Answers (1)
Some chemicals absorb light of one wavelength and reradiate it as light of a different wavelength. That is called fluorescence. The light of interest is ultraviolet, but the same effect happens at other wavelengths.
Some chemicals in the body fluoresce. That is all you are seeing.
BTW don't look directly at the black light source. The human eye can not limit ultraviolet light the way it limits visible light, and you can burn your eyes.
I'm speaking in general terms. I have no knowledge about your face.
but about a month before it didn't show those spots on my face in a black light