Most of what people know about sunscreen comes from the back of a bottle, and that's part of the problem. SPF has been reduced to a number you glance at while shopping, when it actually represents one of the only skincare interventions with decades of clinical evidence behind it. If you've invested in facials, peels, or laser treatments but skip sunscreen most days, you're working against your own results. Here's what's actually happening beneath the surface, and why this one habit outperforms nearly everything else in a skincare routine.