Which property of monophasic currents may cause polarization and skin irritation?

• A. Monophasic currents deliver net charge causing polarization and skin irritation.
• B. Biphasic currents deliver net charge causing irritation.
• C. Biphasic currents are always balanced like DC.
• D. Monophasic currents deliver net charge causing polarization and skin irritation; biphasic currents are charge-balanced, reducing net charge and improving comfort and safety.

Answer: (D)

The key idea is how net charge and polarity changes affect tissue response during electrical stimulation. Monophasic currents flow in one direction for a portion of the cycle, creating a net charge at the electrode–tissue interface over time. That net charge causes polarization of the tissue, which can lead to discomfort and skin irritation as ions accumulate at the skin surface and beneath the electrode, and can even drive chemical changes at higher intensities.

In contrast, biphasic currents reverse polarity within each cycle, so the charges cancel out over time. This charge-balanced nature means there’s little or no net charge accumulating at the interface, which minimizes polarization, reduces ion buildup, and generally improves patient comfort and safety.

So, monophasic currents have the potential to cause polarization and skin irritation due to a net charge, while biphasic currents are designed to be charge-balanced, reducing net charge and enhancing comfort and safety.