Cell membranes fulfil many important biological functions and are composed by an heterogeneous variety of lipids and proteins, which leads to the typical asymmetric bilayer structure. One of the main functions of cell membrane is to act as a filter to control the molecules traffic at the interface. The comprehension of the molecular transport across the membrane is hugely important in medicine, in particular in the development of effective drug delivery system. There are different routes for cellular uptake, some involving complex signalling pathways, some more simple. The easier way is the direct translocation through water pores. Indirect experimental evidences suggest the presence of small, short-lived pores for which todays experimental tools are unable to provide direct observation and atomistic detail.