The redness, burning etc (the 'hardening' effect - where your skin is adjusting to BP) is definitely a pain to go through but it should subside once you've stopped increasing the amount of BP you're using and have been at that point for a while. It is irritation but it will eventually go away. And it's also really important to then make sure you're being gentle in every other aspect of using the regimen to prevent further or direct irritation (e.g. when cleansing and applying BP / moisturiser etc)

Basically, BP works by killing acne bacteria and making the skin an environment that the acne causing bacteria can't live on through oxygenation of the skin. (I'm sure google will find a better answer somewhere )