under arm stains

You feel like you haven’t had the shirt very long or at least you haven’t worn it that many times before you notice that slight discoloration, sort of a yellowish hue, underneath the arms.  What is it?  Perspiration.  Actually, it is likely a combination of perspiration and anti-perspirant, and while that discoloring can form on other areas of your garments, it seems the most vulnerable area is under the arms.