Figure 1. Association of sweat Na ⁺ concentration with skin Na ⁺ and age Association of sweat Na ⁺ concentration with skin Na ⁺ and age.

Tissue Na⁺ concentration in the skin and age are positively correlated with sweat Na ⁺ (ρ = 0.302, P = 0.019 and ρ = 0.341, P = 0.002, respectively; linear regression lines are depicted in red). Red X = automatically identified outliers (ROUT = 1%); after their removal, statistics revealed ρ = 0.367, P = 0.001 and ρ = 0.345, P < 0.01, respectively.