For dermal absorption, the study of measurement in depth concentration
profiles of a number of different nickel salts in the stratum corneum of human
volunteers found the nickel salts of acetate, nitrate, sulfate, and chloride can cause
penetration as a function of the counterion from high to low respectively (Hostynek et
al., 2001). Another case studied human skin under occlusion and penetration of Ni2+
ion from NiCl2 via the skin. The results found that Ni2+ from NiCl2 can occlude and
penetrate 0.23% when applied dose after 144 hours and 40–50 times quicker than
from NiSO4. If without occlusion, NiCl2 can penetrate reduce more than 90% and not
found absorption when used NiSO4. However, these results are in agreement that
under occlusion using NiCl2 rather than NiSO4 were probably to produce a positive
reaction in nickel-sensitive patients (Fullerton et al., 1986).