What is responsible for persistent lip irritation?

Persistent irritation confined to the right corner of his lips annoys a 39-year-old man. He is unaware of anything that may have precipitated it. The patient takes no medication; past episodes of mild psoriasis of the elbows and knees were well controlled with intermittent corticosteroid use.

Can you identify this condition?

A. Vitamin B12 deficiency.

B. Candidiasis.

C. Contact dermatitis.

D. Psoriasis.

E. Herpes simplex.

(Answer on next page) 

Answer: Contact dermatitis

The patient revealed that he had recently started using a new toothpaste that contained a whitening agent. Discontinuation of this brand and resumption of his old toothpaste resolved this contact, or irritant, dermatitis, C, to the whitening agent.

Manifestations of vitamin B12 deficiency and candidal infections are usually bilateral. Psoriasis does not present as a perioral rash; herpes simplex features discrete vesicles on an erythematous base.