Photosensitive: having a chemical, electrical, or other response to light.
You might be wondering “what does photosensitive have to do with essential oils?”. Certain medications (including antibiotics) can increase the skin’s reaction to UV rays. In the same vein, some essential oils also contain chemical components that may cause what is known as “photosensitivization” when applied to the skin before sun exposure.
Remember that just because something is “natural” doesn’t mean it can’t harm you. A quick Google Image Search for “essential oil burns” will show you more than you’d ever hope to see, but the take away is this: use essential oils, especially phototoxic ones, with discretion. Essential oils are extremely concentrated and have their own unique chemical make-up. While not all oils are created equal, a good rule of thumb is to avoid using citrus oils (especially Bergamot) before heading out into direct sunlight.
If you do happen to use a potentially phototoxic essential oil, or a blend containing one, cover the area of skin where the oil was applied. Keep it out of direct UV light (sunlight or tanning beds) for at least several hours, possibly up to 12-24 hours. Head out into that summer sun safely and with confidence!