During my most recent visit with my rheumatologist he asked if I used the disposable heat packs in my shoes.
I replied "of course" (though in my slippers as I rarely get into shoes, it has been a harsh winter.) I also mentioned that on two rare occasions they became so hot I removed them and let them expire on a heat safe surface.
He said he mentioned it because he has 2 other sclero clients with difficult ulcers on their feet due overheating disposable heat packs.
I am heeding his warning though; I am also fortunate enough at the moment to realize IF they get too hot.