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Why Does Sunlight Remove Stains?

Before the 20th century, history shows us sunlight was used to not only dry laundry but also for bleaching whites and brightening practices in general. Today we’ve resorted to harsh chemicals and abrasive techniques to remove stains, but is that necessary? How does sunlight work to remove stains?

Sunlight removes stains and brightens whites by breaking down the bonds in the stains to the point where they can no longer hold. The ultraviolet radiation in sunlight does this by breaking down molecules and their bonds via chemical reactions

This article will discuss the science behind sunlight, explaining why it can remove stains, as well as its effects on color. There are even some useful tips for household chores, and by the end, you may come to find that when life gives you lemons, you should do the laundry.

Why does sunlight remove stains

Our Favorite Star: The Sun

Warm, bright, and beautiful, our sun is the big light in the sky that dictates the fate of everything on the planet. Scientists have discovered that it is composed of 90% hydrogen, 9% helium, and trace amounts of about 65 other chemical elements. The interaction between these elements creates the radiation of energy that we call sunlight.

Sunlight is emitted via rays that are a form of electromagnetic radiation, and only a small portion of the electromagnetic spectrum is even visible to the naked eye. And it’s somewhere within that electromagnetic spectrum that we find UV or ultraviolet light, which is why sunlight removes stains, among many other things. So let’s look at a few facts science has to offer about it.

UltraViolet (UV) Radiation

Sunlight is only 10% UV radiation, and only about one-third of that breaks through the atmosphere to reach the ground. Yet the power of UV light is so strong that we still see and experience the effects on Earth even with a comparatively small amount. How strong is it? For one thing, UV radiation produces enough energy to break molecular bonds and other essential connections that are the reason things are what they are.

When this happens, certain chemical reactions may occur, which affects physical properties (like color or size), and often things will change into something new altogether. In the case of living tissues or organisms, these kinds of reactions can cause serious damage, if not total disintegration or death. Sometimes we find this to be hazardous, but other times it’s beneficial. 


For example, while some UV rays help your body produce vitamin D and absorb other minerals, the more harmful ones will cause damage to the skin. A suntan is a reaction to the damage those rays create. When the body senses this damage occurring, skin cells called melanocytes will produce a pigment called melanin. This darkens the skin and works to absorb UV light in an attempt to protect the skin from sustaining any further damage. 

Once you have a suntan, however, and continue to be exposed to the sun, UV radiation inevitably overwhelms your body’s defenses, and a toxic chemical reaction occurs that results in sunburn. Essentially, you start to break down on a molecular level that isn’t healthy. And it’s those types of reactions that, if extended over time, may lead to bigger problems, like skin cancer, for instance. 

UV: The Un-Vaccine

The positive side of these more powerful UV rays is that they can destroy a multitude of harmful living organisms, including viruses and bacteria. Despite what recent search results may offer you these days, science has shown that sunlight is extremely effective in destroying these diseased creatures of microscopic proportions. It’s all in the chemical reactions. 

Countless studies prove this amazing efficacy of UV light as a sanitizer and disinfectant capable of neutralizing most viruses and bacteria no matter where they try to hide. It has been shown to work in the air, food and drinks, sanitizing water, and over a vast range in temperatures

And all of that science agrees: it’s a sure thing. You can find items like the UV Light Sanitizer Wand on Amazon for safe use at home to help keep the family healthy, and rest easy knowing that even the nastiest, most political of viruses cannot survive this natural phenomenon.

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Why Sunlight Removes Stains

So if you think about it, stains are merely an undesired molecular bond via a chemical reaction with the item these molecules are staining. A second chemical reaction will occur when you put the stained item in the sun that can counteract this. 

The UV rays will work on the stains by breaking up their bonds, essentially detaching the stain matter from stained matter altogether, as if it were never there in the first place. Sunlight can clean several items around the house in this way.

Nature’s Bleach

Over time, sunlight may cause colors to fade, perhaps even turn them completely white. (Maybe you have a chair on the patio that can attest to this.) The science behind this works on the same wavelength we’ve been on with stains. Only it does require we examine other wavelengths… 

This 2-minute video gives a basic overview of the electromagnetic spectrum and shows the various wavelengths of visible light (the rainbow portion of the spectrum). It will help you to further visualize everything being discussed here:

Colored things only have color because they absorb certain wavelengths of visible light—specifically, they absorb some wavelengths and reflect others. The wavelengths they reflect, or “cast off,” will be the color we see. 

It is important to remember that color is a physical property that can be altered by a chemical reaction. In particular, an object’s ability to absorb certain wavelengths of light will be affected, and we observe a difference in color. Prolonged exposure to UV sunlight in an object with color can harm the object’s ability to absorb or deflect the light wavelengths that it normally would, causing the object to appear faded over time.

And while this effect may not be so great for lawn furniture or other colored objects, it is great for white items, most notably clothes and other linens. 

The Bleaching Grounds of History

It was commonplace for centuries for people to lay out their laundry in the sun. Large plots of land were specially chosen and designated for this chore. Not only was this the method used for drying, but techniques for bleaching and brightening whites were utilized as well. There was even a laundry detergent in the 1800s called Sun Soap, named with this very practice in mind. 

This method in laundry service eventually fell by the wayside, as modern advancements made it so we could wash and dry indoors with automated machines and chemical concoctions. But with so much historical evidence and scientific support showing sun bleaching is effective, it makes one think about taking a step back when it comes to this task. Perhaps, take a step back outside and into the sunlight.

Lemon’s Aid in the Fight Against Stains

Lemon juice is a powerful citric acid that will either cause a chemical reaction or act as a catalyst for one, which means that when it is applied to a dirty or tarnished item, it will either remove the stain or break it up so that it can be removed by wiping away or laundering, for example.

Lemons are great for removing many stains—including rust!—and tackling several other jobs around the house. And when doing the laundry, adding some lemon juice with your detergent may be all the stain-fighting power you need. Washing items with lemon and then laying them out in the sun to dry is then the winning combination for bright, clean, fresh items that look, feel, and smell amazing.

Why does sunlight remove stains

Outdoor Laundry at Home

Clotheslines were a chosen alternative to laying laundry on the ground for a variety of reasons. For one, it kept wild pigs and other creatures from soiling or even eating one’s laundry. And while that may not be a big concern today, at the very least, a clothesline will save you space when you use this technique at home. 

Drying and bleaching are most effective when an object has maximum surface area exposure, so it’s suggested you use clothespins to clip items to the clothesline rather than just draping items over it. These Honey-Can-Do Plastic Clothespins from Amazon are a great option because they are sturdy and hold a lot of weight. Here are some more tips to get you started.

Honey-Can-Do Colored Plastic Clothespins, 100-Pack


Sunlight is capable of removing stains as the ultraviolet radiation in sunlight can break down the stain at the molecular level to destroy it. This is an effective technique in bleaching whites and brightening laundry that has been used throughout history. Lemon juice is also a great stain-fighter that can be used in conjunction with sunlight to make for a fresh, clean, and healthy home.


  • Jake Alexander

    Jake is a freelance writer from Pennsylvania who enjoys writing about science and sports. When he's not writing for Temperature Master, he can be found watching the NFL or playing basketball with his friends.

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