Have you ever heard of Margarita Burn? If so, that’s Phytophotodermatitis. Its the reason we shouldn’t use lime juice in our henna paste.
Some botanical compounds can react with UV light, changing them them into something toxic to skin and creating burns. The intensity of burns varies depending on sensitivity, and the amount of exposure to both the plant matter and sunlight. The symptoms can range from slight itching and burning with a bruise like appearance or browning of the skin, to extreme discomfort and blisters. Symptoms usually don’t show until the day after exposure.
Plants that can cause this reaction are:
Several species of wild flowers (umbelliferae).
Some sources will list citrus in general, but after much searching I found actual reports of citrus burns to be almost exclusively lime, with the occasional grapefruit report. The photo below is burns caused by lime juice.
Many professional artists concerned about this issue or general citrus allergies have chosen to reduce the amount of lemon in their paste or move to non-lemon mixes. Personally, I’ve been using just a small amount of lemon diluted in water. It is, however, very clear that we should never use lime or grapefruit juice for henna paste!
The following links will provide more information: