my mother is 91 & we have noticed that her shirts are turning yellow from sweat stains all over ie, on the sleeves & down the front of her shirt. arms pits are not yellow though... it is a very distictive yellow color & nothing with remove it...she is generally healthy , but doesnt drink a lot of water, could this be the problem.?.. also she is a nervous person & her diet could be better , doesnt want to eat real healthy. otehr wise she has no medical conditions, no heart issues or on any medication for anything..