Eczema versus Psoriasis: What are the similarities and differences?

Similar causes.

Theatopic eczema is promoted by agenetically originated atopic predisposition. In the majority of cases, a child who is affected has a parent who suffers from atopy, that is to say atopic eczema, asthma or allergic rhinitis, also known as hay fever. Atopy refers to a person's tendency to develop aallergic reaction to normal environmental elements (animal hair, dust, pollen...), which do not cause problems for the rest of the population. Studies have highlightedanomalies affecting the gene coding for filaggrin, as well as other molecules necessary for the proper functioning of the stratum corneum. This atopy is caused by adysfunction of the skin barrier, due to a lack of sebum, lipids and cell adhesion molecules production, which can no longer play its protective role. Environmental allergens therefore easily penetrate the epidermis and provoke an abnormal inflammatory reaction.

Regarding psoriasis, 30% of cases correspond to familial forms involving genetic predispositions. The major gene involved is the PSORS1 locus. Other minor genes also play a role. The genetic variants associated with psoriasis are located in genes involved in immunity, which leads to a immune system imbalance causing chronic skin inflammation and an overproduction of keratinocytes.

As previously mentioned, these diseases are chronic inflammatory skin conditions caused by genetic predisposition. However, environmental factors also come into play: these are multifactorial diseases. The prevalence of eczema has increased in recent decades. It appears that environmental factors play a role in this increase. These could be therise in pollution, increased hygiene levels, a greater presence of allergens (pets, dust mites), changes in dietary habits etc. However, it seems difficult to estimate the weight of these factors. As for psoriasis, the involvement of external factors is clearly established: medications, infections, mental stress or even lifestyle habits (alcohol, tobacco) can trigger or worsen psoriasis.

Thus, eczema and psoriasis are both inflammatory diseases promoted by a genetic predisposition. External factors are also involved in their pathophysiology.

Non-communicable diseases.

There are many misconceptions surrounding eczema and psoriasis, particularly the belief that they are contagious. This lack of understanding leads to the stigmatisation of those affected, resulting in social isolation. It is important to know that these two conditions are not contagious. Indeed, they are of an inflammatory and non-infectious origin.

A psychological impact.

Although the manifestations of these two dermatoses are primarily physical, they have a significant psychological impact. Indeed, like many chronic diseases, eczema and psoriasis can sometimes negatively affect quality of life, causing sleep disturbances, social withdrawal, irritability and even depressive syndrome. This negative impact is due to the unsightly appearance of skin lesions, the itching they cause, and the stigmatisation.

Eczema and psoriasis: these two conditions are not confined to the skin alone.

Contrary to what one might believe, psoriasis and atopic eczema are not confined solely to the skin. In the case of atopic eczema, this dermatosis is often associated with allergic rhinitis, food allergies and asthma attacks.

In individuals with psoriasis, a quarter suffer from joint involvement: this is referred to as psoriatic arthritis. This condition is characterised by chronic inflammation of the joints, which swell and deform. Furthermore, certain diseases, particularly cardiovascular and metabolic diseases, are strongly linked to psoriasis. This includes hypertension, obesity, diabetes, and dyslipidemia.

A different age of onset.

Traditionally, atopic dermatitis appears around 3 months of age and improves or even disappears at puberty.Psoriasis is a disease that affects mainly adults, with a peak onset between 20 and 40 years old. However, be aware that genuine cases of atopic eczema can start in adulthood, and there are infants who suffer from psoriasis. Atopic eczema can persist into adulthood.

A differing localisation of plaques.

In babies, atopic eczema is primarily located on the face, the scalp and the buttocks. Later on, it can be found in the creases of the elbows, the neck or the knees (popliteal fossa), as well as on the hands and around the mouth.

In relation to psoriasis, the lesions are located in the areas of friction, that is to say the knees (kneecaps), the elbows, the navel, the loins, the buttocks and the lower back. They can also be observed at the level of the nails.

There are areas such as the scalp or the auditory canals that can be affected in both diseases.

The appearance of patches: some differences.

Eczema and psoriasis are both dermatoses characterised by the appearance of inflammatory red patches. However, they can be differentiated, as psoriasis patches are covered with thick, adherent whitish scales, which are very characteristic of this disease. Indeed, these result from an excessive proliferation of keratinocytes. Furthermore, psoriasis patches are well defined.

Eczema patches are ill-defined, erythematous patches that display vesicles. Most often, these vesicles rupture, leaving behind erosions that ooze, then become covered with crusts. Over time, scaling is observed. In cases of chronic eczema, the skin thickens: this is known as lichenification.

Note : Scales can also be found on eczema lesions, particularly during the desquamation phase. However, these are not characteristic of this disease and are less thick.