Why do your ears pop or plug up after a head cold ?

Ears popping: The reason for the popping is that pressure builds up in the inner ear because there is inflammation around the eustacian tube. The eustacian tube helps let pressure out. Fluid build-up may also be contributing. Decongestants can help.

Eustachian tube: When you get a head cold, you get inflammation in your upper airways. This includes in the back of the nose. This is where the eustachian tube (et) empties out - the tube you usually use to pop your ears. With a cold, you can get fluid behind the ear drum which can't drain out through an inflamed et. Even without frank fluid, you can get abnormal pressure behind the drum that can't normalize.