We know that essential oils are flammable, some having quite a low flashpoint.. The flashpoint of certain oils is low enough, and the heat of the dryer is high enough. Finally, though there is a theoretical risk, many people successfully use essential oils in the dryer, usually on dryer sheets or wool balls.
Naturally Fragrance Your Clothing, Sheets and Towels AFTER Washing and Drying by Using Aromatic Sachets. Since essential oils are flammable and should not be used in the dryer (and can potentially still pose a fire hazard when used in the wash cycle), a safer alternative is to use an aromatic sachet.
Aromatherapy, Dryer Sheets and Essential Oils. Essential oils are flammable. It's safest to avoid making or using dryer sheets scented with essential oils.
I've heard about putting a few drops of lavender (or other) essential oil on a washcloth and tossing it in the dryer with your clothes. And I was.