"When chemists mix multiple ingredients together, usually each individual ingredient is not as active," says board-certified dermatologist Morgan Rabach, MD. She explains that certain actives—like vitamin C, which is highly unstable—need to be mixed in a specific way in order to make sure that they won't break down. When any sort of deterioration happens, the ingredient won't be able to work to its full potential, meaning your skin won't be getting quite as much out of it.
In addition to messing with the actives themselves, combining certain ingredients in a single formula can also mess with your skin. "I would avoid pairing vitamin C, alpha- and beta-hydroxy acids, and retinols together because they are all irritating," says Dr. Rabach. (FWIW: You do always want to look for vitamin C paired with vitamin E and ferulic acid, because it makes the ingredient more stable).
Instead, she suggests sticking with single-active ingredient serums instead of more complicated ones in almost all situations, and other derms co-sign this. "Sometimes serums can contain more than one active ingredient and be okay, but the way the formulation is made, it can cause irritation or cause an ingredient not to be as effective as if it were alone," says board-certified dermatologist Shari Sperling, MD. To be clear, the term "single-ingredient skin care" doesn't mean that each bottle contains only one ingredient, but rather that it's only got one active working its magic on your skin. The product may be supplemented with other things, like water, oil, and hydrators, in order to make it useable.
As far as which single-active products you should be using in your routine (aside from a cleanser and moisturizer), derms recommend an antioxidant, a hydrator, an exfoliant, and a retinol. Below, our picks in each category worth stocking your shelves with—and you can snag all four for under $60 (much less than what you'd be paying for one of those "miracle mixes," anyway).
Antioxidant: The Ordinary Vitamin C Suspension 30% in Silicone, $7
It's important to apply an antioxidant every morning to protect your skin from pollution (which causes free-radical damage that leads to aging), and vitamin C is the best in the business. This serum has a 30 percent concentration of pure L-ascorbic acid, which is suspended in silicone to keep it from irritating skin and allow it to go on smoothly.
Exfoliant: Pixi Glow Tonic, $15
With a five percent concentration of BHA, this toner chemically sloughs away dead, dry cells, helps even skin tone, and reduces the appearance of large pores. Integrate it into your evening routine up to two times a week, and follow up with hyaluronic acid and moisturizer.
Retinol: The Inkey List Retinol Anti-Aging Serum, $10
The Inkey List built its brand on launching affordable and effective single-active products, and its latest retinol is exactly that. It's got 1.5 percent of the active ingredient, and works to stimulate cell turnover in order to reduce the appearance of uneven texture, fine lines, and wrinkles. Be sure to use your retinol only on nights when you aren't using your exfoliating acid, as the two together will likely irritate your skin.
Think of your hyaluronic acid serum as a sponge for your skin. It can hold 1,000 times its weight in water, which means when you apply it ahead of your moisturizer it will help it penetrate into your skin more deeply for added hydration. This much-hyped drugstore product is beloved by dermatologists and consumers alike (a bottle of the stuff sells every minute in the U.S.), because it combines short and long-chain HA molecules, which work to instantly plump the skin and hydrate it over time. Apply it morning and night, after your other serums and before your moisturizer, for best results.
Loading More Posts...