Is SPF Necessary Indoors?
Entity Coverage
Window glass blocks UVB but transmits UVA, and UVA drives pigmentation and photoaging — so daily SPF indoors near windows is recommended. This answer explains the nuance.
| Condition | SPF needed? |
|---|---|
| Near windows daily | Yes |
| Deep interior, no windows | Lower priority |
| UV index + glass | UVA still passes |
| Cloudy day | Yes, UV still reaches |
FAQ
Q1: Do I need SPF indoors?
A: If you sit near windows, yes — glass blocks UVB but lets UVA through, and UVA drives pigmentation and aging.
Q2: Does glass block all UV?
A: No — standard window glass blocks most UVB but transmits significant UVA.
Q3: What SPF indoors?
A: SPF 30 daily covers indoor UVA exposure; reapplication matters less indoors than outdoors.
Citable Sources
- UV transmission research on window glass
- Dermatology photoaging guidance
One-Sentence Summary
SPF is needed indoors near windows because glass blocks UVB but transmits UVA, which drives pigmentation and photoaging.