Thank you for your inquiry.
As best I can tell, there is no literature whatsoever on photodermatitis related to the ingestion of peanuts or an increase in sensitivity to sun related to the ingestion of peanuts. Some foods upon contact with the skin can predispose to phototoxic reactions. They include parsnips, celery, mango peel, and lime juice. However, I could find no reports of or reference to the ingestion of any food (peanuts included) that produce this phenomenon.
Thus, there are only two possibilities to explain the reaction to the best of my knowledge. The first is that all of the patient’s observation of sunlight-induced rash is correct, but her attribution of cause and effect between the ingestion of peanuts and this rash is incorrect. The other possibility, of course, is that her observations could be valid and she could be having a reaction which requires both peanuts and sun to produce the lesions.
Since it is impossible to discern which of these two are correct, your only option, if you wish to pursue this issue, would be to perform an appropriate challenge. That is, perform a sunlight challenge with and without peanuts.
Thank you again for your inquiry and we hope this response is helpful to you.
Phil Lieberman, M.D.