Education on Contact Dermatitis and Patch Testing

What is Contact Dermatitis?

Contact dermatitis is an inflammation of the skin at the area of contact. There are two types of contact dermatitis – irritant and allergic. Symptoms include itching, redness, warmth, swelling, cracking, pain, scaling and crusting. Skin can crack, bleed and ooze, depending on the severity of the reaction. Dermatitis can occur from exposure to the environment (such as dry weather), chemicals (such as harsh soaps), allergens (such as nickel) and physical trauma (such as abrasion). Your physician may diagnose irritant or allergic contact dermatitis from your medical history, occupation, symptoms, and patch testing. Treatment of both irritant and allergic contact dermatitis is based on avoiding contact with the substance(s) that caused the reaction.

What is Irritant Contact Dermatitis (ICD)?

This non-specific inflammatory condition develops after skin is exposed to substances that are physically, chemically or mechanically traumatizing. Symptoms are usually confined to the area of contact, recur with additional irritant exposure and may be difficult to distinguish from allergic contact dermatitis.

Irritant contact dermatitis occurs in response to irritating substances such as household cleaners, harsh soaps and industrial solvents. Your skin can react to these substances within minutes or hours, and stops reacting soon after they are gone.

What is Allergic Contact Dermatitis (ACD)?

Allergic contact dermatitis occurs from a person’s immune response to contact allergens, such as fragrances, preservatives, nickel, gold, and many others. Allergic reactions to contact allergens develop hours or days after exposure, and may take weeks to heal. A personal or family history of other allergies may increase a person’s chance of developing this skin condition.

In already sensitized individuals, this immunologic response is elicited by contact with a specific allergen or closely related chemical. Symptoms typically manifest 24 to 72 hours after allergen exposure, vary in intensity and often include itching and vesiculation. More than 3,000 chemicals are reportedly capable of causing allergic contact dermatitis but relatively few allergens account for most cases. These common allergens form the basis of diagnostic patch testing that is used to differentiate allergic from irritant contact dermatitis.

Allergic contact dermatitis is responsible for approximately half of all contact dermatitis cases. Patients with persistent, unresolved contact dermatitis can suffer for years with a diminished quality of life and increased medical treatment costs. However, the condition can be effectively treated once an accurate diagnosis is obtained.

How Prevalent is Contact Dermatitis?

Allergen exposure is influenced by climate, occupation, cultural habits, and regulations. The prevalence of contact allergy against specific allergens differs among countries as a result in changes and developments in surrounding environments and societies.

Recent meta-analysis (Alinaghi F, Bennike NH, Egeberg A, Thyssen JP, Johansen JD. Prevalence of contact allergy in the general population: A systematic review and meta-analysis. Contact Dermatitis. 2019;80:77–85.) confirmed that at least 20% of the general population in Europe are contact-allergic to common environmental allergens. In the general population, with overall higher estimates in women than in men. Despite a tendency for slightly higher estimates in adults than in children and adolescents, the difference was not significant. Contact allergy to nickel and other metals was most common, but fragrance allergy was also observed in a large proportion.

In the UK, occupational contact dermatitis is the most frequently reported occupational skin disease in developed countries and accounts for between 70% and 90% of all reported cases of occupational skin disease. The annual population incidence of occupational contact dermatitis ranges from an estimated 5.7 to 101 cases per 100,000 workers per year. The most reliable studies estimate the incidence to be between 11 and 86 cases per 100 000 workers per year. (Nicholson et al. 2010) Experts believe these numbers may underestimate the impact of contact dermatitis.

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