Contact Dermatitis: Everything you need to know about this dermatological disorder.

Contacteczema is a skin allergic reaction triggered by an allergen. It is a skin inflammation that results in red patches and itching. Unlike atopic eczema, individuals affected do not have any specific genetic predisposition. Four major sources of allergens, present in our daily environment, are generally the cause of contact eczema.

• Clothing items: dyes for clothes, leather, glue, rubber, nickel accessories...

• Cosmetics: shampoos, hair dyes, nail polishes, hand creams...

• Topical medications: anti-inflammatory creams, antiseptics...

• Occupational allergens: these are allergens present in the workplace. They are the cause of occupational eczema, most often localised on the hands. Among the professions affected, we find notably the construction trades (cement, paint...), health professions (gloves, resin) and agricultural professions (pesticides, fertilisers...).

Among these allergens, some only cause contact eczema after exposure to UV rays. In this case, they are referred to as photoallergens. Cosmetic formulations are generally the cause of this type of contact eczema.

The symptoms of contact eczema can vary from one person to another. However, the progression always begins with a erythema, that is, a redness due to the dilation of the blood vessels, possibly followed by an oedema, which is a significant swelling of the skin. These initial symptoms are accompanied by a significant itching. Then appear the vesicles which undergo a rupture, leading to the crusts. The various lesions caused by contact eczema first form at the point of contact with the allergen and can then spread throughout the body. Contact eczemas are often classified into two categories, differentiated by the extent of the flare-up.

• Chronic contact eczema.

  The chronic form of contact eczema is caused by weak irritants. These require fairly long or repeated periods of skin contact to provoke irritative contact dermatitis.

• Acute contact eczema.

  The acute form of contact eczema manifests itself after just one exposure to a highly irritating allergen. This is enough to damage the skin and cause a significant burn or a stinging pain.

How can one determine if it's contact eczema or just a simple irritation?

Skin reactions to an allergen are not necessarily contact eczema. Redness can occur from simple irritation. Generally, the symptoms of contact dermatitis do not appear immediately after contact with the allergen, unlike those caused by irritation, particularly sensations of heat and burning.

As previously mentioned, contact dermatitis occurs when the skin reacts to an external irritating substance known as an allergen. The reaction progresses in two stages.

1. The sensitisation phase.

   This phase begins when the allergenic substance penetrates the skin. Once inside, it binds with natural proteins in the skin tissue to form a complex. This complex is then transported throughout the body by lymphocytes, white blood cells that are part of the immune system. Lymphocytes play a key role in recognising and neutralising germs and foreign substances thanks to the immune memory. The sensitisation phase can last from a few days to a few weeks, without visible symptoms of skin lesions.

2. The revelation phase.

   When the substance comes into contact with the skin again, the immune system recognises it. In response, the lymphocytes release lymphokines, a class of cytokines that direct the immune system's response, causing itching, redness, and skin lesions. The initial symptoms of contact eczema occur within 12 to 48 hours following exposure.

   Typically, inflammation is localised to the area in contact with the allergen, but in severe cases, it can spread to large body surfaces. Symptoms generally subside after 4 to 7 days, completely disappearing after approximately two weeks. An individual may remain sensitised for life, or their sensitivity may gradually diminish if they are no longer in contact with the allergen. Without identification of the allergen, the skin thickens and the reaction continues. In a few cases, complications may occur: bacterial superinfection, generalisation of lesions, and so on.

In the event of contact eczema, it is recommended to seek the advice of a professional. This individual will then conduct an allergy investigation to identify the allergen responsible for the dermatological disorder. To do this, they will perform skin tests, known as patch-tests.

Once the allergen has been identified, your doctor will likely prescribe a treatment based on corticosteroids to soothe and calm the inflammation. You can supplement this treatment with the daily application of an emollient, a care product designed to strengthen the skin barrier and nourish the skin.

Furthermore, to combat the itching caused by contact eczema, the application of cold compresses or natural ingredients such as thermal water or certain essential oils is recommended. These various elements have soothing properties and may somewhat alleviate the itching.

• GOLDENBERG G. & al. Eczema. The Mount Sinai Journal of Medicine (2011).

• BORRADORI L. & al. Dermatologie et infections sexuellement transmissibles. Elsevier Masson (2017).