July 2025 |  ✓  Medically Reviewed by: Magnus Borres, Director of Medical Affairs

Allergies are immune system reactions to normally harmless substances, such as pollen, chemicals or metals. When an immune response to an allergen triggers a skin irritation, it is referred to as an allergic skin condition.  Skin reactions may manifest with various symptoms, including redness, itching and swelling. Being our body's first defence barrier, the skin is often the first organ to respond to allergens.²

Types of dermatitis: When is it an allergy?

Dermatitis is an inflammation of the skin that can manifest itself in different forms. The main types of dermatitis include:

• Atopic dermatitis (eczema): This is a chronic inflammatory skin disease, often associated with other atopic conditions such as asthma and allergic rhinitis. It is defined as atopic as it is often associated with familiarities and comorbidities linked to a so-called "type 2" inflammation. It affects up to 20% of children and 2-8% of adults worldwide. Atopic dermatitis is characterised by a compromised skin barrier, which allows allergens and irritants to enter. This defect relates to the abnormal production of proteins such as filaggrin, which is essential for maintaining the integrity of the skin.^1,3,9
• Contact dermatitis falls into two categories:
  • Allergic contact dermatitis: (type IV allergic reaction) is caused by an immune reaction to specific allergens, such as metals (e.g. nickel) or plants (for this type of reaction, patch tests are the most utilized tests).^2,9
  • Irritant contact dermatitis: resulting from direct contact with irritating chemicals, without the immune system's involvement. This form is characterized by lesions limited to direct contact with the causative agent. The most frequently involved irritants are detergents, surfactants, emulsifiers, alkalis, acids, oils and solvents.²
• Hives (urticaria): Is characterised by itchy wheals on the skin and may be acute or chronic. Acute hives are often triggered by food or drug allergens, while chronic urticaria may last for months or years without an identifiable cause.^2,8

The diagnosis of skin allergies is based on the scrupulous taking of the patient’s medical history, on clinical observation and specific diagnostic tests. For atopic conditions such as atopic dermatitis, which affects up to 20% of children and between 2% and 8% of adults, the Hanifin and Rajka criteria are still among the most widely-used worldwide.¹ There is, however, no specific biomarker for the diagnosis of these conditions: in the context of eczema the diagnosis is only clinical,  based on the skin involvement distribution and symptoms.^6-8

A common factor is the increase in specific IgE levels in the blood, which may indicate allergic sensitisation. Specific IgE tests are a valuable tool for identifying the allergens potentially involved in skin reactions.^2,6 However, an elevated IgE level does not always correlate with the severity of the symptoms, which is why the diagnosis must always be supplemented with a thorough clinical examination and an analysis of the patient's medical history.⁶

Itching and redness: What are skin allergy symptoms?

Skin allergies can manifest themselves with various symptoms, including:

• Severe itching: often resistant to common antihistamines, since it is mediated by pro-inflammatory cytokines.
• Redness and scaling: typical of atopic dermatitis and contact dermatitis.
• Skin rashes and swelling: may appear immediately or several hours after exposure to the allergen.
• Blisters and crusts: present in some forms of dermatitis, such as eczema.

The difference between eczema and urticaria

Although eczema and urticaria may appear similar, there are key differences:

Characteristics of eczema:

• Causes: it is often associated with genetic, environmental and immunological factors. The impairment of the skin barrier allows allergens to enter.
• Manifestation: it presents as erythematous-desquamative lesions with severe itching. The onset of eczema frequently occurs in the first few months of life and typically within the first year of life.⁷
• Duration: it may be chronic, with flare-ups and periods of remission.

Characteristics of urticaria:

• Causes: it can be triggered by specific allergens or physical factors such as heat or cold.
• Manifestation: characterised by itchy red wheals that may appear rapidly. 
• Duration: usually acute; may clear up in a few hours or days. It is characterized by transient itchy superficial pink or pale skin swellings (weals) that may be accompanied by deeper swellings of the skin, mouth or genital region (angioedema). The swellings come and go quickly without leaving a mark.  Most patients with urticaria improve quickly, but a few will continue to develop episodes of swelling for months or years.⁸

As we have seen, eczema and urticaria are both inflammatory conditions of the skin, but they present significant differences in their causes, clinical manifestations and pathogenetic mechanisms.

Eczema has several aggravating factors and triggers, such as heat, perspiration, emotional stress, and exposure to certain chemicals, cigarette smoke, and cleaning solutions. Additionally, there are common allergens that may cause symptoms, including:⁵

• Animal dander 
• Egg 
• Fish 
• Dust mites 
• Milk
• Peanut
• Pollen 
• Shellfish 
• Soy
• Tree nuts
• Wheat

Eczema is characterised by a defect in the skin barrier; however not all patients with eczema have elevated IgE levels. Therefore, a distinction has been introduced between eczema associated with IgE antibodies (called atopic eczema) and eczema without IgE antibodies (called non-atopic eczema).⁷ Furthermore, the skin microbiome plays a key role in the pathogenesis of eczema, with an abnormal proliferation of pathogens such as Staphylococcus Aureus and Malassezia, which aggravate inflammation and increase susceptibility to skin infections.⁴

Urticaria, on the other hand, is characterised by itchy wheals of variable duration, which can appear and disappear rapidly. Unlike eczema, it is caused by mast cell degranulation, which releases histamine and other inflammatory mediators. Urticaria can be acute or chronic and can have various causes, including IgE-mediated allergic reactions, physical stimuli (heat, cold, pressure) and autoimmune mechanisms.⁷ Urticaria does not involve a structural alteration of the skin, as is the case in eczema, nor is it associated with a skin barrier defect.

Another fundamental distinction concerns the duration of the lesions: in hives, the wheals tend to disappear spontaneously within 24 hours, whereas eczematous lesions persist for a long time and may evolve into skin thickening (lichenification) due to continuous scratching. Moreover, although the itchiness of urticaria responds to antihistamines, that of eczema may not respond sufficiently to these drugs.⁸

These differences are crucial to ensure an accurate diagnosis and suitable treatment.

What is dyshidrotic eczema

Dyshidrotic eczema, also known as acute palmoplantar eczema, is a common type of eczema that presents as blister-like eruptions on the hands and feet. The lesions are extremely itchy and tend to be recurrent.⁴

This type of eczema can be triggered by various factors, including psychophysiological stress, exposure to irritants or environmental allergens.

The treatment of dyshidrotic eczema includes the use of topical therapies to reduce inflammation and relieve itching. It is of paramount importance to avoid scratching the lesions to prevent infectious complications. In some more severe cases, or in those resistant to standard topical treatments, systemic drugs may be prescribed to control the symptoms.⁴