Sweat is stimulated and collected from the eccrine sweat glands in the lower inner volar surface of the forearm using the drug pilocarpine, as shown in the images on the right. The skin should be free of rashes, cuts, and inflammation, which could contaminate the sweat with serous fluid. Pilocarpine is a cholinergic drug, which is delivered to the sweat glands via iontophoresis. Pilocarpine is positively charged and is delivered transdermally into the sweat glands using a small current from the positive electrode. A negative electrode is placed over an electrolyte material to complete the circuit. The pilocarpine and electrolyte solutions are either placed on gauze pads for stimulation (upper image on the right) or are available as pilocarpine gel discs (lower image on the right). The arm is carefully cleansed with distilled water prior to stimulation. Iontophoresis lasts for about 5 minutes at a current ranging from 1.5-3.5 mAmps, depending on the instrumentation. Generally it is well tolerated and feels like a slight tingling sensation. After five minutes, the skin is again carefully cleansed with distilled water and dried thoroughly prior to collection.
Skin reactions such as burns or urticara during iontophoresis are rare, but require documentation, medical attention for the patient, and appropriate disinfection of equipment. Sweat must never be collected over a burn or rash.