Sunday, September 24, 2023

Why Skin Cannot Make Vitamin D from Sunlight Through Windows

Sunlight coming through glass windows cannot make vitamin D in the skin but it can still cause its premature ageing.

Our skin makes vitamin D on exposed to sunlight. However, our indoor lifestyle prevents adequate sun exposure.

In many countries, during winter, the sun rises after one is inside the office, only to set before office time is over. The weather outside may also need one to bundle up, allowing no scope of getting sunlight on the skin. On the other hand, summers are hot and humid in some countries, making people reluctant to be outdoors.

So you may think: Why not work inside an office cabin that has large window panes? The room will have a controlled temperature and the sunlight percolating through the windows can make vitamin D in your skin. Here is the science behind why it will not work or rather, will be fairly dangerous.

Sunlight, Skin, and Vitamin D

When sunlight falls on the skin, certain chemicals in it make raw material for vitamin D. This process needs a part of sunlight needed for this is called ultraviolet-B or UV-B rays.

Glass and UV-B Rays

The window glass does not absorb most of the sunlight, including the visible light. That is why you ‘see’ the window to be transparent. However, glass absorbs most of the UV-B rays.

As a result, the sunlight that comes through the window pane has most of its rays except UV-B ones. Such light will not produce any vitamin D in the skin even after hours of exposure.

Dangers of Sunlight Through Windows

There are some other rays in the sunlight called UV-A rays. They are also invisible to the eyes, being ultraviolet ones. However, they are absorbed very little by the glass. So more than fifty per cent of the UV-A rays in the sunlight penetrate the window glass and fall on the skin.

UV-A Rays and Skin Damage

  • Prolonged exposure to UV-A rays is known to cause premature ageing of the skin, making it saggy, wrinkled, thick, and leathery.
  • UV-A rays also increase the risk of dangerous skin cancers called melanomas.
  • A study showed that black skin allowed only 7.4% of UV-B rays and 17.5% of UV-A rays to penetrate further, while white skin allowed 24% of UV-B rays and 55% of UV-A rays inside. In other words, dark skin is nearly twice as protective as fairer skin, though many sun exposure studies show much higher UV-ray absorption in darker skin. Take this number as the baseline—the minimum additional benefit of dark skin.


By sitting behind the glass windows in an office cabin:

  • You don’t get any UV-B rays to make vitamin D.
  • You keep getting continuous exposure to harmful UV-A rays, with the exposed skin potentially ageing prematurely.
  • The UV-A rays reach you even if you are within a few feet of the office windows.
  • If you have to sit next to a window for long hours, apply sunscreen with good UV-A protection every few hours.
  • Darker skin gives more protection from UV-A. So fairer skin people should use stronger UV-A sunscreen than their brown and dark-skinned colleagues.

To Read More

First published on: 8th December 2021
Image credit: Mikhail Nilov on Pexels
Last Updated on: 26th June 2023


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.



Latest Articles