Provided is a method of determining a concentration (Ca) of a first analyte (a) in sweat excreted by a first sweat gland type at a first skin location (i) having the first sweat gland type and a second sweat gland type. The method comprises measuring a first concentration Cai of the first analyte in sweat excreted at the first skin location and measuring at least one parameter relating to sweat excreted by the second sweat gland type at a second skin location (ii) having the second sweat gland type but not the first sweat gland type. The at least one parameter is used to determine a dilution factor Dai which quantifies dilution of the first analyte by sweat excreted by the second sweat gland type at the first skin location. This dilution factor Dai is then used to correct the first concentration Cai so as to determine the concentration (Ca). Further provided is an apparatus (100) for determining the concentration (Ca).
