Prickly heat on feet when running

I have been running for just about a year, having started at
age 52 as part of a mullti-faceted weight reduction effort.
I always wanted to run despite being relatively slow, I like
the feeling after a nice run. Now as the hotter weather is
upon us in Kansas, I've begun to notice that about two miles
into a 30 minute run I get a feeling I can only describe as
prickly heat on the bottom of my feet. Having read that the
tingling feeling might be an indicator of worn out shoes, I
replaced a a pair of New Balance 470 (department store
grade) running shows with a pair of brooks Trance NXG with
Sof Sole inserts for those of us who over protinate on
mildly flat feet. I've put about 8 miles on the new shoes
and still have the same effect. The obvious reason is: hey
stupid it's hot outside and nothing builds heat faster than
a sweaty foot stuffed into a running shoe. Prickly heat
feeling disappears after I stop running, and there's been no
long term effect.

I just thought I'd see if there's any other reasons. I'd
like to prevent any further injuries from occurring. Thanks.

Greg Crawford - Kansas