Incidentally, the “celery tacos” is an obscure reference dedicated to mothers and grandmothers of children 2-5 years old who watch Wonder Pets.
Some plants, like lime, lemon, celery and many others, contain chemicals called furocoumarins that absorb UV radiation. If a product containing this chemical is applied to the skin, UV will start a chain of chemical reactions that can damage the skin severely. The phototoxic inflammatory eruption usually appears 24 hours after exposure and peaks within 48-72 hours. Initial burning erythema is followed by blistering, epidermal necrosis and desquamation. Hyperpigmentation is one the the long-term effects.
Furocoumarins absorb UV-A (320-380 nm) light enable furocoumarins, increasing the energy state of the molecule and its reactivity. This excess energy will be dissipated in a variety of ways, e.g. forming photoaddition products with DNA and resulting in mutations of epidermal nuclear DNA and damage to lipids in the cell membranes.
This property of furocoumarins, also called psoralens, can be used for medical purposes, in what is called “photodynamic therapy” of skin problems like vitiligo, psoriasis, cutaneous T-cell lymphoma (CTCL), alopecia areata and eczema.
Continuing with the thread of “what you don’t know can hurt you”, some essential oils and fragrances contain psoralens. Applying an essential oil containing psoralens will not hurt your skin unless you are also exposed to UV. Oil of bergamot, extracted from the rind of fresh bergamot oranges (Citrus bergamia), is commonly used to scent commercial perfumes and colognes. Use of such oils and fragrances is not allowed in Europe, but it seems that some “herbal products” that promise accelerated tanning do contain these chemicals, and here we go again with the use of “natural” as if it were synonym of goodness.
I will add a few items to the list of plants to avoid if you are going to be in the sun: figs, parsley, hair lighteners containing citrus oil, lime juice (Margaritas!), natural and synthetic geranium fragrance,
Maybe I should also write to the Wonder Pets regarding the danger of eating celery tacos on the beach?