I have written before about how I don’t think that there is very much value in the comedogenic scale that attempts to rate cosmetic ingredient for their potential to cause blackheads.  But this rather begs the question, posed to me by Livvi on Twitter,  what ingredients do cause them?   Livvi actually asked what ingredients block pores – but although blocking pores doesn’t automatically mean blackheads, that is the main problem. Phew, this is a bit of a tough one. Continue reading →