[Acne] How exactly does irritation and certain products cause breakouts if acne is really an issue with clogged pores and bacteria?

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Can someone help me understand why and how the wrong product or ingredient breaks only some people out - same for "irritation" (whatever that means??) because it just sounds some maxim people here spit out but don't explain.Also I have been using Cerave cleansers and I think it broke me out. At first I couldn't tell because I was on Stridex, but I got acne on my chest which I never have before. Does that mean breakout?
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Submitted by 2k16throwaway