No makeup product is either bad or bad for the skin. But there is a catch. Firstly, some people display allergic reactions to certain concealers. In that case the only option is to stop using that particular type of product. And if you use a concealer the way they are not supposed to be used, it can cause skin, even though temporary. The oils and other ingredients in concealers can block the pores in the skin. If you sleep without removing the makeup or wear it for too long, you will end up with bad acne. Using a concealer not meant for your skin type can also cause problems.