Preface: Feel free to skip the long background story... actual question is at the end (in bold).
I've had mild-to-moderate acne generally well controlled with benzoyl peroxide and, more recently, adapalene (Differin). About two months ago, I started to break out horribly across my jaw... probably a combination of getting lackadaisical with my skin care routine, running out of Differin, getting super stressed about exams, etc. Anyway, I freaked (naturally) and I found this forum. I thought I'd give the vaunted Regimen a try, with the Philosophy Hope in a Jar moisturizer (new product #1). I saw the Philosophy primer (The Present) while I was at Sephora and decided to give that a try too (new product #2). Just to be on the safe side, I also went to my family doc to get my script for Differin renewed... and while I was there, I decided to ask about Tactuo (adapalene-benzoyl peroxide; Epiduo), which seemed legit from the clinical studies and user reviews. Also, why not? I'd used adapalene and benzoyl peroxide before... what could possibly go wrong? So my family doc gave my some samples of the Tactuo and off I went with that (new product #3).
As luck would have it, my jaw got worse and, within about 7 or 8 days, my cheeks started to swell and I developed these crazy vesicles and pustules on my cheeks that wept and crusted. Then I started to get these small erosions/ulcers within those areas. Hideous, right? Anyway, after seeing a whole bunch of different doctors, the consensus seemed to be that it was a contact reaction to one of the new products I was using. Which product? Well, because I'm a genius and I started three new products all at the same time, I'll never know. To be fair, though, I don't have any allergies and I've never had any problems with anything I've put on my skin... and I've used tons of over-the-counter acne treatments, prescription topical acne treatments, and cosmetics.
Right now, I'm doing OK with doxycycline and PhisoHex, but (a) I still have a few whiteheads/pustules and (b) I really don't want to using either one forever. At the same time, I'm too scared to start/restart anything containing adapalene and/or benzoyl peroxide. So my question to you is... how do you go about trying new products (e.g., do you patch test, where do you test, for how long do you patch test before letting yourself use it more extensively, etc.)