Do UV Sun Rays Go Through Windows?

The answer is yes! Usually, some important UV sun rays do come through window glass.

UV Sun Rays and Your Window

Recently, a reader sent me this question as a comment to one of my blog posts. It's such a great question, and patients often ask me this so I decided to answer it here.

You may think that you don't need to worry about sun damage when you're indoors, but that's not true if you're sitting in front of a window.....

Here is the question that blog reader John asked:

Hi Dr. Bailey,

I work in a “trendy” office with floor to ceiling windows on all the outside walls. I know many commercial buildings now have UV window film that appears untinted to the human eye but block almost all UV radiation. Is there any way to tell if the window next to me has this type of filtering in place? It would save me from reapplying sunscreen at my desk every 3-4 hours!

Best Regards and love the blog! John

Hello John,

This is a really important issue for anyone sitting in direct sunlight that comes through a window.

Normal glass blocks all of UVB but allows UVA to come through.

Both of these rays are harmful to skin.  Remember:

UVB skin damage

• UVB is considered the main sunburn ray.
• UVB rays are shorter and mostly damage the top layer of your skin causing thinning and skin pigment problems such as sun spots and melasma.
• It causes skin cancer and sun damage.
• The SPF in a sunscreen tells you how well the product protects you from UVB.

UVA skin damage

• Is the UV ray in tanning beds.
• UVA rays are longer than UVB and penetrate the skin more deeply to play a big role in sun damage including wrinkles. They also worsen stubborn skin pigment problems such as melasma and sun spots.
• It can cause skin cancer.
• The SPF on sunscreens tells you only a little about whether the product protects you from UVA. Look for sunscreens labeled "broad spectrum," but even then, full UVA-protection is more complex.

Bottom line for sunscreen to protect your skin from UV rays through windows

I recommend mineral zinc oxide sunscreens for the best, most reliable UVA protection (click here to read more).

How do you know how well your window blocks UV rays?

As you point out, some modern windows block most all of the UV sun rays including UVA.

Finding out which windows were used in the construction of your building might help you know how well they block UVA. It's possible to block up to 99.9% of UV waves with today's modern technology.

The Skin Cancer Foundation has information on window UV film, click here to see it. In general, you can add sheets of UV-blocking film to windows, or purchase glass that includes technology to block UV rays.

In the past, the Skin Cancer Foundation provided a list of window films that they had investigated for reliability. They have stopped doing that. Now, you have to do the research on your own.  The best way to accurately test how much UV passes through your windows would be to finding someone with a radiometer that measures the UV transmittance. I know that is not practical!

How to sun protect your skin if you sit in front of a window

For my patients who sit in a place where direct sunlight comes in through window glass, I recommend:

1. Wearing a mineral sunscreen on all exposed skin, and
2. Wearing clothing that blocks UV rays. Click here to read about sun protective clothing. Thick fabric is often adequate for sun protection. UPF 50 fabric has been designed and tested for UV protection. My favorite UPF 50 fabric is that made by Coolibar because the fiber technology is unique and very reliable. 

Tinted windows don't block all UV rays

If you have windows that claim to block UV rays, it is important to point out that a very tiny amount of UV still gets through. As I mentioned above, it's possible to block 99.9% of UV rays, but even if their windows are that good, the 0.1% can add up at 8 hours a day, 5 days a week. Wrinkles, age spots and skin cancer just ain't worth it!

For exposure through windows that don’t claim to block UV rays, I definitely tell my patients to reapply mineral sunscreen every two hours if they can't move out of the direct sunlight. It's also time to get creative about trying to create shade, too. That would be pretty tough in a "trendy" office building with floor-to-ceiling windows, which is what makes this question such a challenge.

My favorite easy-to-wear broad spectrum zinc oxide sunscreens include my Sheer Strength Pure Physical Mineral Sunscreens. They are formulated with the highest standards and best invisible zinc oxide non-nano UV sunscreen. They are lightweight, never feel greasy, rub in invisibly, are fragrance free and ideal for even the most sensitive skin. I have a tinted product that even blocks visible light capable of contributing to stubborn skin pigment problems. Click here to see my Sheer Strength Sunscreen line and find a product that's right for your needs. 

I personally wear my Matte Tinted SPF 30+ Sunscreen on my face and the Sheer Strength Invisible or Water Resistant Spray SPF 50+ on my neck, ears, chest, back of my hands and any other exposed skin daily. I dust the SPF Refresh Powder Sunscreen on during the day when I am outdoors. I give these products as gifts because they are truly unique and everyone that uses them loves them.  

For more information on these and all of my sun protection products and kits, click here.

You’ve asked an excellent and important question. Best of luck.

Warm Regards,

Cynthia Bailey MD, Dermatologist

If you have questions about skin care or skin health, please send them to me using the Contact Dr. Bailey button at the top of the page.

Disclaimer: Please realize that availing yourself of the opportunity to submit and receive answers to your questions from Dr. Bailey does not confer a doctor/patient relationship with Dr. Bailey. The information provided by Dr. Bailey is general health information inspired by your question. It should not be a substitute for obtaining medical advice from your physician and is not intended to diagnose or treat any specific medical problem (and is not an extension of the care Dr. Bailey has provided in her office for existing patients of her practice). Never ignore your own doctor’s advice because of something you read here; this information is for general informational purpose only.