Can you identify this asymptomatic rash?

A 16-year-old boy presents with a 1-month history of an asymptomatic rash on his sacral area. There are no other rashes on his body.

What does this look like to you?

A. Dermatophyte infection. 
B. Candidiasis. 
C. Confluent and reticulate papillomatosis.D. Psoriasis. 
E. Factitial dermatitis. 

(Answer on next page)

Answer: Factitial dermatitis

The correct answer is E. Further history taking elicits additional important information; the rash developed after the teenager started a daily regimen of sit-ups. The eruption gradually disappeared when the patient began to exercise on a thick pad instead of on carpeting.