Irritants and Allergens: When to Suspect Topical Therapeutic Agents

Introduction

The subject of contact dermatitis tends to polarize dermatologists into one of two camps. There are those who seem to live for the mere suggestion of patch-test placement whereas others cringe at the thought of it. It is the author’s opinion that the answer lies primarily in how contact dermatitis is learned. Many practitioners do not enjoy the subject of contact dermatitis because it is often viewed as a subject requiring memorization of hundreds of chemicals with little clinical utility. This chapter will present somewhat of a paradigm shift with regard to the approach to managing contact dermatitis. The focus will be to de-emphasize rote memorization of contact allergens, emphasizing instead the core knowledge that can be broadly applied by dermatologists to various clinical scenarios.

Contact Dermatitis: the Concept

It has been reported that 6% to 10% of all dermatology visits are as a result of contact dermatitis. Q56.1 One of the core concepts is that the term contact dermatitis is broad and is used to include allergic contact dermatitis (ACD), irritant contact dermatitis (ICD), and the much less common contact urticaria. We will only discuss ACD and ICD. Within these subgroups almost any morphologic reaction on the skin is possible. However, eczematous reactions are most common—either acute eczematous eruptions (such as poison ivy) or chronic eczematous eruptions such as typical cases of chronic hand dermatitis. The general rule of thumb is that of all cases of contact dermatitis, 80% are irritant and 20% are allergic in nature.

Q56.2 The term contact dermatitis medicamentosa is used when the allergen source is found to be a medicament (something used to treat, prevent, or alleviate the symptoms of disease).

When to Suspect Contact Dermatitis

Q56.3 Contact dermatitis should be suspected in any pruritic or painful cutaneous eruption that is refractory to conventional therapy. Although symptomatology is not specific, ACD tends to be associated with more pruritus and ICD is more likely to be reported as painful or uncomfortable. A thorough history coupled with a high index of suspicion is required in refractory, worsening, or intermittent flaring cases of dermatitis affecting any body site. Certain anatomic sites have a high incidence of contact dermatitis and should be considered to indicate a relatively high yield for patch-testing. Such sites include eyelids, lips, perioral area, neck, axilla, hands, feet, anogenital region, and lower legs. Contact dermatitis is much less likely to occur exclusively on the trunk, proximal extremities, and scalp. These latter distributions should reduce the suspicion of contact dermatitis and increase the suspicion of an endogenous dermatitis.