Thought I would give some info here as I battled with my knuckled for YEARS! and a lot of trials and error and I know what works for me. I was part of SCT years ago on a diff account but now I am re-lightening my skin as my hands are...getting better. Here's my progress pics to show...
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What destroyed it? Chemical peels lol, that thing is the devil if you do too much
Anyway here's my regimen
The ordinary 30% AHA/BHA acid 2x a day (morning and night) - its gentle, but if used 2x a day everyday for 10mins each time, it'll micro-peel within a week without causing PIH.
ALSO previously pink peeling oil worked for me - I got it from Rixari but idk where else to find it, I did 2x a day for 2 days and it did the same job - I redid again 2 weeks after healing
Hydroquinone (etsy, ebay is your friend if you're in UK) - the very thing that causes the issue for some people. I applied this 2x a day (mixed with 0.5% tretinoin I got from Spain) and did this after the peeling treatment everyday. You said no HQ...so maybe Alpha arbutin will help but it will be MUCH slower!
This took me....1.5-2 months? I am still working on it, its not perfect but the sun can take you back to square 1 in one second (summer time is hard!!).
I made the ugly mistake of using 60% GA on my knuckled (I ran out of the ordinary peel) and it made my hands a little darker!!! so now I'm reusing the ordinary again to get my hands back.
So I wear UPF50+ hand gloves (fingerless) during the day, I get strange looks from people sometimes but I had stranger looks when my hands were the before pic so, choose your devil.
This might work on you, or not. Hopefully it does! Now I am working on my body - I was a NC44.4 last year (LOVED IT) but my body wasn't even, so I took a break and redarkened. Now I'm using GA/LA 17% lotion to exfoliate before I start my lightening journey again.