A 16-year-old man noticed asymptomatic blue-gray patches on his trunk a month before visiting our clinic. The lesion gradually increased in size and number. Clinical examinations were normal and histopathological examination showed melanin deposition in the dermis. The patient was diagnosed as ashy dermatosis based on clinical and pathological findings. The lesion did not respond to 4-month oral ascorbic acid and tranexamic acid therapy. Although there is no established treatment for ashy dermatosis, it was reported that removal of the causative factors improved the symptom when the causes of onset were identified. Therefore, detailed history taking would be important in diagnosing ashy dermatosis.
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