How should "makeup" be written in BrEng?
Solution 1:
Apparently, Brits use the hyphenated and single-word versions about equally often...
...but Americans have more decisively abandoned the hyphen...
In such usages the general trend is always two words -> hyphenated -> single word, so I've no doubt UK usage will catch up soon enough. As of right now I would say both forms are equally "valid" in BrE - but you may as well dump the hyphen now, since we all will eventually.