How to use SPF

SPF stands for Sun Protection Factor. The number tells you roughly how much longer your skin can stay in the sun before it starts to burn, compared to wearing nothing. It's worth knowing that SPF mostly tracks one type of UV, the kind that burns the surface (UVB). It doesn't tell you much about the deeper rays (UVA) that affect skin firmness and structure over time, so the word to look for on the label is "broad-spectrum," which means it covers both.

A higher SPF number isn't double the protection. SPF relates more to time and how completely you cover your skin than to a simple multiplier.

Picking and applying it

• Go broad-spectrum, around SPF 30. That's a sensible everyday range for most people; higher is fine if you burn easily or you're out for a long stretch.
• Use enough. Most of us apply far too little. A rough guide is about a quarter teaspoon for the face and neck. Skimping is the most common reason sunscreen underperforms.
• Most formulas work right away, mineral ones especially, so you don't have to wait long before heading out. Applying before you leave is the simplest habit.
• Reapply through the day. No sunscreen lasts all day. It wears off with sweat, water, towels, and time, so topping up every couple of hours outdoors helps.

Winter and cloudy days count too

UV doesn't take the colder months off. UVA passes through clouds and windows, and snow and altitude can actually raise your exposure. Daily protection through winter is the same idea as summer, just easy to forget.

Sunscreen is one tool, not the only one. Shade, a hat, sunglasses, and clothing all add up, and a tan isn't a sign of healthy or protected skin. If you have a spot that's changing, growing, or behaving oddly, that's worth getting checked by a professional.