Diffusion theory allows the production of realistic skin renderings. The dipole/multipole models allow us to solve challenging diffusion theory equations in a very efficient manner. By using texture-space diffusion, a Gaussian-based approximation, and programmable graphics hardware real-time photorealistic skin renderings can be achieved. Performing this diffusion in screen space instead offers additional advantages that make the diffusion approximation practical in scenarios like games, where having the best possible performance is crucial. However, unlike the texture-space counterpart, the screen-space approach is in principle unable to simulate transmittance of lighting through thin geometry, yielding unrealistic results in those cases. In this work we introduce a transmittance algorithm that turns the screen-space approach into a very efficient global solution, capable of simulating both reflectance and transmittance of light through a multi-layered skin model. We derive our transmittance calculations from physical equations, which are finally implemented by means of a simple texture access. Our method performs in real-time requiring no additional memory usage, minimal extra processing power and memory bandwidth. Despite its simplicity our practical model manages to reproduce the look of images rendered with other techniques (both offline and real-time) such as photon mapping or the diffusion approximation.