking of the skin)

Diagnosis is largely clinical, based on a history of exposure to the irritant followed by the development of dermatitis.

Investigations

• Patch testing: help differentiate between ICD and ACD
• Histological examination: useful to differentiate from other inflammatory dermatoses

Differential diagnosis

• Allergic contact dermatitis
• Atopic dermatitis
• Psoriasis
• Tinea 
• Scabies 

Medical/surgical management 

• Identification of trigger
• Avoidance of future exposure
  • Minimise contact with irritants
  • Use of gloves
  • Lukewarm water
  • Small amounts of soap-free skin cleansers
  • Drying hands thoroughly
• Treatment of existing dermatitis 
  • Emollients: reduce transepidermal water loss and restore the skin barrier
  • Topical corticosteroids
  • Calcineurin inhibitors 
  • Phototherapy 

Complications  

• Disseminated secondary eczema
• Lichenification
• Secondary bacterial infection