The commonest reason a topical corticosteroid appears to fail is that the patient was given 15 g for a body-wide eczema and made it last a month. Potency gets discussed; quantity almost never does.
Use the fingertip unit: the amount squeezed from a standard 5 mm nozzle over the distal phalanx, about 0.5 g, covers two adult palms. A whole adult body takes roughly 20 to 30 fingertip units, or about 20 g, per single application. Twice daily for two weeks over trunk and limbs is therefore several hundred grams, not one tube. Write the quantity on the prescription and say it aloud.
The corollary is the other failure mode. A patient who returns having used 100 g of a potent steroid on the face in a month has a different problem, and the answer is a site-appropriate potency and a written tapering plan rather than a stronger preparation. Both errors come from the same gap: telling people what to apply without telling them how much.
- One fingertip unit is about 0.5 g and covers two adult palms
- A whole-body adult application is roughly 20 to 30 fingertip units
- Write the total quantity on the prescription, and check at review how much was actually used
- Match potency to site: mild on face and flexures, potent on palms, soles and lichenified plaques
- Demonstrate application once in clinic — it changes adherence more than any leaflet
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