Headaches, sore throats, generally feeling a bit rubbish
Why it happens:
Dehydration is a cause of many an inflight irritation - the dry air of the cabin means you need to hydrate your body more than you would on the ground, or your body will feel it.
How to avoid it:
Drink water rather than alcohol both before you board and in the air - and lots of it. Slathering on the moisturiser will also help your skin look better when you get there.