What causes dermatitis?

Causes of Dermatitis

Dermatitis is primarily caused by external agents acting as either irritants (direct chemical damage without immune involvement) or allergens (involving cell-mediated immune responses), with various environmental and genetic factors contributing to its development. 1

Types of Contact Dermatitis

• Irritant Contact Dermatitis (ICD) - Most common form (80% of occupational cases), caused by direct damage to the skin barrier without immune system involvement 2

  • Acute ICD: Results from a single overwhelming exposure or few brief exposures to strong irritants or caustic agents 2
  • Chronic (cumulative) ICD: Develops following repetitive exposure to weaker irritants such as detergents, soaps, organic solvents, and weak acids/alkalis 2
  • Subjective irritancy: Idiosyncratic stinging reactions occurring within minutes of contact, usually on the face, without visible changes - often from cosmetics or sunscreens 3

• Allergic Contact Dermatitis (ACD) - Involves sensitization of the immune system to specific allergens, resulting in T cell-mediated immune response upon re-exposure 1

• Other types:

  • Phototoxic/Photoallergic dermatitis: Triggered by light exposure to certain allergens 1
  • Systemic contact dermatitis: Occurs after systemic administration of a substance to which topical sensitization previously occurred 2
  • Protein contact dermatitis: Results from repetitive handling of proteins (vegetables, meats, fish, etc.) 1

Common Irritants and Triggers

• Soaps and detergents - Damage skin by denaturing stratum corneum proteins and altering intercellular lipids, decreasing water-binding capacity 2

  • Household disinfectants with harsh active ingredients like N-alkyl dimethyl benzyl ammonium chloride 2
  • Antimicrobial soaps containing chlorhexidine, chloroxylenol, or triclosan 2

• Water and environmental factors:

  • Hot water (above 40°C) affects stratum corneum by lipid fluidization 2
  • Frequent hand washing, especially with very hot or cold water 2
  • Low humidity environments 1

• Occupational exposures:

  • Healthcare workers have 30% prevalence of occupational skin disease due to frequent hand washing, gloves, disinfectants, and detergents 2
  • Wet work and exposure to surfactants and detergents 2

• Common allergens:

  • Metals (especially nickel) 1
  • Fragrances and preservatives in personal care products 1
  • Rubber accelerators in gloves 2
  • Topical antibiotics 1

Pathophysiological Mechanisms

• For Irritant Contact Dermatitis:

  • Direct damage to skin barrier through chemical and physical irritants 2
  • Keratinocyte release of proinflammatory cytokines that instigate skin barrier disruption 2
  • Acute loss of surface lipids due to lipid-emulsifying detergents and lipid-dissolving alcohols 2
  • Reduction in moisture in the stratum corneum and stripping of protective lipids 2

• For Allergic Contact Dermatitis:

  • Requires sensitization to a specific allergen, followed by elicitation of inflammatory response upon secondary exposure 2
  • Involves T cell-mediated immune response 1

Risk Factors and Exacerbating Conditions

• Pre-existing atopic dermatitis of the hands 2
• Occlusion (increased duration of glove occlusion without underlying moisturizer) 2
• Application of known allergens (products containing topical antibiotics, adhesive bandages with bacitracin) 2
• Picking at dermatitis-induced scale 2
• Washing hands with dish detergent or other known irritants 2

Clinical Presentation

• Acute phase: Characterized by erythema and vesiculation 2, 1
• Chronic phase: Presents with dryness, lichenification, and fissuring 2, 1
• Affected persons often complain of dryness, burning sensation, and rough skin texture 1

Important Considerations

• Clinical features alone are unreliable in distinguishing between different types of dermatitis, particularly with hand and facial eczema 1, 3
• Patch testing is essential for confirming allergic contact dermatitis when suspected 3
• Multiple factors (endogenous, irritant, and allergic) often coexist in certain eczemas, particularly hand and foot eczema 2