Some very good reply's on this, I have had the same problems as the OP, so here are my thoughts,
Always wipe the top of the bottle!!, never ever let the actual liquid contact the skin, it will burn and mark where ever it touches skin.
I have found the cheap shop brought poppers to be the worst offenders, also as soon as the poppers go past their best, the second they stop working, ditch them!, never try to make them last longer by having to inhale for longer periods, I find thats when they are most likely, almost guaranteed, to cause a bad cough, headaches and a general feeling of crappy ness, for days after.
One way I have used with success, to stop the red nose, is to use a card tube wrapped around the bottle, thus keeping the glass a small distance from the nose, or mouth, the card does not burn or mark!.
Some brands are just worse than others, and I think they can all make one cough for days after, if used too much, as in every day/night, or one very long session.
I love to use poppers when I am on my own, find them far more affective if I wait until I am very horny and almost ready to cum, in other words, its not the poppers that make me horny, so much as how much they enhance the experience when I am already horny.
Be very careful using poppers, when laid down, I once accidentally tipped a bottle, inhaling a good deal of the raw liquid, straight up my nose!!!, I was in a sauna, the pain was fantastic, in a very bad bad way!, I rushed to the toilet, trying to get as much fresh water up my nose as I could.
The pain lasted for days and days, my nose bled a bit, was incredibly sore, like getting a bad cold for days and days after, it literally took weeks to heel properly, I ended up visiting my doctor, to get some antibiotics, never told him it was the poppers though!.
I do not use them whilst laid down any more, well, not whilst laid on my back!!!.
I love poppers though, buy them online now, always wipe the top of the open bottle now, also good to keep a glass of water to hand, and some kitchen paper, in case any liquid does get into contact with the skin, wash the skin immediately, as in really fast!!, with the water, oh, and be careful with holding you're finger over the open bottle, to stop it evaporating, as you end up with an ugly stain on the finger.....
I think breathing poppers in through the mouth can be stronger and longer lasting than breathing through the nose, but maybe thats my imagination!.
I do miss the old formula, a large bottle of English could last me one month!!, now they are gone over within days, three days for most, can get a bit expensive, so best to have good breaks away from them, if only for you're wallets sake.....