Does sunscreen block vitamin D?

Bottom lineSunscreen filters most UV-B, so in theory it nearly stops vitamin D production - but real-world studies show typical sunscreen users are not meaningfully more deficient, because nobody applies it perfectly. Keep wearing it at high UV; if you want vitamin D from sun, take a short unprotected window well below burn threshold first, or cover the gap with food and supplements.

In theory, almost completely. In practice, not nearly as much as you would expect - and you should keep wearing it.

The theory vs the reality

Vitamin D is made when UV-B rays hit bare skin, and UV-B is exactly what sunscreen filters: SPF 30 blocks around 97% of it when applied the way the label assumes. In laboratory conditions, that shuts vitamin D production nearly down.

Real-world studies tell a friendlier story. People who use sunscreen regularly are generally not more vitamin D deficient than people who do not - because almost nobody applies the full recommended amount, evenly, to every exposed area, and reapplies on schedule. Enough UV-B slips through typical use to keep some synthesis going.

What this means for you

• Do not skip sunscreen to boost vitamin D when the UV index is high. The extra vitamin D is modest; the extra skin damage is not.
• If you want a deliberate vitamin D window, take a short unprotected stretch well below your burn threshold at moderate UV, then apply sunscreen for the rest of your time outside. How much sun that takes depends on your skin tone and the UV index.
• If you are diligent with SPF year-round (good for your skin), consider covering vitamin D with food or a supplement instead - the daily guideline is 600 IU (15 mcg), and the vitamin D converter translates label units.

Femora's Sunshine feature accounts for this directly: when you start a sun session, you tell it whether you are wearing SPF 15 through 100, and the vitamin D estimate adjusts.

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