Eczema in children is a chronic disabling condition. The impact of this condition on the lives of families is often underestimated by conventional physicians. As a consequence parents may investigate complementary treatment options. Close monitoring by a paediatrician is essential, considering that a variety of adverse effects can occur during the use of complementary treatment. We present a 5-year-old girl with eczema. She visited a Chinese herbalist who prescribed an ointment. The parents noticed that the eczema resolved fast, itching decreased and she was finally sleeping well. However, her behaviour changed and appetite increased. Undetectable levels of serum cortisol were found, which was indicative of exogenous Cushing's syndrome. Analysis of the ointment revealed the presence of dexamethasone. Hydrocortisone substitution and subsequently a reduction schedule were implemented, after which endogenous cortisol production recovered after 4 months. Physicians should be aware that unregistered herbal medicine can contain potent drugs such as glucocorticoids.