toddler rash - ideas?

Ds (27 mo) has a rash under his chin, extending from the chin to midway
down the neck. It's more pronounced on his right side. It is completely
colourless, just a rough bumpiness on the skin, and appears to be
mildly itchy; he doesn't generally scratch it during the day, but when
he's at rest and especially in the evenings before bed and in the
morning when he first wakes up, it seems to be bothering him and he
rubs at it vigorously.

Dh has suggested washing more with soap (I generally just use a clean,
wet cloth to wash his face and neck), but I'm hesitant b/c it can be so
drying. When the itching gets bad, I use a small amount of Aveeno
anti-itch lotion, which seems to help.

Any ideas as to what's causing it? It isn't anywhere that clothing
touches normally, and we haven't changed soaps or detergents lately. In
the past he has developed red itchy rashes around his mouth and on his
cheeks, which seem to be caused either by too much sugar or by red food
dye (crops out around Christmas and other candy-heavy holidays when
relatives are giving him sweets left right and centre). This, however,
seems different, given that it's not red at all and is restricted to
the lower chin and neck. It's been coming and going for a few months
now without any clear correlation to environmental influences.

Any suggestions for both cause and treatments would be greatly
appreciated - I am planning on taking him to his doctor about it, but
I'm not holding out for much insight there, to be brutally honest (not
an opinion about docs generally, just about this one!).

TIA,
Melania
Mom to Joffre (Jan 11, 2003)
and #2 (edd May 21, 2005)