Storing Essential Oils
Essential oils are perishable and should be stored in dark glass containers in a cool place. As the bottle empties, transfer the oil to a smaller bottle so the oil won't oxidize, causing decay. According to Marcel Lavabre's
Some essential oils contain chemicals that are photosensitizers. These substances can cause hyperpigmentation (brown spots) if worn directly on the skin in the sun. This is not a problem with soapmaking in general because the oil is washed from the skin. One photosensitizer is a chemical called bergaterpene, present in bergamot essential oil. If you are concerned, there are bergaterpene-free bergamot oils available.
Essential oils can be very expensive, so it is important that you store them properly. If you find you're making a lot of soap and using essential oils, it really pays to order from online suppliers. An essential oil that costs $8 per ¼ ounce in the health food store may cost only $40 a pound through an Internet soap supplier.