Girls, Can I use my foundation as a concealer?

I was just wondering if it is ok to use my foundation as a concealer. It seems to me if you thin it out a little less, it could be used as a concealer. You can have it do double duty and not have to buy a separate concealer perhaps. Has anybody else done this? Did it workout alright? Thanks.

Girls, Can I use my foundation as a concealer?
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