Contact dermatitis: Clinic, diagnosis and treatment

• Contact dermatitis is a form of eczema that develops following exposure to an allergenic substance.
• It is characterized by itching, redness, blistering and cracking of the skin on the exposed area^1-3.
• The pathological process involves a deregulated immune response in the skin, which results in inflammation of the skin.
• Risk factors include a history of atopy, a family history of skin allergies, and frequent exposure to sensitizing substances such as perfumes, cosmetics, metals, etc^1-3.
• Diagnosis is often based on medical history and clinical symptoms and may be confirmed by patch testing.
• Treatment usually consists of avoiding exposure to the allergenic substance, using topical medications to reduce inflammation and itching, and maintaining good skin hydration^1-3.
• Contact dermatitis can be successfully managed if diagnosed and treated appropriately. However, without proper treatment, it can lead to long-term complications such as bacterial infections and scarring^1-4.

• The physiopathology of contact dermatitis involves a dysregulated immune response of the skin following exposure to an allergenic substance.
• When the skin is exposed to an allergenic substance, immune cells called dendritic cells capture these substances and present them to T-cells.
• The T-cells, in response, activate immune cells called B-cells, which produce antibodies to the allergenic substances^1,2.
• This immune response also triggers the release of pro-inflammatory molecules such as cytokines, chemokines and inflammatory mediators, which cause a local inflammatory reaction.
• This inflammation leads to symptoms such as itching, redness, blistering, and skin fissures^1,2.
• In some cases, the immune response can also lead to cross-sensitization, which means that the skin may react to substances similar to those that caused the original contact dermatitis^1,2.

• Contact eczema can take several different clinical forms, depending on the allergenic substance involved and the duration of exposure.
• The clinical appearance varies according to the site and the length of time the allergy has been present.
• The eczema is initially acute (raised, red, vesicular patch with crumbled edges, opposite the pathogenic contact) and progressively evolves towards a dry, thickened appearance (lichenification).
• The face is usually affected by edematous lesions. Pruritus is always present and sometimes very severe.
• The lesions often extend beyond the contact area (e.g. involvement of the wrists and forearms in hand eczema).

Examples of common forms of contact eczema^3,4

Contact allergy to nickel

• It affects 10% of European women. It is related to the wearing of costume jewelry rich in nickel (necklace, ring, earrings...).
• We must not forget however the presence of nickel in 11 or 14 carat gold and the late onset of eczema after wear and tear of the plating of gold-plated jewelry.

Facial allergy linked to cosmetic creams

Currently, preservatives or perfumes are the most common cause.

Allergy of the face and scalp

Linked to shampoo components (e.g.: cocamidopropyl betaine).

Allergy of the sides of the neck

Due to perfume spraying.

Allergy of the armpits

Due to deodorants of all types.

Sofa dermatitis

• Due to armchairs, but also to shoes or leather clothes whose preservative is dimethyl fumarate (DMF).
• These materials manufactured in China and exported to France have triggered severe, persistent forms of eczema with sometimes a general syndrome.

Temporary tattoo eczema

Widely in vogue in tourist sites, it uses black henna rich in paraphenylenediamine (PPD is a classic allergen of hair dyes) which leads to a symptomatology corresponding to an acute eczema usually bullous overlaying the tattoo but especially a scarring aspect most often achromic and sometimes hypertrophic.

Specific forms

The hand-carried form

The allergen is handled by the hands and worn on the face or other parts of the body, triggering eczema.

The airborne form

The allergen is carried by the wind and triggers eczema on areas not protected by clothing, usually the neck and face (e.g.: eczema caused by the stinging hairs of processionary caterpillars).

The proxy form

The allergen is carried by the spouse and transmitted to the partner during contact. (ex.: perfume, lipstick).