Abstract: A layer can be formed on skin, mucous membrane or other tissue by first applying an ointment on the skin or mucous membrane, said ointment containing a water-soluble alginate and an aqueous dispersion of hydrophilic lipid crystals. A calcium salt is then applied on the surface of the ointment, which converts the alginate to insoluble calcium salt. Pharmaceutically active components may be included in the ointment.