The steroid is in a special chemical form ( a diester ) that makes it effective at low doses in skin conditions as the medicine is able to get into and remain longer in the outer layer of the skin .. This sentence is hard to understand. A simpler version with equivalent meaning is the following:
The steroid is in a special chemical form ( a diester ) which allows it to be effective in low doses for skin conditions . This is because the drug can penetrate the outer layer of the skin and stay there longer .