Can you tan through a window?

“It is unlikely to get tan through a window but it depends on various factors such as type of glass window, the strength of the sunlight, and how long you are exposed to sun rays.”

A lot of times we go to the beaches to take sunbath. Some people go to boast their immunity by getting vitamin D and some just go to get tanned. But have you wondered do you really need to go to the beach (outdoor) or you can get tanned by just sitting under sunlight coming through the window?

If you are looking for vitamin D, then the answer is no. You can’t have vitamin D by just sitting under the sunlight from the window glass. And if you are looking for skin tanning, then the answer is maybe or may not be. Let’s first understand what is tanning and what causes tanning

What is tanning?

Tanning is a process in which skin gets darkened due to exposure to sunlight. The tanning effect can be produced without exposure to sunlight using artificial sources such as tanning lamps or tanning sprays. This process is called sunless tanning.

What causes tanning?

Tanning process occurs in the skin when the natural pigment called melanin is produced by melanocytes cells when they react with ultraviolet rays from sunlight. There are two types of melanin produced pheomelanin (red) and eumelanin (very dark brown). This melanin protects our body by absorbing UV rays. When we are excessively exposed to UV rays, the body releases more melanin in order to combat, and hence, the skin color gets darken.

There are mainly two UV frequencies responsible for skin tanning: UVA and UVB

Skin tanning due to UVA

UVA is ultraviolet radiation whose wavelength ranges from 320 to 400 nm. These UVA rays oxidize the pre-existing melanin from melanocytes in the skin which turns the skin color to brown. UVA is known to penetrate deeper layers of the skin and responsible for causing wrinkling, skin aging, and inducing indirect DNA damage which may cause some skin cancer.

Skin tanning due to UVB

UVB has a wavelength range of 280 to 320 nm which mostly penetrates the topmost layer of the skin. Most of these rays are blocked by the ozone layer. This UVB is also responsible for producing vitamin D in human skin. Overexposure to these rays might cause sunburn, direct damage to DNA, skin aging, and most of the skin cancers.  

Do You Know?

UV-C is the most damaging type of UV radiation and does not reach the earth’s surface because it gets completely filtered by the atmosphere

Now we know what causes tanning. Let’s try to understand what happens or what factors are involved when we sit under the sunlight coming through the glass window.

In outdoor conditions, we are directly exposed to the UV rays but when we are inside the house, UV rays come in our contact indirectly. Sunlight has to pass through window glass and can enter only when it is at some angle.

How tanning gets affected by the type of windows glass?

The amount of UV radiation (UVA and UVB) allowed by a fabric or material to reach our skin is indicated by the Ultraviolet Protection Factor (UPF). For example, House windows have UPF of 10 which means one-tenth of the UV rays will pass through it, and the remaining 90% will be absorbed or blocked.

UPF RatingProtection Category% UV radiation Blocked
UPF 15 – 24Good93.3 – 95.9
UPF 25 – 39Very Good96.0 – 97.4
UPF 40 – 50+Excellent97.5 – 98+

Office building glasses have 50+ UPF which means they can block more than 98% of UV rays. Front windshield of a car have UPF of 50+ while the side windows have 12 UPF which means if you have more chances to get tanned if you are exposed to sunlight from side windows as compared to front windshield.

The UPF value of the window glass in your house will determine your exposure to UV rays. Almost 90% of the UV rays are blocked by home window glass, therefore there is less chance to get tanned. Double glazed window glasses will lower the UV exposure further as compared to normal glass.

Do You Know?

Only 10% of UV-B radiation does reach the earth’s surface

Levels of ultra violet rays

The exposure to UV rays also depends on the level of the UV radiation present in the environment. The UV index is a scale used to indicate the risk of sunburn due to UV radiation. The high value of the UV index represents a high level of UV rays.

UV Index has five categories:

CategoryUV Index
Low1-2
Moderate3-5
High6-7
Very High8-10
Extreme11+

The factors that affect the level of UV rays are

Sun Elevation: The level of UVR is high during the middle of the day and summer. In the middle of the day, the sunrays are almost perpendicular to the earth’s surface. Therefore they can’t enter the house through the side windows. Sunlight can enter through the glass window only during sunrise and sunset when the rays are at some angle. But the level of UVR in these rays is less as compared to rays during the middle of the day.

Do You Know?

60% of UV radiation is received between 10 am and 2 pm daily

Latitude: People living closer to equatorial regions are exposed to more UV radiations.

Cloud cover: Heavy cloud cover can reduce the level the UV rays.

Altitude: The atmosphere is generally thinner at higher altitudes which allows more UV rays to pass. Therefore people living at higher altitudes are exposed to higher levels of UV radiation.

Do You Know?

UV Radiations increases by 4% for each 300-meter increase in altitude

Reflective surfaces: The reflective property of the ground near the windows also affects the level of UV rays passing through the window glass. The presence of shade can reduce UV Radiation by 50% or more. Sand reflects up to 25% of UV radiation.

Do You Know?

Clean snow reflects up to 80% of sunburning UV Radiations

Exposure time

The more time you are exposed to UV radiations, the more dark-brown melanin pigments will be produced which will tan our skin color.

Should you use sunscreen inside the house?

Yes, if you have exposure to high levels of UV rays. Glass windows are less efficient to block UV-A rays which penetrate our skin deeper and cause damage such as sunburn, wrinkles, and cancer. Therefore it is better to take precautions to avoid sunburn and other skin damage.

Do You Know?

Indoor workers receive 10-20% of outdoor workers yearly UV exposure

As we know now there are many factors such as the level of UV rays, time of the day, location of the house, altitude, and UPF of glass is involved in the tanning of skin through the window. Therefore it is very less likely to get tanned through the glass window.

Here is an interesting fact for you.

Do You Know?

It is a common misconception that you can ‘feel yourself getting sunburnt’. Solar UV Radiations cannot be seen or felt so it can damage our skin without us knowing.

Professor Atom

View posts by Professor Atom
Professor Atom is a science enthusiast and alumni of IIT Bombay. According to him, every question can be solved with curiosity and mind mapping. ( Curiosity = Asking Questions = Learning )

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