I envy you: I used to have the full deal, but years of having to use a very strong sun blocker had the curious effect of killing off the sideburns. All that remains is the moustache bit, plus the stuff from the jawbone downwards. Actinic keratosis, sun damage, is the cause of the use of the cream.
I questioned the doc about the phenomenon, and she said that a fellow doc had mentioned the very same thing, and was thinking about starting some kind of investigation...
Moral: stay in the shade, and enjoy a gin and tonic.