TL;DR: The 'no sunscreen indoors' line predates modern indoor life. UVA passes through windows, screens emit visible light, and most of us aren't really indoors anyway.
Quick answer
Indoor environments have real UV exposure. UVA passes through window glass. Computer screens emit modest visible light. And most “indoor only” days include unintended sun exposure — the walk to lunch, errands, ten minutes on the balcony. Daily SPF still matters for indoor workers. The advice that you don’t need sunscreen indoors was based on older indoor environments without significant glass or screens. The modern reality is that most indoor workers have meaningful, mostly-UVA exposure throughout the day, and UVA is the wavelength most responsible for the visible signs of aging.
The basic UV facts
UVA is long-wavelength UV. It causes most of what people call premature aging. It passes through window glass at 60–80% of intensity, through clouds substantially, through most car windshields better than nothing but not completely.
UVB is short-wavelength UV, the primary burning radiation. Mostly blocked by glass.
Visible light, especially the high-energy blue end, is an emerging concern for melasma and other pigmentation, and matters more for some skin types than others.
UV plus visible light combined is an ongoing aging factor even when you’re not in direct sun.
What “indoor” actually means
True indoor with no windows and no screens means minimal UV exposure. SPF is less critical here, though it still adds modest defense.
Office indoor with windows means meaningful UVA exposure during work hours. Home with windows is the same. The fact that you can’t see UV doesn’t mean it isn’t there.
Driving counts as outdoor exposure on one side of your face, because UVA penetrates car windshields significantly. Truck-driver photography studies showed dramatic aging asymmetry on the window side. Real-world evidence of cumulative UVA at work.
In front of a computer, you’re getting modest UV and visible light contribution from the screen. Lunch breaks, walks to the bathroom, errands — brief but cumulative.
For most modern people, “indoor” still includes meaningful UV exposure.
What the studies say
Multiple studies confirm 60–80% of UVA passes through standard window glass. Studies comparing indoor and outdoor workers show meaningful but smaller differences in age-related skin changes, which lines up with the idea that indoor exposure is reduced but not zero. Newer research on visible light contributions, especially in pigmentation-prone skin, has been building over the past decade.
The driver-side aging asymmetry studies are the cleanest evidence. Same person, same age, dramatic difference between the side of the face getting UVA through the window and the side that isn’t.
When to wear SPF
Daily, regardless of indoor or outdoor. All year. The “every day” habit beats “only on sunny days” or “only when I’m going out” because most days you don’t actually know in advance what your exposure will look like.
For everyday indoor wear, SPF 30+ broad-spectrum is sufficient. The discipline isn’t about choosing a higher number for indoors — it’s about applying the right amount consistently.
Specific concerns by skin type
For melasma-prone skin, visible light blocking matters. Tinted SPF with iron oxides is the only thing that meaningfully blocks visible light, so it’s essentially required. Indoor SPF is strict.
For pigmented skin, the PIH risk is higher, and daily SPF prevents pigmentation accumulation that becomes harder to fade later.
For mature skin, cumulative UVA effects are more visible. Daily SPF continues to matter and arguably matters more.
For sensitive skin, mineral SPF is often preferred. Daily indoor protection is still relevant.
For acne-prone skin with PIH, SPF keeps the marks left behind from breakouts from darkening further.
What about screens
Computer screens emit modest high-energy visible light, limited UVA, and the contribution to skin aging is cumulative but small. Smartphone screens are similar.
Visible light matters more for pigmentation-prone skin than for general aging. Tinted SPF helps. The “blue light skincare” trend is partly real and largely overhyped — daily SPF captures most of the protective benefit anyway.
Common mistakes
Skipping SPF on cloudy days. UVA penetrates clouds.
Skipping SPF on indoor days. Window UV is real.
Believing windows block all UV. They block UVB. They don’t block UVA.
Wearing SPF only in summer. Year-round application matters; UVA isn’t seasonal.
Reapplying only when in direct sun. Indoor reapplication usually isn’t needed; morning application is non-negotiable.
A practical protocol for indoor workers
Morning: apply broad-spectrum SPF 30+ generously (the quarter-teaspoon amount for the face). Wait a minute or two for absorption. Layer makeup over the top.
During the workday, the morning application generally lasts. If you’re near windows for hours, reapply at lunch. Stick or powder SPF makes makeup-friendly touch-ups easy.
For outdoor breaks, reapply if you’re outside for two hours or more. Hat and sunglasses help.
For the car commute, apply hand SPF before driving. Reapply face SPF at your destination if morning was many hours ago.
Reapplication, realistically
For indoor days, single morning application typically suffices.
For days with significant outdoor exposure, reapply every two hours.
The midday touch-up earns its place when it covers errands or lunch outside, refreshes protection, and ensures you don’t forget when you do step out.
A few common myths
“Window glass blocks UV completely.” It doesn’t. Only UVB.
“Screens emit dangerous UV.” Limited UV; some visible light contribution.
“Indoor lighting causes skin damage.” LED and fluorescent lights produce minimal UV. Not a meaningful aging factor.
“You can’t burn indoors, so SPF isn’t necessary.” Burning is UVB. The aging from indoor exposure is mostly UVA, which doesn’t burn but does age.
“SPF in foundation is enough indoors.” Almost never. You’d need to apply far more foundation than anyone does to hit the labeled SPF.
Daily SPF as a habit
The discipline of daily SPF makes the indoor-vs-outdoor question moot. It captures the cumulative exposure benefit. It’s probably the single most impactful skincare habit at the population level. And it’s freeing — you stop adjudicating each day’s exposure level and just apply.
Most people benefit from automatic morning application as habit, like brushing teeth. Not because every day is a beach day, but because the decision is made.
Where the evidence is strong, where it isn’t
Strong: UVA passes through windows. Daily SPF reduces visible aging substantially over decades. Indoor workers benefit from daily SPF.
Moderate: Visible light contributes to aging. Computer screens contribute modestly. Tinted SPF outperforms non-tinted in pigmentation scenarios.
Weak: “Blue light blocker” creams as a significant addition beyond a normal SPF. Specific “screen-time SPF” formulations. Brand-specific anti-screen claims.
The straightforward daily SPF habit captures most of the benefit. The marketing layered on top is mostly marketing.
FAQ
If I only get brief outdoor sun, do I need SPF on cloudy days? Yes. UVA still passes through.
Does my morning SPF last through the workday? Roughly, if you’re not in direct sun. Reapplication makes sense for extended outdoor exposure.
Realistic UV exposure of a typical office worker? Modest but real, mostly through windows. Daily SPF captures the benefit over time.
Should I wear SPF when sleeping? No. UV at home with no windows during sleep is essentially zero. Skip overnight.
Will my skin be measurably better at 50 if I wore daily SPF as an office worker? Yes. Substantially.
Sources
Krutmann J et al. The skin aging exposome. Journal of Dermatological Science, 2017. AAD position on daily SPF use, 2024.
Keep reading
Keep reading
- Sleep, Stress & WellnessBlue light and skin: real risk, smaller than the marketing
- The Elelaf EditSkin purging is real, but often misdiagnosed
- The Elelaf Edit‘SPF in makeup is enough’: why it almost never is