I've always had white sheets on my bed. After awhile, no matter the thread count, the middle part of the fitted sheet (the stretchy bottom one), turns kinda blue-ish.

I've had lower thread count sheets (300 TC from JCPenney) and higher thread count sheets (500 TC from Dillards) do this. So I don't think it's a quality issue.

I swear I don't sweat blue. Is it just from wear? I move around a lot when I sleep, so I'd think the wear would be more spread out across the whole width...

Any ideas why this happens, or how to fix/prevent it?

Is there a logo/tag on your mattress in the spot where it turns blue? It's possible that the ink is bleeding. Or it could be from a lotion/body product you're using.

There are a lot of blue mattresses - is yours blue? If so, I'd get a mattress cover and some bleach for those sheets.

Do you wear a lot of super dark wash jeans? You may not notice the blue on your legs, but it will definitely show on white sheets.

I second the dark wash/not super expensive wash jeans. Sometimes if I wear new blue jeans they turn my toilet seat blue from staining my thighs.

You can't pay me to have white sheets on my bed. The slightest stain would drive me insane. White sheets also remind me of hospitals. Dark sheets don't show those kinds of stains and you also don't have to wash them with bleach which is toxic. And now you have an excuse to go buy new fun sheets!

Same here, although for different reasons. I love the idea of having the type of home where I could have crisp, white sheets on my beds, but alas, having 7 furballs doesn't combine well with...well, anything white. Oh well.

Penmage, I'm also curious if you wear anything blueish (jeans? pajamas?) in the bed regularly. My blue washing detergent stains things on occasion if it drips directly onto a shirt, but that wouldn't explain why you're getting such a big area just in the middle of your bed. Very puzzling.

Thanks for the suggestions, guys!

Wannabeskinny- Oh, darn, looks like I'll have to go shopping. lol
LovesToTravel- not particularly. I usually sleep in a long shirt unless it's cold out, but my pajama pants aren't dark anyway. Although I'd be impressed if my pink heart pajama pants could create a giant blue area on my sheet!

My mattress is all white, even the little logo thingy. My comforter is black and white and gray, so I might have to get some gray sheets

I don't know if this is what's going on with your sheets but I have had both clothes and white pillowcases get large blue spots from two things, liquid fabric softeners and lately from clorox two colorsafe bleach