Perforated Nasal Septum
The septum is the wall separating the right nostril from the left. Snorting cocaine or methamphetamine damages the septum by cutting off its blood supply. Bit by bit, the septum wears away, until there’s a hole. Then, whenever you breathe through the nose, wasted air goes from one side to the other. So you feel like there’s congestion.
Once there’s a hole, the only treatment is surgery. Prevention is a lot better (a good reason not to snort).
Deviated Nasal Septum (+ Allergy)
In some people, the septum is pushed to one side, maybe from birth, more likely from an old injury. Then, if the nose becomes just a little congested from allergies, it feels a lot worse because it’s harder to breathe through the narrower side.
There’s no danger to this, but it can certainly be uncomfortable. Allergy Medicines can help. An Ear-Nose-Throat (ENT) specialist can try surgery, but many people with deviated septums don’t want to go through with it (it’s not a necessary procedure).