If you haven’t yet had a chance to watch it, the November 23rd episode of Chuck Lorre’s _Two and a Half Men_ has a scene with Alan spraying on a fictional “Captain Terry’s Spray on Hair”, taking some untested hair growth pill and going on J-Date. These are all things I have done in my life and I found it particularly amusing. It’s interesting that they wrote this in since Jon Cryer seems to use some kind of concealer in real life. His hair looks too thick on screen.
Of course, I suspect a lot of actors use concealers, even the ones who do not have balding.
You’re not alone. Tabloid site TMZ did a quick double take on Jon Cryer’s hair situation about a year ago — see here. He could very well be using a product in his hair, or perhaps the producers of the show have him do it to maintain consistency or youthfulness in the character. There does appear to be something going on with his hair, but I really don’t know for sure.
And yes, I’d guess that your suspicion is correct about many actors using concealers. A youthful look is something many people strive for, and of course those celebs have many reasons to look their best.