DISCUSSION
In the ’90s, a commercial for sneakers utilized the catchphrase, "It's the shoes!" And so it is occasionally with rashes on the feet. In this case, the patient was allergic to the leather on the inside of his work boots.
A true allergy such as this would be expected to itch and to manifest as a papulovesicular rash limited to areas touched by the leather on the upper portions of his shoes. And it would persist, despite the quantity of topical medications tried, because the patient wore the shoes for eight to 12 hours a day, five or six days per week, continually re-exposing his skin to the offending material. He had never taken any significant time off work and therefore hadn’t refrained from wearing the shoes long enough to allow the rash to abate.
Often, frustrated and uncomfortable patients take matters into their own hands, which can ultimately compound the problem. This patient didn't do his skin any favors with the rubbing alcohol and other products he'd tried (the most common offender being triple-antibiotic ointment, although this patient used it only on rare occasions). Another strategy these patients often employ is to soak their feet in watered-down bleach. Fortunately, this patient had considered this option but thought better of it. A more benign, but just as ineffective, attempt at self-treatment had been to change laundry detergents, which of course did nothing to resolve the rash. (His first clue should have been that laundry detergent would not affect the tops of his feet while sparing the rest of his body.)
The insides of leather shoes are usually tanned with potassium dichromate, a chemical known to provoke this kind of reaction. Even after the source of the rash was identified, however, getting some distance between the patient and his shoes wasn’t easy. I had to write him a note for work, requesting that he be allowed to refrain from wearing his boots for about two weeks.
During that time, he started a week-long course of cephalexin 500 mg tid and applied clobetasol foam twice a day. In dermatology, we assume that any longstanding wet rash on the feet will become secondarily infected or at least colonized with gram-positive bacteria. Of course, giving him the steroid foam meant we were utilizing a class 1 corticosteroid in a very drying vehicle.
Within a week, he was a new man, with almost totally clear foot skin. This still left him with the problem of the work boots and the job—but one problem at a time.
TAKE-HOME LEARNING POINTS
• The areas spared by a rash are often just as important as those that are affected.
• Laundry detergents, often blamed for rashes, are seldom the culprit.
• Fungal infections rarely affect the dorsum of the foot while sparing interdigital and plantar surfaces.
• The patient’s atopic state will likely render him/her more susceptible to allergens.
• The vehicle (cream, gel, ointment, solution, foam) and strength of topical steroids both matter.
• Patients can become sensitized to the preservatives or other chemicals in OTC or prescription corticosteroid creams.