Hello,

I've got white, streaking stains under both side mirrors (see picture). Car wash, hand wash, even gentle scrubbing won't remove. I haven't tried anything but soap, yet...

Can anyone identify what the stain is, and how I might remove it?

We get nasty winters where I live so it could be salt. The car is almost 6 years old.

Thanks for reading.

Looks like salty water from the road got trapped and dried. Now its melting and running down your door.
If you get a decent clay bar kit, you can probably get rid of the embedded stain.

Wax also gets trapped in spots like that. Carefully try to wash it off, it may just be waxy buildup which ran down with rainwater onto your paint.

Unfortunately it looks like it may recur, occasionally.

Get yourself a clay bar and some compound it will take that right off. I have dealt with many cases like this and it is really simple to take care of.

I agree with 99FBOY, you'll defintely need a compound to take care of this, a heavy compound will do the trick but go for a weaker one if it's your first time using a compound. You need to wipe the area down clean, then use the compound (the same way you use wax), wash the compound off then wax and polish...you should be good.