Some essential oils contain furanocoumarins. These organic chemical compounds can cause phyto-photo-dermatitis, which is the skin’s hypersensitivity to the UV rays of sunlight. Possible skin reactions include stinging, itching, blisters and burning.
When using essential oils on the skin, it is important to either avoid using furanocoumarin oils or avoid exposure to the sun for at least 24 hours after application of oils.
Some essential oil references simply state that citrus oil are photo-toxic. More specifically, essential oils from some plants in the Umbelliferae (Parsley) and Rutaceae (Citrus) families need to be avoided.
The following chart shows which oils are safe to use and which should be avoided during sun exposure.