: What is the difference between eczema and urticaria? What is the difference between eczema and urticaria? I want to know the pathophysiology and most common causes to understand why they are different !

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Eczema (atopic dermatitis)

Atopic dermatitis is a chronic, itchy skin condition that is very
common in children but may occur at any age. It is also known as
eczema and atopic eczema and was formerly known as Besnier prurigo. It
is the most common form of dermatitis.

Pathophysiology

The pathophysiology of atopic dermatitis is complex and
multifactorial, involving elements of barrier dysfunction, alterations
in cell mediated immune responses, IgE mediated hypersensitivity, and
environmental factors. Loss of function mutations in filaggrin have
been implicated in severe atopic dermatitis due to a potential
increase in trans-epidermal water loss, pH alterations, and
dehydration. Other genetic changes have also been identified which may
alter the skin's barrier function, resulting in an atopic dermatitis
phenotype.

The causes of eczema are multifactorial, it relate to a breakdown in the barrier function of the skin, dehydration and an associated immune response and inflammation. For this reason, emollients and topical steroids are commonly used in its management.

Urticaria

Urticaria is characterised by weals (hives) or angioedema (swellings,
in 10%) or both (in 40%). There are several types of urticaria. The
name urticaria is derived from the common European stinging nettle
Urtica dioica.

Pathophysiology

Urticaria is dermal edema resulting from vascular dilatation and
leakage of fluid into the skin in response to molecules released from
mast cells. The major preformed mediator histamine produces a
prototypic, short-lived urticaria. However, the clinical spectrum and
pattern of lesions indicate that other molecules, including
prostaglandins, leukotrienes, cytokines, and chemokines, produced at
different times after mast cell activation contribute to the
polymorphism of this symptom and the variable evolution of this
disease.

The Pathophysiology link goes into some detail about the different forms of urticaria, both immunological (e.g. allergy, infection, vaccination) and non-immunologcial (e.g. aspirin, non-steroidal anti-inflammatory drugs).

The underlying issue is release of inflammatory mediators from mast cells. Histamine is one of the most common of these molecules, which is why antihistamine drugs are an effective treatment for urticaria.

In summary, eczema is localised to the skin, whereas urticaria represents the cutaneous manifestation of a more systemic process.

Sources:

dermnetnz.org

Pathophysiology of Eczema

Pathophysiology of Urticaria