Nickel is a very common metal contained in many everyday objects and is the 
leading cause of ACD (Allergic Contact Dermatitis). Nickel is present in most of 
the constituents of a normal diet, but some food groups are usually considered 
to be richer. However, the nickel content of specific food can vary widely, 
depending on many factors. Thus, the daily intake of nickel is also highly 
variable both among different populations and in a single individual, in 
different seasons and even in different days. Measuring precisely the daily 
intake of nickel from food and drinks is extremely difficult, if not impossible. 
The relationship between ACD and contact with nickel is undisputed and widely 
confirmed in literature. The situation is different for systemic nickel allergy 
syndrome (SNAS). The SNAS can have cutaneous signs and symptoms (Systemic 
Contact Dermatitis or SCD) or extracutaneous signs and symptoms 
(gastrointestinal, respiratory, neurological, etc.).The occurrence of SCD as a 
systemic reaction to the nickel normally assumed in the daily diet is very 
controversial. A rigorous demonstration of the relationship between SCD and 
nickel is extremely difficult. In particular, further and larger studies are 
needed to assess the reality and the prevalence of nickel urticaria. With 
respect to nickel-related gastrointestinal symptoms, as well as chronic fatigue 
syndrome, fibromyalgia, headache, recurring cold sores and recurrent infections 
in general, the data available in literature are not conclusive and the studies 
lack the support of clear, first-hand evidence. With respect to respiratory 
disorders, the role of food nickel and the effectiveness of a dietary treatment 
have been assumed but not proven. In fact, the usefullness of a therapeutic 
low-nickel diet is controversial: rare, if not exceptional, and limited to very 
sporadic cases of SCD. Additionally, the quantitative and qualitative 
composition of a low-nickel diet presents few certainties and many 
uncertainties. The low-nickel diets suggested in literature are highly variable, 
both in the extension of the restrictions and in their details--and the 
differences are not marginal.
CONCLUSION: an evaluation of the data presented by medical literature about SNAS 
and its relationship with oral nickel does not allow to draw final conclusions. 
In the absence of genuine certainty we can only conclude that further and 
broader studies, more rigorously conducted, are needed.