Most online theories about how fragrance oil works in candles are nonsense.

They’re usually based on someone’s limited experience, a viral post, or a horror story, but the science is clear: candles burn safer with a more consistent hot throw when fragrance oil is added at the right temperature during its creation.

Add fragrance oil to wax when the wax temperature is between 185°F and 200°F (85°C – 93°C) for a safer, more stable candle design.  Fragrance oil does not degrade unless it reaches its boiling point, which is far above 200°F, and should not be a concern for candle makers.  This idea applies to any wax for any type of candle.

In this post, we’ll discuss the science behind fragrance oil and candle performance by highlighting a few basic ideas.

Flash point doesn’t matter

Most bottles of fragrance oil list the flash point somewhere on the packaging.  

As we’ve discussed, this temperature is an important indicator for suppliers shipping oils worldwide.  For safety reasons, oils with flash points below a certain legal threshold cannot be flown and must be shipped on the ground.

Legal needs aside, the flash point often becomes a divisive issue in candle-making communities.  Some suggest this temperature should be when you add it to the melted wax.

Others believe your hot throw will be ruined if you heat the fragrance oil above that temperature.

Both of these assumptions are false and potentially dangerous.

It is scientifically unlikely that fragrance oil will degrade within normal candle-making process temperatures because it is significantly lower than the oil’s boiling point.  When fragrance oil is added at too low of a temperature – such as some fragrance oil’s flash points – the risk of a candle over-igniting increases.

The oil doesn’t mix as well and risks creating flammable “pools” inside the candle waiting to be ignited.

Adding fragrance around 185°F allows fragrance oil to blend more appropriately throughout the candle for a safer, more consistent burn.

Lids don’t protect cold or hot throw

Some people declare that candles should be cured and stored with their lids or they’ll risk losing their throw.

This isn’t true because scent is stored in the fragrance oil mixed throughout the candle.  While there may certainly be some evaporation from the surface of the solid candle, it’s unlikely to matter once the candle is burned and releases additional fragrance.

Lids are great for protecting candles from gathering dust but aren’t required to sustain cold or hot throw.  If your candle doesn’t throw well, it’s most likely due to wick selection and how well a fragrance oil operates in your wax.

Fragrance oil temperature mostly impacts safety

Fragrance oil added at the proper temperature range – 185°F to 200°F (85°C – 93°C) – blends safely with wax and creates consistent candles.

In general, fragrance oil mixes in with hot wax, eventually getting trapped throughout the wax as it cools.  When a candle is burned, the solid-turned-liquid wax melt pool contributes to the overall scent throw of the candle.

There are many ways to improve hot throw, but adjusting the temperature you add fragrance oil isn’t one of them.

Not safely, at least.

Fragrance oil added below the accepted range risks creating pockets of FO that aren’t neatly blended throughout the candle because the wax was never heated to a temperature that allowed all the additives and crystal structures to break fully down into a liquid that can hug the fragrance molecules while cooling.

Those pockets will stay trapped in the candle.  While the candle burns, if the open flame encounters a pocket of fragrance oil, there is a real risk of violent ignition.  The other way this mistake manifests is a “wet” candle bottom: the fragrance pools at the bottom of the vessel, which kills your hot throw.

The only exception is to ensure the entire blend is heated all the way up.  At that point you might as well wait to add fragrance until the wax is hot enough.