I don't know if it'll irritate it.

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There's nothing wrong with using a bit of concealer or foundation to camouflage or hide the odd spot…however I do think they’re 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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It depends on the type of make-up or the person if it'll irriate the skin, so thats not a question that can be answered and be 100% true…but as far as aesthetics..it doesn't look very great…but there’s a compact from MAC called studio finish..it is a mixture of both a powder and foundation concealer. you can buy it online but I think it's a superior idea to go to a MAC store to find out what color you would need

(to go along with what someone stated about an oil-e-r face…the compact actually absorbs the oil on your face!!!)

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Not really sure what I would suggest to you. Its difficult to pick so what I end up doing is starting with the less expensive and trying out several products.This is a good review website at http://www.brandsmakeup.com visit and read the reviews.
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it will irritate the skin, i think you should treat those problems with good face wash, exfoliator and a moisturizer and not trying to cover it up.
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don’t put it on cold sores. it will spread them and make them last longer.

i suggest abreva it expensive but it works wonders.

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I imagine it's bad for cold sores and if the foundation isn't meant to treat acne, it won't be good for acne.
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Its totally okay! It might your skin a little bit more oily but just make sure to wash your face each day!