Developing a skincare routine personalized to your needs takes a lot of trial and error — which is why when you’ve found your signature serums, moisturizers and eye creams, you may be tempted to stick with them for life. But as with anything in life, our skin can change, and certain products can stop having the same glow-inducing, anti-aging, acne-fighting effects they once had. We asked board-certified and celebrity dermatologist Dr. Paul Jarrod Frank if your skin can get used to products, what to do if that’s the case and how to prevent this from happening.Why do skincare products stop working?“They don’t stop working per se; our skin just becomes acclimated to them, or our skin needs change,” Dr. Frank says. “As we get older our skin becomes drier, we start to see more fine lines and brown spots, so it is important to adapt to our changing skin.” Think of the acne cleanser you used as a teen or the lightweight moisturizer you reach for in the summer — you might not use the cleanser into your twenties and beyond, and you likely switch to a richer cream in the winter.How can you tell if your skin is getting used to a product?“The best example is using retinol,” Dr. Frank says. Retinol is an extremely potent ingredient that can target signs of aging, sun damage and acne. While it’s often lauded for its effectiveness, it can take your skin awhile to get adjusted to. When you’re first starting out with retinol, your skin may become dry, red, itchy and irritated. “Typically, we start out slowly with a low concentration and increase the usage. Once the redness and flakiness stops when using it nightly, it might be time to up the ante and increase the concentration.” We recommend starting with the CeraVe Skin Renewing Retinol Serum, a low-dose concentration combined with hyaluronic acid to restore moisture. If your skin is getting used to an active ingredient, it’s usually safe to increase the concentration, Dr. Frank says. “The percentage of active ingredients should be increased with tolerance, but you must increase slowly, like you did in the beginning.”How can you prevent your skin from getting used to a product?Take a break, especially from active ingredients. “If you’re maxed out on your retinol, stop for a week or two and start back up again,” Dr. Frank says. Is being used to a product ever a good thing?“If your skin isn’t irritated and you feel sufficiently hydrated, chances are the products you are using are working,” Dr. Frank says. “It doesn’t mean the products are less effective — they simply might be providing the balance your skin needs. As the saying goes, if it ain’t broke, don’t fix it!” Photo: Chaunte VaughnRead More:The Best Skincare Products That Contain AHAs or BHAs, According to Our EditorsSo, You Popped a Pimple — Here’s What to Do Next and How to Heal ItHydrating vs. Moisturizing: What’s the Difference?