The invention provides the use of extracts from algae for cosmetic and/or medical treatment of skin, including improving and enhancing the skin-barrier, anti-aging treatment and photo-protective treatment. The invention is based on the finding that extracts from algae obtainable from saline hot water sources exhibit a multi-faceted biological effect useful in the cosmetic and/or therapeutic treatment of skin for the above purposes. Specifically, it has been shown that such algae extracts induce markers (involucrin, filaggrin and transglutaminase-1) for skin barrier formation in keratinocytes, induce collagen expression in dermal fibroblasts and inhibit UVA-induced up-regulation of photo-aging markers (matrix metalloproteinase MMP-1 and cytokine IL-6).