1.1.2.3 Irritant Contact Dermatitis

Irritant contact dermatitis. Irritant dermatitis. Irritant contact eczema.

Non immunologic contact dermatitis.

Cumulative toxic dermatitis, “wear and tear” dermatitis.

Point prevalence about 1- 2% in the healthy population.

ICD is caused by chemicals, which damage skin structures in a direct non-allergic way. It is a dose dependent reaction from exposure to irritants (chemical and/or physical). The most frequent chemical irritative factors are long lasting and repetitive contact with water (“wet work”), detergents and/ or solvents. Skin barrier perturbation facilitates irritant substances to penetrate the stratum corneum causing cytotoxic effects on keratinocytes and release of cytokines and chemokines. The innate immune system is activated, and ICD reaction is initiated, however, the immunological cascade of priming (for example T-cells of the helper cell type) does not occur.

For acute ICD, the reaction is often caused by a single exposure and usually resolves within days to weeks. Release of pro-inflammatory mediators, including cytokines (IFN-γ, IL-4 and IL-17), resulting in vasodilatation and cell infiltration. Spongiosis leads to vesicle formation, erythema, induration and edema. Chronic ICD is a multifactorial disorder involving exogenous and endogenous factors. Endogenous factors include variations in the skin barrier structure and composition, innate immunity reactivity variations and an atopic background. A history of atopic dermatitis quadruples the risk of hand eczema when skin is exposed to wet work. Some genetic risk factors have been detected.

The morphology of cutaneous irritation varies widely and depends on the type and intensity of the irritant(s). The following types can be described:

• Acute ICD

• Chronic ICD

Folliculitis, miliaria, pigmentary alterations, alopecia, contact urticaria or granulomatous reactions that may result from irritants are not considered ICD.

Chemical insults to the skin may develop after exposure to potent acidic or alkaline substances. Severe tissue damage may result even after a short contact. Initial painful cutaneous whitening and edema, followed by necrosis and scarring is usually observed.

An irritant reaction is often monomorphous (erythema, wheals, papules, pustules), but may vary according to the type of exposure, body region and individual susceptibility.

The clinical signs of acute ICD include erythema, edema, inflammation and vesiculation. ICD can be clinically indistinguishable from the allergic type. Symptoms may range from mild erythema through exudative cutaneous inflammation to ulcerative lesions and epidermal necrosis. Acute ICD usually exhibits an asymmetrical distribution and sharply demarcated borders. Some chemicals may produce delayed acute irritation (8-24 hours or more after exposure).

Chronic ICD shows erythema and increasing dryness (xerosis), followed by hyperkeratosis with frequent fissuring and occasional lichenification. The lesions are usually localized but ill defined. Pruritus and pain due to fissures are symptoms of chronic ICD. Hand eczema is a common clinical presentation.

ICD can involve any area of the body surface in contact with the irritant. The lesions are usually well-demarcated and confined to the area of contact with the irritant, even if in selected cases some spreading may occur (e.g., from the hands to the forearms). The hands, the interdigital spaces and dorsal side of the hands and fingers are the most common locations for chronic ICD and many times show an occupational relevance.

Contact dermatitis is defined as inflammation of the skin involved as a result of exposure to an exogenous agent and is generally divided into irritant contact dermatitis (ICD) and allergic contact dermatitis (ACD).

Clinical classification of ICD is based in the clinical diversity according with both morphology and mode of onset. The various forms of ICD include: acute ICD, delayed contact ICD, irritant reaction, chronic ICD, traumatic ICD, acneiform ICD, non-erythematous irritation, subjective or sensory irritation, friction dermatitis and asteatotic irritant eczema.

Patch testing is mandatory if the ICD is present for more than 3 months. Patch test results may help to differentiate an allergic from an irritative reaction.

Less frequent ICD clinical manifestations include purpuric reactions caused by metallic salts (cobalt chloride), and pustular reactions with metals (chromium, cobalt, and nickel). Although in most cases a negative result excludes a contact dermatitis, in case of a high suspicion of sensitization, the possibility of a false negative result should be considered.

Several diagnostic tests to evaluate the individual susceptibility to irritants are not used in clinical practice. These are: alkali resistance (sodium hydroxide), ammonium hydroxide, dimethylsulfoxide, threshold response to various irritants (sodium lauryl sulphate, nonanoic acid, etc), lactic acid stinging, minimal erythema dose with UVB or measurement of transepidermal water loss (TEWL).

Irritants produce a variety of histopathological changes (epidermal single cell and complete necrosis, spongiotic dermatitis). Irritants can induce necrosis of keratinocytes, which may become confluent, and the intraepidermal vesicles soon develop into vesiculo-pustules with dermal and epidermal inflammatory infiltrate mainly constitute by lymphocytes and also neutrophils. The pattern may be different according to concentration of the irritant, type, duration of exposure, and individual reactivity of the skin. ICD shows much greater histological pleomorphism than allergic contact dermatitis (ACD).

The course can be acute or chronic depending on the concentration and length of exposure to the exogenous substance. Lesions of ICD heal rather quickly if the triggering agent(s) are removed (‘decrescendo’ phenomenon). High-risk professions are nursing, hairdressing, food processing, construction work, etc. ICD can be occupationally relevant.

The frequency, duration and form of contact to irritants can influence in the course of the disease. Decreasing the frequency of contact to an irritant is a crucial factor in individual measures of prevention and can be achieved by appropriate hand washing and hand protection at working place. An occlusive contact potentiates the irritant effect. Temperature is also a relevant factor and mechanical irritation promotes chemical irritation. The simultaneous action of different irritants may potentiate the intensity of irritation.

ICD favours the risk of contact sensitization and the development of a secondary allergic sensitisation. Eczematous skin also is prone to be infected (impetiginization).

Differentiation between ICD and ACD is frequently very difficult on the basis of clinical morphology only. The clinical picture in both conditions may include erythema, vesicles, lichenification, excoriations, scaling and hyperkeratosis. Distinguishing irritation from allergy is complicated, since many allergens have irritant effects and both types of contact agents act jointly. A careful history, thorough knowledge of the patient’s chemical and physical factors environment, and patch testing will be helpful in differentiating between both disorders.

ICD should be differentiated from an immediate type of stinging (e.g., induced by alcohol). This develops after exposure and abates quickly within seconds or minutes. Delayed stinging builds up over a certain length of time, does not disappear after removal of the causative agent, occurs frequently in the face when sweating and is experienced primarily by predisposed individuals (“stingers”). These individuals can be identified by a positive response to 5% lactic acid. They are often fair-skinned, have history of “sensitive” or “dry” skin and reveal an atopic background.

Other differential diagnoses in particular on palms and soles are chronic psoriasis, eczema in psoriatic and palmo-plantar keratodermas as well as cutaneous T-cell lymphoma.

The most important therapeutic approach in the treatment of ICD is the identification of the causative chemicals, climatic and mechanical factors. Mild forms may be controlled by the regular use of emollients/ moisturizers. Severe relapsing forms require corticosteroids, topical calcineurin inhibitors, ultraviolet light treatment and close adherence to prevention strategies.

Primary to tertiary preventive measures are necessary. For prevention, irritants do not always have to be avoided completely. A reduction of the duration and frequency of contact is sufficient. This reduction can mostly be achieved by correct use of individual skin products like gloves or protecting clothing but must be supported by correct education and continued motivation of employees. When ICD is of occupational relevance, cessation of the implicated activity may be required, particularly if the patient´s compliance is low. Preventive measures are necessary in and out of work.