A sweat sensing device (28) includes a plurality of sweat collection pads (40, 42, and 44) communicating with a sensor (36). Each of the pads (40, 42, and 44) is activated by electronics (34) that include a timing circuit which allows one or more of the pads (40, 42, and 44) to be activated at a selected time and subsequent deactivated after a defined period of time. This allows for selective collection of sweat from a plurality of pads over a prolonged period of time. Further, the devices can use a common microfluidic device (38) which both transports sweat activating substance, such as pilocarpine, to the surface of the skin (12) and directs sweat away from the skin (12) to a sensing device (28).
