A 12-year-old boy with type 1 diabetes mellitus and coeliac disease reported 2–3 months of skin darkening at his insulin pump cannula and continuous glucose monitor sites (figure 1). For the preceding 9 months, he had localised itching and redness, which had been managed as allergic contact dermatitis by a dermatologist. He continued to use the dressings and these symptoms had improved. Hyperpigmentation was noted over his knuckles and periorally. He had no symptoms of adrenal insufficiency and …