Having freckly/fair skin I need to wear sunscreen every day. Some brands can leave a yellow/brown stain on light clothes. To remove this stain: moisten the area, rub with plenty of dishwashing liquid (I use a popular clear green type), and scrub with a nail brush if the fabric can take it.
Thanks for the great tip. I have just changed to a Coppertone kids product and it wasn't until I did a white wash that I found 4 of my daughters white tops essentially ruined by yellow stains. I followed your tip with regular dishwashing liquid with an old toothbrush and this morning 2 are back to normal and the other 2 are much improved. Thanks heaps, you've saved me from throwing them all away!
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After reading all the comments about chemical reactions I decided to do a little experimenting myself. I found that The Works tub & shower cleaner takes out the stain.