It’s the worst kind of surprise: Out of nowhere, your skin flares up with itchiness, redness, or bumps. The irritation sends you on a crazy detective hunt to track down what caused the allergy attack—was it your face wash, moisturizer, foundation, blush, or night cream? The trigger is tricky to determine, yet skin allergies to ingredients that are in most cosmetics are shockingly common. So we called up Dr. Noëlle Sherber, a dermatologist in Washington, D.C., to break down what’s making your skin so upset, how to fix it now, and ways to prevent it from happening again.