Abstract: A modulating light having a wavelength of 400 nm to 600 nm is irradiated to a portion around hair roots at an energy of 0.01 J/cm2 to 1 J/cm2 over a time period of not more than 1 ms as a flash light such that a light absorptive component existing in a human body around the hair roots absorbs the light for modulating hair growth without causing substantial adverse effect.

Abstract: A modulating light having a wavelength of 400 nm to 600 nm is irradiated to a portion around hair roots at an energy of 0.01 J/cm2 to 1 J/cm2 over a time period of not more than 1 ms as a flash light such that a light absorptive component existing in a human body around the hair roots absorbs the light for modulating hair growth without causing substantial adverse effect.

Abstract: An optical hair growth modulation device modulates hair growth by irradiating modulating light to skin. This device is provided with a modulating light irradiator for irradiating modulating light, a measuring light irradiator for irradiating measuring light for measurement of a target site of the human body to the target site, a light receiver for receiving the measuring light reflected from the target site, a processor for processing information of the measuring light received by the light receiver, and an irradiation determinator for judging whether or not to make the light irradiation from the modulating light irradiator based on a processing result of the processor. The irradiation determinator is configured to control irradiation of modulating light from the modulating light irradiator based on the judgment thereof.