http://www.acne-web.org/cold-sore-acne/
Is it bad to use liquid foundation to cover up acne or cold sores?
I don’t know if it’ll irritate it.
There’s nothing wrong with using a bit of concealer or foundation to camouflage or hide the odd spot…however I do think they are best left untouched!! makeup will clog your pores and therefore irritate your skin further…but it honestly is up to you, if you do put makeup on your skin just make sure you wipe it off properly before you sleep to prevent further break outs. I would leave the cold sore alone though and apply only a cold sore cream to the area it should hopefully go within a few days 
goodluck hun
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