I laughed when I first heard someone say you should wear sunscreen indoors. It sounded like something a skincare influencer would say to sell products. Then a dermatologist explained the science and I stopped laughing.

The Window Problem

Glass blocks UVB rays — the ones that burn you. But it does not block UVA rays, which penetrate deeper into your skin and cause aging and contribute to skin cancer risk. If you sit next to a window all day — like I do in my home office — you are getting UVA exposure on one side of your face for hours. Truck drivers in studies show significantly more sun damage on the left side of their face (the window side).

When You Actually Need It Indoors

• Yes: You sit directly next to a window for more than an hour a day
• Yes: You have a long commute where sun hits one side of your face
• Yes: You use products with retinol, AHAs, or other photosensitizing ingredients — your skin is more vulnerable
• No: You work in a windowless office or far from windows
• No: You have UV-blocking film on your windows

What to Use

A lightweight SPF 30 moisturizer is enough for indoor use. You do not need the heavy beach sunscreen. Mineral sunscreens with zinc oxide or titanium dioxide are better for daily indoor wear because they do not degrade as quickly and are less likely to irritate your eyes.