I have very sensative skin..what causes big round discolored marks under my arms?

i have had the same experience, try using some aloe under your arm to heal the scars

Try using Dove deodorants formulated for sensitive skin.The marks are the scars left over from the burning rash that you had. I also have very sensitive skin,clinically-diagnosed sensitive skin since I have atopic dermatitis.You need to try different sensitive skin formulations until you find one that doesn't irritate your skin. And just because it's "all-natural" means it's okay for sensitive skin;"all-natural" doesn't mean non-irritating.Another thing to watch out for are the words "hypo-allergenic".My dermatologist told me that those words are not a guarantee that an allergic reaction won't happen. You need to look for unscented products also,because the scented products are irritating to sensitive skin.

My husband had this EXACT thing. Stop using anything with the anti-persperant in it. Find one that is deodorant only. Something about the antip causes an irritation and burn. That scar will not go away. It will fade some though. The person before me said it...It's left from the burn the rash caused. Good Luck I hope that helps some.