Even with a teeny dose, there is still a chance your skin could react to a certain active, be it from the potency or an allergy to the ingredient itself. That said, you should still patch test a product before slathering it on—even if it does contain 1/10 its usual power. “There’s also the risk of micro-dosing multiple products with the same active ingredient, which can bring you right back to square one,” warns Rodney. Translation: Micro concentrations do not give you permission to layer on serum after serum.
And for those without sensitive-skin concerns, “I look at micro-dosing as a gateway to your full skin care routine,” Zeichner says. “The goal is to eventually transition yourself to a full concentration.” Of course, “full concentration” has a different definition for everyone; the point is, you might want to use micro-dosing as a way to investigate how much your skin can truly handle, increasing or decreasing the dosage until you find a happy medium. Because just as you don’t want to overwhelm your skin with too-potent formulas, you also want to make sure your regimen, well, actually works.
Lastly (and this probably goes without saying), both Rodney and Zeichner emphasize: Don’t micro-dose your sunscreen. You still need about a nickel-size dollop for your entire face, reapplying every two hours for optimal protection.