Aromatherapy is a holistic treatment which uses concentrated oils from plants, called essential oils or fragrances. They must be diluted in water before use. They should not be poured directly on the sauna stones, because that could pose a fire hazard. You can use special infusion stones or aroma bowls, made of ceramic or stainless steel. As the rock tray heats, the oil evaporates in to the air dispersing the pleasing fragrance in the sauna.