Thank you for your post. I have never heard of this technique for allergies but I am intrigued. However, I see one problem with your plan: your TENS unit more than likely delivers biphasic pulsed current. Because iontophoresis is predicated on creating a unidirectional electrical field to move the medicinal ion, a biphasic current will not create the "pushing" force you need to perform iontophoresis. Iontophoresis traditionally uses direct current and maybe monophasic pulsed current (and I have even seen a biphasic current with a DC offset-- but rare). With a balanced biphasic pulsed current there is not a sustained anode or cathode as the (+) and (-) poles switch at whatever frequency rate you have selected. That being said, a clinical iontophoresis device (typical peak amplitude 4-5mA) will deliver direct current and would provide the 'push' you need to move the ion.