Compositions and methods are disclosed for preventing or reducing frizzy appearance of keratin fibers, including hair, and reducing the amount of fly-away strands of hair, particularly in humid conditions, by forming a coating on hair that is resistant to water vapors from the air or surrounding environment. The compositions comprise a combination of a hydrophobic particulate material comprising a hydrophobically surface-modified aluminum oxide and one or more hydrophobic film formers in a cosmetically acceptable vehicle.