Experts explain why some seem to stop working—and what you can do about it.

By Lisa Whitmore
Updated January 14, 2011
Craig Cutler

You’ve probably experienced it: A once magical lotion or shampoo—poof!—starts to lose its magic. Has the product changed, or is it just your (overactive) imagination?

The Probable Explanations

Possibility number one: You’ve changed your application habits. “People use a product diligently in the beginning,” says April Armstrong, an assistant professor of dermatology at the University of California, Davis. “However, compliance decreases over time.” And when you don’t apply, say, an anti-aging serum or an acne lotion consistently, results can slow. Possibility number two: You’ve been using a particular product for too long. For example, silicone hair products can build up, causing hair fibers to react differently to them after a while, according to Carmine Minardi, a co-owner of the Minardi Salon, in New York City. Other possibilities: “Changes in diet, climate, and your hormones may subtly affect the way a product responds,” says Ni’Kita Wilson, a cosmetic chemist in Fairfield, New Jersey. So the oil-free moisturizer that did the job in humid summer months may not offer enough hydration come dry, windy winter. Less common factors, like differences in product batches and shelf lives, can come into play, too. A final possibility: You’ve become so used to the product—its smell, how it feels on your skin—that you’re not as excited by it anymore, which can make it seem less effective.

Exceptions to the Rules

There are a few instances when you may truly become resistant to a particular ingredient. “Some topical steroids, which you use for skin irritations and conditions like eczema, may lose efficacy over time,” says Armstrong. The benefits of retinol and benzoyl peroxide can also level off. It’s not that they’re not performing as well; rather, the fine lines and acne that these ingredients treat have improved, so further changes seem less dramatic. With time, antidandruff shampoos, too, can lose strength, but Armstrong says there’s no medical consensus as to why.

How to Keep Seeing Results

First make sure that you’re using the product exactly as directed and that if there is an expiration date, it hasn’t passed (ingredients can start to degrade after the use-by date; exposure to light can also reduce products’ efficacy). Unfortunately, there’s not much you can do about batch-to-batch discrepancies. For silicone buildup on hair, which can make strands look dull and feel heavy, “try a clarifying shampoo once every 5 to 10 washes,” says Minardi. If you’re applying an anti-aging, acne, or antidandruff product, consider switching it up. For example, if you’re using an over-the-counter version, see a dermatologist for a prescription formula, or change the brand to keep results coming. Finally, ask yourself whether the product has achieved what it was supposed to. You may have reached a point where any further improvement is so subtle, it’s almost impossible to detect. “Managing your expectations is key,” says Armstrong.