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Atopic dermatitis

Atopic dermatitis types

AD

Types of atopic dermatitis

Atopic dermatitis (AD) is a long-lasting inflammatory skin condition that causes recurrent eczema and persistent itching. It develops through a combination of immune dysregulation, genetic susceptibility, environmental influences and changes in the skin barrier.

Modern research shows that AD is not a single, uniform disease. Instead, it includes a range of subtypes with different underlying mechanisms, typical courses and treatment needs. AD can also look different depending on a person’s age, skin type and colour, where on the body it appears, and other health conditions they may have, which can affect both diagnosis and management.

A common clinical distinction is between the extrinsic (allergic) form and the intrinsic (non-allergic) form. This subdivision relies mainly on evidence of sensitization to allergens and personal or family history of other atopic conditions. Understanding these subtypes is useful for patient education, the development of skincare and therapeutic products and decision-making in both clinical and pharmaceutical settings. 

Intrinsic or non-allergic atopic dermatitis

Intrinsic AD is defined by normal IgE levels, an absence of sensitization to common environmental or food allergens and, in many cases, no personal or close family history of asthma, hay fever, or food allergies.

Several clinical and biological features distinguish intrinsic AD:

  • It often appears later in life, although childhood onset can occur.
  • Skin-barrier impairment tends to be less pronounced at the outset. Filaggrin gene mutations and markedly increased transepidermal water loss (TEWL) are less consistently seen.
  • The immune response is more mixed. While type 2 inflammation is still present, other pathways including Th1, Th17 and Th22 are more strongly involved than in the allergic form.
  • Sensitization to non-protein triggers, such as metals or small chemical compounds, may contribute in some cases.

From a treatment and product-development perspective, intrinsic AD often benefits from a stronger emphasis on controlling inflammation and itching.  

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Extrinsic or allergic atopic dermatitis

Extrinsic AD accounts for most cases. It is characterized by raised total IgE levels, sensitization to common allergens such as foods, pollens, house-dust mites or animal dander, and a frequent personal or family history of asthma or allergic rhinitis.

Some of the key features include:

  • More pronounced barrier dysfunction, often reflected in higher TEWL, reduced skin hydration, and a greater likelihood of filaggrin gene mutations.
  • A strong, type 2-driven immune response involving cytokines such as IL-4, IL-13, and IL-5, along with increased eosinophils.
  • Earlier onset in childhood and a higher chance of progressing to other allergic conditions, sometimes described as the “atopic march”.
  • A clearer link between flare-ups and exposure to specific allergens, making avoidance or desensitization strategies more relevant. 

In pharmaceutical and consumer-health contexts, extrinsic AD highlights the need for barrier-repair formulations, allergen-reducing environments, and targeted immunomodulation, including biologic therapy and small-molecule treatments that address type 2 inflammation.

It is important to recognize that intrinsic and extrinsic AD are not completely fixed categories. Some individuals may shift between them over time, and many do not fit neatly into either group. The classification is therefore a theoretical concept rather than a strict rule, best used alongside clinical assessment and emerging biomarker information as personalized approaches to treatment that continues to evolve. 

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