Dryness of keratin materials, in particular dryness of the skin, and especially disorders associated with dry and/or hyposeborrheic skin are treated by administering to individuals afflicted therewith, thus effective amounts of at least one extract of a non-photosynthetic and non-fruiting filamentous bacterium cultured in a medium which includes at least one non-sulfurous mineral and/or thermal water, e.g., an extract derived from the bacterium Vitreoscilla filiformis, in particular the strain ATCC 15551, cultured in a medium enriched with water from La Roche Posay.