A slightly pruritic, pigmented rash of several weeks duration on the right side of the abdomen prompts a 27-year-old man to seek medical evaluation.
The correct diagnosis is tinea versicolor. A dermatophyte infection is in the differential for many rashes; perform a potassium hydroxide evaluation to confirm the diagnosis. A reaction to soap or detergent is more widespread and would not be confined to the abdomen; a reaction to a shirt would include most of the trunk and arms. Failure to moisturize can cause asteatotic eczema, which presents with scale. Contact and irritant dermatitis, psoriasis, and seborrhea are usually more pruritic. The distribution of this eruption is not seen in seborrhea and would be unusual for psoriasis.