A non-therapeutic, non-surgical method for: (i) growing or regrowing hair on the skin and/or scalp; (ii) cleansing hair follicles and/or improving follicular delivery of active benefit agents; (iii) inducing micro-lesions on skin surface by means of cavitation bubbles to grow or regrow hair; or (iv) stimulating follicular stem cells to facilitate hair growth or regrowth, comprising the steps of: a. providing a topical composition for propagation of ultrasound waves from an ultrasound device ; b. applying the topical composition to an area of the skin or scalp in need of treatment; c. providing a device having power source and an acoustic transducer electrically connected to the power source, the transducer calibrated to generate acoustic energy at a frequency ranging from about 100 kHz to about 3000 kHz; d. orienting the device such that any ultrasound waves generated by the transducer are projected at an angle e that ranges from 5° to 75° relative to the surface of skin at the area on which the topical composition was applied; and e. delivering the ultrasound to the area on which the topical composition was applied while maintaining the projection angle e that ranges from 5° to 75° relative to the surface of the skin at the area on which the topical composition was applied, wherein the topical composition comprises a hair growth or hair regrowth active benefit agent. (i) growing or regrowing hair on the skin and/or scalp; (ii) cleansing hair follicles and/or improving follicular delivery of active benefit agents; (iii) inducing micro-lesions on skin surface by means of cavitation bubbles to grow or regrow hair; or (iv) stimulating follicular stem cells to facilitate hair growth or regrowth, comprising the steps of: a. providing a topical composition for propagation of ultrasound waves from an ultrasound device ; b. applying the topical composition to an area of the skin or scalp in need of treatment; c. providing a device having power source and an acoustic transducer electrically connected to the power source, the transducer calibrated to generate acoustic energy at a frequency ranging from about 100 kHz to about 3000 kHz; d. orienting the device such that any ultrasound waves generated by the transducer are projected at an angle e that ranges from 5° to 75° relative to the surface of skin at the area on which the topical composition was applied; and e. delivering the ultrasound to the area on which the topical composition was applied while maintaining the projection angle e that ranges from 5° to 75° relative to the surface of the skin at the area on which the topical composition was applied, wherein the topical composition comprises a hair growth or hair regrowth active benefit agent. a. providing a topical composition for propagation of ultrasound waves from an ultrasound device ; b. applying the topical composition to an area of the skin or scalp in need of treatment; c. providing a device having power source and an acoustic transducer electrically connected to the power source, the transducer calibrated to generate acoustic energy at a frequency ranging from about 100 kHz to about 3000 kHz; d. orienting the device such that any ultrasound waves generated by the transducer are projected at an angle e that ranges from 5° to 75° relative to the surface of skin at the area on which the topical composition was applied; and e. delivering the ultrasound to the area on which the topical composition was applied while maintaining the projection angle e that ranges from 5° to 75° relative to the surface of the skin at the area on which the topical composition was applied, <EOS>