The oils of aromatic plants have been used for centuries for both their smell and their medicinal applications. But just because something is natural doesn’t mean it’s good for you. Essential oils are powerful chemical compounds. They may smell wonderful but they need to be used (both by you, the soap and candle maker and by the people who will be using your soaps and candles,) carefully and conscientiously. All essential oils must be used with care, but here are 5 categories of essential oils that need to be used with extra care.