Will triamcinolon acetonide cream help the yeast infection I have under my breast I was given powder but had an allergic reaction to it?

Temporarily. Cortisone cream may subdue the inflammation caused by the yeast infection but would not eradicate it (in fact may potentially worsen it). You need to keep the area dry by using antiperspirant regularly to discourage fungal growth. An antifungal cream for a few days will usually eradicate the problem.