Hydrotropes: Solubilization of nonpolar compounds and modification of surfactant solutions

•The review covers hydrotrope research history and terminology.•Substantiated knowledge about hydrotropy mechanism is shown and current hypotheses are outlined.•Salting-in/out, hydrotrope aggregation, hydrotrope-solute complexes, co-solvent effects and water structure are discussed.•Hydrotrope interaction with surfactants and concomitant morphological transitions are covered.•Flexible stimuli-responsive self-organized hydrotrope-surfactant systems with tweakable aggregation behavior are covered.