Foodstuffs are an uncommon cause of immunologically mediated contact dermatitis, although regular contact with vegetables and meat can certainly irritate intact or eczematous skin. Plant-derived saps such as from poison ivy and poison oak can cause a characteristic contact dermatitis. There exists cross-reactivity with these saps and mango skin and the oil from cashew nut shells.
Some clinicians claim an exacerbation of eczema/atopic dermatitis in patients who are patch test positive to nickel, cobalt and balsam of Peru, following oral ingestion of foods containing these substances. They similarly claim an improvement in these patients' conditions when they manipulate their diet to reduce the amount of these substances. There is some double-blind placebo-controlled evidence to support this, although there are some problems with the study design, in particular with the amount, source and form in which the salts are ingested. An exacerbation of eczema following oral ingestion of foods to which patients are patch test positive is not a commonly accepted view.28
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