Answers:
This question is missed 41% of the time by FM residents, an amazing rate for such a simple question. And the answer is #1 - nickel. Boring but true. đ
The common misses on the question are all over the place. Weâre suspicious that students overcomplicate the question stem, thinking about all the causes of contact dermatitis - which are legion. Or possibly allergens encountered in healthcare settings, which would be âglovesâ (rubber accelerators).
This is exactly the sort of question you will encounter on exams - so try to read question stems as-is, without expanding them mentally.
Why This Question Is Often Missed
â Focusing on plantârelated allergies
Many students immediately think of poison ivy because itâs a classic type IV hypersensitivity, overlooking that nickel exposure is far more ubiquitous.
â Conflating latex and contact dermatitis
Latex allergy is often taught early but usually manifests as an IgEâmediated reaction rather than classic allergic contact dermatitis.
What the Distractors Indicate
| Option | What It Tests / Implies | Why Itâs Wrong Here |
|---|---|---|
| Mercury | Heavyâmetal contact allergy awareness | Mercury allergy is very rare compared to nickel. |
| Clothing dyes | Knowledge of textile/dye allergens | Disperseâdye hypersensitivity exists but is far less common. |
| Poison ivy | Classic plantâinduced contact dermatitis | Poison ivy (urushiol) is common but not as prevalent as nickel exposures. |
| Latex | Allergy related to rubber products | Latex reactions are typically immediate (type I), not the delayed type IV seen in ACD. |
High-Yield Pearl
Nickel is the single most common cause of allergic contact dermatitis worldwide due to its ubiquitous presence in jewelry, coins, and metal fasteners.
Core Learning Objectives
The âTest Trickâ at Play
This question exploits availability bias: students recall dramatic or âtextbookâ examples (poison ivy, latex) and overlook the far more common, everyday culpritânickel.
Additional Practice Questions and Remediation
Question 1
A 25âyearâold woman presents with a pruritic rash on her earlobes that began 2 days after she switched to a new pair of inexpensive earrings. What is the most likely allergen?
A. Nickel
B. Formaldehyde
C. Paraben preservatives
D. Fragrance mix
Question 2
A dental assistant develops itching and redness on her hands after wearing powdered latex gloves all day. Patch testing reveals a positive reaction to thiuram mix. What type of exposure most likely caused her dermatitis?
A. Thimerosal in vaccines
B. Rubber accelerator in glove manufacturing
C. Formalin in dental impressions
D. Paraphenylenediamine in gloves
Question 3
A 40âyearâold gardener presents with vesicular hand dermatitis after clearing ivy in her yard. Which agent is responsible?
A. Nickel
B. Urushiol
C. Chromium in leather gloves
D. Benzocaine in topical creams
Question 4
After switching to a new black sock brand, a patient develops an itchy, scaly rash on his ankles. Patch test is positive for disperse blue 106. What is the allergen class?
A. Clothing dye
B. Plasticizers
C. Formaldehydeâreleasers
D. Acrylates
Question 5
A 30âyearâold jeweler presents with pruritic papules on his fingertips after working with watch bands. Which patch test series is most appropriate?
A. Fragrance series
B. Metal (baseline) series
C. Rubber glove series
D. Photopatch series
Mini Case Discussion Prompt
Compare a patient with chronic periâumbilical dermatitis from nickelâcontaining belt buckles to one with acute vesicular hand dermatitis from poison ivy. What differences in history, timing, lesion morphology, and management would you expect?
Frequently Asked Questions (FAQs)
This question appears in Med-Challenger Family Medicine Review with CME
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