pathogenesis

Last edited 10/2020 and last reviewed 10/2020

Eczema is a complex condition that is caused by a combination of genetic and environmental influences and is characterised by cutaneous inflammation, immune dysregulation with a T-helper 2 cell-biased response, and epidermal barrier dysfunction

• strongly associated with genetic factors, in particular loss-of function mutations in filaggrin, a key protein involved in formation of the skin barrier, making a primary skin barrier defect the likely primary trigger of eczematous skin inflammation

Possible factors involved in the pathogenesis include:

• genetic - thought to be polygenic or autosomal dominant inheritance with variable penetrance; if both parents have atopic eczema then the likelihood of offspring being affected is approximately 60%.

• diet - may be able to correlate onset and exacerbation to dietary factors such as milk and eggs and the removal of the food item may improve the skin condition.

• environmental factors associated with development and urbinization - migrant studies support that these are important in the aetiology of this condition - at the moment unsure whether these factors are 'allergic' eg new or higher concentrations of airborne or dietary antigens, or whether there are physical factors eg a susceptibility to cutaneous irritation and dryness that is unmasked by cooler, less humid climates. Other environmental factors include hard water, hygiene practices, use of antibiotics early in life (1) and exposure to house dust mites

• exacerbating factors - a wide variety of factors may cause flare-ups of this condition for example:
  • heat, humidity
  • drying out of the skin,
  • contact with wool
    
    
• there is an association between atopic eczema and various congenital conditions e.g. Wiskott-Aldrich syndrome, ataxia telangiectasia, phenylketonuria, Swiss-type agammaglobulinaemia

Reference:

• Flohr C, Mann J. New insights into the epidemiology of childhood atopic dermatitis. Allergy 2014;69(1):3–16
• Sawangjit R et al. Systemic treatments for eczema: a network meta-analysis. Cochrane Database of Systematic Reviews 2020, Issue 9. Art. No.: CD013206. DOI:10.1002/14651858.CD013206.pub2