Pharmaceutical compositions of Usnea barbata and the use thereof for the treatment of skin diseases are disclosed. A preferred composition is the combination with an extract of Hypericum perforatum. The extracts are obtained by supercritical high-pressure extraction with spring carbon-dioxide. A preferred form of preparation is the homogenization of 6% by weight of an extract of Usnea barbata, containing 96% of usnic acid, and 40% by weight of an extract of Hypericum perforatum, containing 39% of hyperforin, together. The pharmaceutical composition leads to a potentiation of the anti-inflammatory and antimicrobial effects of the extracts and to stabilization of the hyperforin. The combination is suitable for the external and internal treatment of various skin diseases, in particular skin inflammations and skin ageing, and for the treatment of skin infections with pityrosporon yeast fungi, acne and rosacea.