Why does only one nostril feel blocked at a time?

Even when you’re not sick, you don’t breathe evenly through both nostrils — your zenuwstelsel (nervous system) quietly sends extra blood to one neusgat (nostril) at a time, swelling its tissue slightly so more air flows through the other. This is de nasale cyclus, the nasal cycle, and it switches sides roughly every one to two hours, sick or not, without you ever noticing.

When you catch a cold, the cycle doesn’t change — it just gets exaggerated. Your immune system pumps extra blood into whichever nostril is already swollen, so the effect that normally goes unnoticed becomes a fully blocked neusgat. Neusgat itself is a plain compound: neus (“nose”) plus gat (“hole”) — the same blunt, literal pattern Dutch uses for a lot of body parts.