Foundation primers are seen in many makeup artistry lines, such as Laura Mercier, Vincent Longo, and NARS. Basically, these “primers” are nothing more than lightweight, silicone-based moisturizers. The silicone allows the product to spread easily over the skin, and to some extent can help smooth the skin’s texture and remedy mild dry patches that could spell trouble when you apply most types of foundation. These primers also tend to have a soft matte finish on the skin once they dry down, and that can make your foundation a bit easier to control and blend because the skin will be much less slippery than if you had applied an emollient moisturizer.
Still, primers are truly optional and their benefits do not outweigh the extra step and expense. The only reason to consider one is if you have normal to oily skin and need the extra smoothness these can provide in order to make your foundation look its best. It is best to test these out via sampling before investing in a full-size tube so you can be sure you’re making the purchase because you like what it does for your skin—not because you get suckered into the marketing pitch that makes it sound so important for skin. One more point: Lots of brilliantly formulated serums offer the same benefits as a foundation primer, but with the added bonus of giving your skin some truly helpful ingredients. In contrast, most foundation primer formulas lack these bells and whistles—and you definitely don’t need a serum and a foundation primer!
Eyeshadow primers are sold to the consumer to help eyeshadows stay in place longer. The eye area is indeed a tricky place to get color to last, but there are ways to make it stay without specialty products. Besides, most eyeshadow bases are very similar to cream-to-powder concealers or foundations. Placing a matte or semi-matte foundation or concealer on your eyelid and applying loose powder over it works just as well. Also, if your eyeshadows tend to smear or slip into the eyelid crease, you can greatly reduce the problem by not placing a moisturizer or greasy foundation on your eyelid.