In candle making, sweating refers to beads of liquid oil appearing on the surface of a candle. It is caused by the expansion and contraction of wax crystals, which can squeeze oil out of the body of the wax, making it visible on surfaces.

There are many reasons why a candle may have liquid on the surface. The first is that there may simply be too much fragrance or essential oil mixed into the wax. This means that there is insufficient space between the crystals to retain the amount of fragrance oil added. Second, sweating may be a characteristic of the wax itself. Many plant waxes are a blend of fully and partially hydrogenated oils. If cooled incorrectly (too slowly), low melt point ‘alpha’ crystals can form and sit on the surface of the wax as a liquid or slurry. These fat oils can also displace fragrance oils, as there is insufficient space for additional liquids amongst the crystals. Third, rapid changes in temperature can cause sweating, especially when moving a candle from a cold location to a warm location. This can also happen if the oil is added when the wax is too cool, or if the wax/oil is not properly mixed. In this instance, the wax and oil do not form a homogenous mixture and the distribution of fragrance will vary throughout the candle. Finally, if the fragrance supplier has little experience in candles, their fragrance oils may contain components that are insoluble in your wax. This can be the case when fragrances were developed for other products (i.e. cosmetic products), as fragrances do not always perform well in multiple products and should be fine-tuned for the end application.