Although extracts from Hamamelis bark have long been used in therapy of skin diseases and in cosmetic formulas there are only few pharmacological investigations verifying the activity of distinct Hamamelis bark constituents. Therefore two major classes of constituents, namely polymeric proanthocyanidins and polysaccharides were isolated from Hamamelis bark and tested concerning their influence on proliferation and differentiation of cultured human keratinocytes. While the polysaccharide fraction, consisting mainly of arabans and arabinogalactans, did not effect human keratinozytes, the proanthocyanidins strongly increased the proliferation of the cells, while the differentiation was not influenced significantly. Within a preliminary cumulative in vivo study on SLS-irritated skin, proanthocyanidins (ProcyanoPlus) were proven to reduce transepidermal water loss and erythema formation. Furthermore, a clinical scoring indicated that procyanidins can influence irritative processes significantly.