sauna skin

Hi,

I have recently started dry brushing my skin. Haven't noticed any big benefits yet, but I'm still new. However, I notice that when I take a sauna/steam if I rub my skin big globs of black yukky dirt comes off (espcially if I scratch it with my nails).

It seems as though it's never ending - there is so much of this stuff!!!

What is this stuff? And should it lessen with more skin brushing. Or, can you brush your skin too much (obvious signs apart, like I'm not causing abrasions or soreness)?

Thanks,
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