Contact dermatitis is a skin disease that occurs due to exposure to external irritants or allergens. Also known as contact eczema, it is marked by a characteristic itchy (pruritic), rough, scaly (in well-defined plaques), reddened and inflamed skin condition.

Types of contact dermatitis

Irritant contact dermatitis (ICD): Around 80% of all contact dermatitis conditions are of this type. ICD is caused when the skin comes in contact with some toxic substance generally in the form of irritant chemicals found in soaps, solvents, acids, or alkalis. This apart, these chemicals can also be found in personal care preparations, plants, topical applications, home made therapies or chemicals one is exposed to in certain occupations.

Allergic contact dermatitis (ACD): ACD makes up the rest of the 20% of contact dermatitis cases. ACD is a late-onset hypersensitivity of the skin when it is exposed to chemicals to which a patient has been intolerant for some time.

The kind of reaction of the skin in the case of ACD and ICD is determined by the causative chemical, the extent and nature of exposure, and the individual patient’s sensitivity. However, one must be cautious while distinguishing between ICD and ACD, since they have almost identical clinical features particularly in the chronic condition.

Apart from ICD and ACD, there are two other variants of atopic dermatitis which are:

Systemic contact dermatitis: This occurs when a patient with a history of contact allergy becomes exposed to an irritant chemical through a systemic means, for example an injection, oral, intravenous, or intranasal application.

Airborne contact Dermatitis: This is caused by airborne allergens (mainly from plants, plastics, glues, rubbers, metals, insecticides, pesticides etc) for example ragweed dermatitis that mainly occurs on the face.

Diagnosis and differential diagnosis of ACD

The best way to differentiate between ICD and ACD is a through a patch test. Patch tests ascertain the type of allergen involved or an allergy contact with the irritant agent.

Many patients often do not seek medical help especially in case of ACD from obvious causes like jewelry, poison ivy, nickel, etc. However, in many cases, easy identification of the cause and a clinical history is not enough to determine the allergens and herein patch tests and skin examinations are required. For instance, a patient who presumably suffers from chronic hand dermatitis is unaware that it is actually being caused by a personal care product.
Though patch testing is the mainstay of the clinical diagnostic procedure in ACD, histology is also often necessary. This is also an integral part of differential diagnosis especially to distinguish atopic dermatitis from cutaneous T-cell lymphoma. The differential diagnosis of ACD must also exclude other kinds of dermatitis such as ICD, stasis dermatitis, seborrheic dermatitis, and acne rosacea. This apart, hand and foot ACD must be differentiated from psoriasis and fungal infections.

In patients reporting widespread occurrence of the disease, it must also be distinguished from other causes of erythroderma. But the diagnosis is incomplete without a thorough knowledge of the clinical characteristics of the condition. In case of ACD they are:

• Typical marked out itchy (pruritic), rough, inflamed (eczematous) skin flares. These eruptions are sore and swollen in acute cases or in the form of flaking plaques in chronic conditions.
• ACD eruptions are characteristically restricted to skin locations that come in contact with the irritant. However, one must be aware that often there is irregular or scattered distribution of the eruptions, depending on the triggering allergen. For instance, liquid washes or shampoos that the entire body is exposed to may result in more spread out eruptions.
• Urticaria, systemic reactions and photosensitive reactions are some of the less prevalent occurrences.

From the pathological angle, in the acute phase of ACD there is a random amount of skin spongiosis (spongy feeling to the skin due to increased accumulation of fluid in the affected skin). In moderate to acute conditions, distinct spongiosis leads to the formation of intraepidermal blisters or vesicles. In the subacute to chronic stages, one can also see epidermal hyperplasia and psoriasiform skin.

Prevalence

Any person of any age and any ethnicity can develop ACD. There are some gender differences but it is mostly determined by the kind of exposure. For instance, women are more prone to nickel allergy since they wear more jewelry than men do. A person’s vocation also has a big role to play in the development of ACD. In addition, prevalence of irritants can differ according to geographical locations and climatic conditions. Again, since preservatives have a major role to play in ACD, it may differ in form in different places depending on the local official directives about their use in personal care preparations.

Common Allergens

The major 10 allergens recognized by the North American Contact Dermatitis Group (NACDG) are:

• Nickel sulfate
• Neomycin sulfate
• Balsam of Peru (Myroxylon pereirae)
• Fragrance mix
• Thimerosal
• Sodium gold thiosulfate
• Formaldehyde
• Quaternium-15
• Cobalt chloride
• Bacitracin 13

The number one drug category that causes atopic dermatitis is corticosteroids. Corticosteroids are anti-inflammatory medications that cause ACD in an estimated 0.2% to 5.98% of people who use them. It is probably the number one drug category for causing atopic dermatitis because the use of corticosteroids is so widespread and common.

Treatment and Patient Counseling

Patient education form doctors should typically include the following or something similar:

• Written details about the allergens and their effects .
• How to read the labels of products so as to avoid exposure to irritants.
• How to identify and avoid allergens one is vulnerable to.
• How to trace the allergens present in the surroundings, say for instance a spray that your spouse uses and you are unknowingly allergic to.

Treatment of ACD involves:

• Identification of the causative allergens (primarily through patch tests).
• Primarily application of topical corticosteroids and secondarily systemic corticosteroids.
• Avoiding the allergens after the course of medication is over.