Aromatic groups are key mediators of protein-membrane association at cell surfaces, contributing to hydrophobic effects and p-membrane interactions. Here we show electrostatic and hydrophobic influences of different aromatic ring substituents on membrane affinity and cell permeability of helical, cyclic and cell penetrating peptides. While hydrophobicity is dominant, subtle changes in electrostatic surface potential, dipole moment and polarizability are shown to enhance peptide affinity for phospholipid membranes and uptake into cells. A combination of fluorine and sulfur substituents on an aromatic ring induces a dipole that enhances cell uptake of a 12-residue peptide inhibitor of p53-MDM2 and a cell-penetrating cyclic peptide. These aromatic motifs can be readily incorporated into amino acid sidechains of peptides to enhance their cell membrane activity. This work has been published in Angew Chem Int Ed Engl. 2022 Jul 18; 61(29): e202203995.