4% BHA.

"The 4% BHA is a well formulated product, I'm not saying it's not. Paula's Choice knows what they're doing, and the adenosine and glycerin additions show they thought about the irritation potential, that's actually smart formulating. But for melanin rich skin, the risk benefit calculation is different than it is for someone else. Do not touch the 4% if your main concern is active breakouts or acne, the 2% was specifically formulated for that and the 4% wasn't. If you currently have active hyperpigmentation or dark marks, please do not jump to a higher acid concentration, you need your barrier stable and calm to fade existing marks, irritation will set you back, not move you forward. The 4% might be worth considering only if you have sensitive or reactive skin and you've been using the 2% consistently for at least six months with zero irritation, you've genuinely plateaued on texture and congestion, and your concerns are about refinement and anti-aging rather than reactive breakouts, and even then you should ease in two or three times a week and watch for new sensitivity or dark marks."