When selecting your skin care products, there are two basic schools of thought – to stay brand loyal or to mix and match. And everyone does have their own opinions.
The short answer is to make the right choices based on your skin type and needs. If this means being brand-loyal because the entire regimen works for your skin, then by all means do so. But if your skin likes a cleanser from one brand and an eye cream from a different brand, then pick the ones that work for you.
If you are testing a new skincare brand, integrate only one new product at a time. If you change everything at once and experience a negative reaction, you will have no idea which one caused the reaction. But by strategically adding one at a time, you can better judge how your skin reacts and behaves to the new items.
Personally, I do think you can mix-and-match. Do be aware of the active ingredients in each product though. If you use a glycolic facial peel followed by a retinol cream, it could end up being too much for your skin. Likewise, topical vitamin C will neutralize certain ingredients such as copper peptide. In which case, you may not get the optimal results from either product.
This advice would also hold true for hair care, body care, and cosmetics. Oddly enough, most of us do not think twice about using one body wash and a different lotion. So the same can hold true for any of your products. In regards to cosmetics specifically, I do recommend that at least your foundation and concealer come from the same brand so that you end up with similar colors and undertones.