So many people have acne problems ( as do I )and as some things work for some people, those same things may not work for others.
If you have the money, and are NOT allergic to sulphur, you could try the one advertised on TV. I've heard many people rave about it, but for those of us who have allergies, this is not a good choice.
Tightening of the skin is actually a good thing...it means the pores are being tightened, which in turn means that the blackheads will go away.
The stinging to a degree, is normal...after all, it grapefruit is acidic.
In many countries the rinds or peels of highly acidic fruits have been used for centuries.
There are many products out there that claim to help...but they don't work for everyone. One may work great for Jon, but might make Sue's worse.
It's one of those hit and miss sort of things.
Your best action is to see a dermatologist, but if you have hereditary acne ( which many people do ) even a dermatologist may not be able to help.
Personally, I find that taking a shower every night and using ONLY baby shampoo to wash with has helped greatly. ( If you can't shower/bathe every day due to circumstances such as eczema, you can use a hot compress on your face followed by a cold one.)
Many claim that you need to use a lotion or cream every day/night...but these can clog the pores even more. By taking a hot shower or bath, you are steaming the pores open. After your shower/bath you can use a cold face cloth to close and tighten the pores.
I hope at least some of this has helped.