You’ve bought a beautiful, crisp white candle to match your decor.
It sits proudly on your coffee table for a few weeks, smelling divine and looking splendid.
But then, one day, you notice something strange. It isn't bright white anymore; the surface has developed a slightly murky, yellowish tinge.
It’s incredibly frustrating, isn't it?
If you have found yourself asking, "Why do candles turn yellow?" rest assured that you are not alone.
This common issue isn't usually a sign of a faulty product or poor craftsmanship.
Instead, it's often a fascinating, a bit annoying, lesson in chemistry and physics happening right in your living room.
It is essentially a process of decay caused by the environment around the candle.
Let’s explore the science behind this transformation and, crucially, how you can stop it from happening.
The main culprit: Ultraviolet (UV) light
When looking into candle wax discolouration, the biggest offender by far is light. Specifically, ultraviolet (UV) light.
You might think your candles are safe indoors, but UV rays are powerful and sneaky.
They are present in sunlight and can easily penetrate glass windows.
If your candle is sitting on a windowsill or on a table that gets a few hours of afternoon sun, it is being bombarded by UV lights.
The science of photo-oxidation
So, what is happening on a molecular level? It comes down to a process called photo-oxidation.
Whether your candle is made from natural wax, beeswax, or paraffin, it is composed of complex chemical bonds.
When UV light hits the candle, it provides energy that can break these bonds. When the bonds break, the molecules react with oxygen in the air.
This reaction changes the chemical structure of the wax on the surface.
This new structure reflects light differently, causing the human eye to perceive a yellow, or sometimes even brownish, tint instead of white.
Think of it like an old newspaper left in the sun, it yellows and becomes brittle over time. Your candle is doing the exact same thing.
It isn't just direct, blazing sun that causes damage. Even indirect, ambient daylight over many months can eventually cause sun damage to candles.
It’s not just the wax: The role of fragrance
While the wax itself is susceptible to UV rays, the fragrance oils added to create those lovely scents often accelerate the yellowing process significantly.
Some fragrance compounds are much less stable than others.
When these specific ingredients are exposed to light (and air), they oxidise very quickly, turning the surrounding wax yellow almost like a dye.
The "Vanilla" problem
If you are a fan of gourmand scents, you have likely noticed this problem more often.
Scents containing vanillin (the primary component of vanilla bean extract) are notorious for turning yellow or even brown very quickly.
Vanillin is highly reactive to both light and oxygen.
Even high-quality candle makers struggle to keep a strong vanilla scent perfectly white for long periods.
Other fragrance notes that are prone to rapid discolouration include:
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Heavy citrus scents (like orange or lemon)
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Some floral notes like jasmine
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Certain musks and spice blends
If you have two candles side-by-side on a windowsill, one unscented and one heavily scented with vanilla, the vanilla one will almost certainly turn yellow much faster.
Is a yellow candle safe to burn?
The short answer is yes, absolutely.
While the discolouration might be aesthetically annoying, especially if it ruins the look of your room decor, it is generally just a cosmetic issue.
The chemical changes are happening on the very surface layer of the wax.
When you light the candle, it should burn just fine.
In fact, once the top layer of wax has melted into a liquid pool, the yellow tint often disappears into the clear liquid, and the fresh wax underneath will likely be white.
The scent throw should not be significantly affected either.
How to prevent candles from yellowing
Now that we understand the science behind why candles turn yellow, we can take steps to prevent it.
Protecting your collection is all about controlling the environment.
Here are the best ways to keep your wax looking pristine:
1. Location, location, location
The most critical step is to keep your candles out of direct sunlight.
Avoid windowsills, conservatories, or shelves that get hit by sunbeams during the day.
A darker corner of the room or a bookshelf away from the window is ideal.
2. Utilise lids
If your candle came with a lid, use it!
When you aren't burning the candle, pop the lid back on.
This is a simple but highly effective barrier that blocks out UV light and also limits the wax's exposure to oxygen and dust.
3. Proper storage
If you have a collection of seasonal candles that you won't be using for a few months, don't leave them out on display.
Store them in a cool, dark cupboard or a drawer.
Darkness is a candle's best friend when it comes to longevity.
4. Choose coloured glass
Candles that come in amber, dark green, or opaque frosted glass jars are naturally better protected than those in clear glass.
The coloured glass acts like sunglasses for your candle, filtering out a significant portion of harmful UV rays.
Suggestion: Read our post on does candle wax expire?
It can be frustrating to see your expensive collection lose its sparkle, but understanding why candles turn yellow is the first step to preserving them.
Remember, it is usually just cosmetic damage caused by the relentless energy of UV rays or highly reactive fragrances like vanilla.
The good news is that a yellowed candle is almost always perfectly safe to enjoy.
Just move them out of the sun, pop a lid on when they are cool, and enjoy the fragrance!
Have you had a candle turn a surprising colour? Let us know your experience in the comments below!
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