Nickel is one of the most common causes of contact skin allergy, but can consumption of foods containing nickel actually cause a contact dermatitis to occur? And since nickel in foods is not in direct contact with the skin, what is the mechanism for this to occur?
Nickel is ubiquitous in nature, and occurs in soil and in many different foods at varying concentrations. Some of the higher nickel containing foods include legumes, whole grain flour, oats, soybean, shellfish, fish, certain vegetables tea, cocoa, licorice, chocolate, potatoes, and foods in cans or cooked in nickel utensils.
Proof that eating large amounts of these foods could cause a skin reaction is certainly lacking. Over the years, there have been many anecdotal reports, such as the one published recently in the journal Pediatric Dermatology, entitled "Easter Egg Hunt Dermatitis: Systemic Allergic Contact Dermatitis Associated with Chocolate Ingestion," that would suggest this can occur. But the few clinical studies that have been done have required ingestion of massive amounts of nickel.
Moreover, there have been no long-term randomized blinded trials to confirm that ingestion of nickel containing foods can cause exacerbation of symptoms. In fact, the mechanism by which a "systemic" contact dermatitis developing as a result of ingestion of a food or mineral is unknown, and somewhat implausible. Most experts in the field are skeptical of this phenomenon, because of this lack of evidence based studies. In other words, people can indeed be sensitized to nickel, and they may be consuming foods with high levels of nickel, but the two are probably unrelated and it is difficult to identify any causal relationship.
Patients who are sensitized to nickel may develop a rash on areas where there skin has been in contact with nickel, including items such as jewelry, watch bands, metal tools, dyes, keys, insecticides and many other household or professional items. Nickel is also found in most alloys, and it is even added to gold to render it harder. Thus, anything under 24K gold contains a certain amount of nickel. One of the more recent "modern" consequences of nickel allergy includes the development of a contact allergy skin rash on the face or ear as a result of direct and persistent contact with cell phones.
The reports of nickel in foods causing a contact dermatitis are rare enough that the average nickel-allergic person does not have to take any specific precautions during Easter. Those who experience adverse effects of binging on nickel containing foods including chocolate during Easter should avoid doing this, if not for contact dermatitis, then for other health reasons as well.