Has he seen the doc and had blood tests to rule out any underlying cause?
If so it's probably just one of those things, it's quite common as we get older apparently :(. My friend's mum has it and despite all the tests no reason has been found. I don't think anti bacterial products are good though, they may be a bit harsh. There are lots of gentle, unperfumed moisturising products these days, I'm sure someone will recommend something.
Could he take a non drowsy antihistamine to see if that helps?