In order to provide an electrochemically active unit for an electrochemical device including a membrane electrode assembly, at least one gas diffusion layer and a seal that is linked to at least one of the at least one gas diffusion layers, in the manufacture whereof as even as possible a construction of the penetration region in which the gas diffusion layer of the electrochemically active unit is penetrated by the sealing material of the seal over the periphery of the gas diffusion layer is achievable, the seal includes a linking region, a distribution region and a connection region that connects the linking region and the distribution region to one another, wherein the connection region has a minimum height that is less than a quarter of the maximum height of the distribution region and less than a quarter of the maximum height of the linking region.