Leather, like other absorbent materials, is vulnerable to mildew and its unpleasant effects. A leather sofa may become the victim of mildew if placed in a humid environment or in a home with poor insulation or flooding problems. Even if you remove the visible mildew traces, you may still smell the familiar and unpleasant aroma that commonly accompanies mildew. Removing it will require some work on your part.
Prepare a mixture of one part rubbing alcohol and one part warm water. Mix well in a clean spray bottle. Using a light mist, spray the liquid onto a clean sponge or soft cloth. The sponge or cloth should be just slightly damp, not soaking wet.
Remove all cushions from the sofa and wipe the interior and exterior of the sofa. Make sure to wipe all area surfaces, even if they do not have visible mildew; they may contain trace mildew spores. Wipe the cushions thoroughly.
Place your leather sofa and cushions outside in the sun. Allow them to remain until they thoroughly dry. Brush the sofa and cushions before you bring them indoors.
Use heat to dry the sofa and cushions if you cannot set them outdoors. Place a dehumidifier beside the sofa, turned to its highest setting, or use a space heater.