Pathophysiology of Eczema
The pathogenesis of eczema is multifactorial, involving genetic, immune, and environmental factors that disrupt epidermal homeostasis. Two risk factors particularly associated with the development of eczema are a family history of atopy and mutations in the filaggrin (FLG) gene. The FLG gene is critical for the function of the epidermal barrier, and mutations can impair this barrier, allowing allergens, irritants, and bacteria to trigger abnormal immune responses. Increased expression of interleukin-4 (IL-4) and interleukin-13 (IL-13) further promotes a T-helper 2 immune response, leading to compromised skin barrier integrity.

Causes of Eczema
There is no known single cause for eczema. In fact, eczema includes various types, each having at least one contributing factor, sometimes more. Some of the most common causes include a family history of eczema, exposure to certain environmental triggers, and stress.

Overactive Immune System: Atopic dermatitis, the most common type of eczema, is caused by an overactive immune system that leads to a dry and itchy skin barrier. This condition can occur on any part of the body and presents with various symptoms. Most patients exhibit elevated levels of serum Immunoglobulin E (IgE) and often have a personal or familial history of atopy (Type I allergies, allergic rhinitis, and asthma).

Many Factors Contribute to Eczema, Including the Interaction Between Environment and Genetics: When internal or external irritants or allergens "trigger" the immune system, inflammation or flare-ups occur on the surface of the skin. This inflammation is responsible for the common symptoms seen in most types of eczema. Skin folds, particularly in areas like the knees, elbows, backs of the legs, and other areas where skin rubs against skin, can lead to irritation.

Genetics: Eczema also has a potential genetic component, including a protein called "filaggrin" that helps maintain the skin's moisture. A deficiency in filaggrin can lead to dry, itchy skin. If your family members suffer from atopic dermatitis and certain other types of eczema, your risk may be increased.

Environment: In addition to a family history of eczema, many common household items are potential environmental irritants that may provoke allergic reactions, leading to eczema flare-ups.

Common Triggers for Eczema May Include:

• Prolonged exposure to dry air, or extremely hot or cold environments
• Certain types of soaps, shampoos that produce dandruff, bubble bath products, shower gels, and facial cleansers
• Laundry detergents and fabric softeners that contain chemical additives
• Certain fabrics in clothes and bed linens, such as wool or polyester fibers
• Surface cleaners and disinfectants
• Natural liquids, such as juices from fruits, vegetables, and meats
• Fragrances in candles
• Metals in jewelry or utensils, especially nickel
• Formaldehyde, found in household disinfectants, some vaccines, glues, and adhesives
• Isothiazolinone, an antimicrobial agent found in personal care products like baby wipes
• Cocamidopropyl betaine, used as a thickener in shampoos and lotions
• Paraphenylenediamine, used in leather dyes and temporary tattoos
• Dust mites and living in unclean spaces

Stress: Emotional stress can also trigger eczema flare-ups, though the exact mechanisms are not fully understood. Some individuals experience worsening eczema symptoms and flare-ups when they feel "stressed." Others may feel stressed knowing they have eczema, which in turn can exacerbate their skin inflammation.

Complications of Eczema
Infections are the most common complication of eczema, primarily due to the disruption of the epidermal barrier and immune dysregulation caused by mutations in the FLG gene. Secondary bacterial infections are typically caused by Staphylococcus aureus and beta-hemolytic streptococci. Additionally, prolonged scratching can lead to the formation of post-inflammatory scars and lichenification.

Reference:

American Academy of Dermatology Association  https://www.aad.org/public/diseases/eczema/types/atopic-dermatitis

Guidelines for the diagnosis and assessment of eczema https://dermnetnz.org/topics/guidelines-for-the-diagnosis-and-assessment-of-eczema

National Eczema Association https://nationaleczema.org/eczema/

British Association of Dermatologists https://www.bad.org.uk/pils/atopic-eczema/