[vvv]

I don't have much chem background beyond first year uni which I don't remember anything from, so how can acne medications mix these two chemicals when one is basic and the other acidic -- wouldn't they just neutralize each other?

I thought about this when I mixed some 10% benzoyl peroxide lotion with my regular non-comedogenic moisturizer (nothing to do with salicylic acid) to make a 2.5% blend and noticed it formed small curds that weren't present in either mixture alone. I figured the basic benzoyl peroxide probably screwed something up in the moisturizer... without any real quantitative tests or knowledge of exactly what's in each (I could look up the ingredients but I'm assuming there are some common ingredients in pretty much all moisturizers), does this even make sense, and should I be concerned that the effectiveness of the benzoyl peroxide and/or moisturizer was reduced?  It seems common practice to apply moisturizer and then apply acne medication and vice versa, so this could be a pretty common problem that people should know about...

Thanks!

[nj_bartel]

Neutralize is an acid/base reaction.  The acidic/basic functionalities of the drugs aren't the elements of the drugs that make them biologically active.

[vvv]

I suppose the non H+ side of salicylic acid probably is the functional side of salicylic acid, but BP works by releasing oxygen (the acne bacteria can't survive in a high oxygen environment), which combines with any free H+ from any acid to form H2O in the neutralization reaction, no?

[nj_bartel]

If I had to guess (I don't actually know, just to be clear), I would think the mechanism for BP would be formation of highly reactive radical species. BP is frequently used as an initiator in radical reactions (homolyzes between the peroxide bond)