Avoid them! And beware of eating foods that contain furocoumarins if you plan to go outside. Furocoumarins (psoralens) and derivatives are found in many plants. Psoralens are chemicals found in many plants, like fig, celery, parsley, parsnip, lime, lemons and clove, and some fungi.
These chemicals are natural and can be deadly, they are potent plant defenses against insects …and us.
Crazy fact: psoralens was used in tanning accelerators until 1996! Never mind that it can lead to skin cancer or skin loss.
However dangerous, they can be useful when used by experts. Seeds of Psoralea corylifolia were used hundreds of years ago in India for repigmentation in vitiligo patients.
How do they work?
Following UVA activation at 365 nm. either the furan or the pyrone side of psoralen crosslinks with pyrimidine bases and lead to DNA mutation. Photoactivated psoralens can also generate free radicals, and react with lipids and proteins.
Phytophotodermatitis is a skin eruption that occurs after contact with photosensitizing compounds in plants and exposure to UV light. There are two common presentations of phytophotodermatitis. Erythema and vesicles similar to those caused by severe sunburn come first, and after the inflammation resolves, the damaged skin stays hyperpigmented.
An experienced MD may use psoralens as a tool in treating psoriasis and pre-cancerous lesions (PUVA therapy) but remember: powerful tools must be left to those who have the knowledge to use them.
Beware of products containing plant extracts known to contain psoralens. They can be processed to remove psoralens but make sure that you are buying from a reputable company.
Wu S, Han J, Feskanich D, et al. Citrus Consumption and Risk of Cutaneous Malignant Melanoma. J Clin Oncol. 2015;33(23):2500-2508. doi:10.1200/JCO.2014.57.4111