Cotton Buds for the Ears- Takeoff

[flapsforty]

Joles, someone with a medical background can explain it better, but for now try this.

When you go up in the air, the air gets thinner and the pressure gets lower. Modern aircraft are pressure cabins, which means that they pressurise the cabin air to make flying more comfortable for us humans, and to keep the oxygen content in the air high enough for us.
Thing is, the pressure does not stay quite as high as it does on the ground. It becomes something like what you get high in the mountains.
So during take off, the pressure becomes lower than it was before you took off.

Your eardrum is between the air in the aircraft and the air inside your body. So those 2 pressures need to be the same, otherwise it gets uncomfortable or worse.
The eardrum is in between the external auditorial channel and the eustachian tube, as you can see in the picture.
Now the air in the channel lower right away, its a 'direct outside line'. The air in the tube (number 9 in the pic) takes a bit longer. The tube connects to the back of the throat, and via the mouth and nose to the outside air. If you swallow or yawn you ease the equalisation of the pressure.
If you have cold, the tube gets stuffed and it becomes harder or impossible to equalise. Which is when you can either 'steam' before a flight or use nosedrops to unblock your tubes 20 mins beofre take-off or descent..

other pic

Hope this helps, and if it doesn't, ask someone who is medically qualified for a better explanation.