Nickel sensitization can not only induce allergic contact dermatitis (ACD), but 
also can induce an overlapping disease referred to as "systemic nickel allergy 
syndrome" (SNAS), characterized by urticaria/angioedema and gastrointestinal 
symptoms correlated to the ingestion of nickel-containing foods. This study was 
designed to determine if oxidative stress occurs in patients with nickel 
allergy. Thirty-one female patients (mean age 31.26 + 13.04 years, range 16-64 
years) with confirmed nickel CD underwent oral nickel challenge because of 
clinically suspected SNAS; serum concentrations of protein carbonyl groups 
(PCGs) and nitrosylated proteins (NPs; biomarkers of oxidative stress) were 
measured before and after oral nickel challenge as well as in healthy female 
controls. Twenty-three of these 31 patients were diagnosed with SNAS because 
they had a positive reaction to the oral nickel challenge, and 8 patients had no 
reaction and therefore were classified as patients with contact nickel allergy 
only. Although both nickel-allergic patients and controls presented similar 
serum levels of PCGs, NP values in nickel-allergic patients appeared higher than 
in controls and tended to decrease after the challenge; furthermore, serum 
levels of NPs in patients affected by SNAS were higher (although not 
significantly) than in patients with nickel ACD only. The involvement of 
specific biomarkers of oxidative stress such as NPs and the lack of involvement 
of other biomarkers such as PCGs may help to better understand the alteration of 
the redox homeostasis occurring in nickel ACD and particularly in SNAS.