Hi everyone

This may be a little bit of an odd one. I have noticed that I have had small oil / grease looking stains where my nipples / areola meets the bra cup on beige / light beige bras. Not everyone of them but I wonder if it is because I haven't noticed them and thrown them in the wash. I don't think I am having nipple discharge as I don't have a discharge when I squeeze. I am wondering if anyone other women have noticed this?

Is this oil/sweat from the areola / nipple? Anyone else noticed this and have any idea what it is. I am starting to worry and I don't want to. Thank you to anyone who replies in advance!