Distinguish between continuous and pulsed currents regarding tissue response and safety.

• A. Continuous currents are safer than pulsed currents.
• B. Pulsed currents cause less selective activation.
• C. Continuous currents are less likely to cause polarization.
• D. Continuous currents can cause polarization and skin irritation; pulsed currents deliver discrete bursts, reducing side effects and enabling selective activation.

Answer: (D)

Continuous current causes a steady flow of charge that builds up at the electrode–skin interface, leading to polarization. This buildup shifts the local electric field, drags ions to the surface, and can cause chemical changes (pH shifts), skin irritation, and even burns if the current is strong or contact is poor. The constant energy also increases the likelihood of tissue heating.

Pulsed currents deliver the charge in short bursts with off times in between. The off periods allow charge to dissipate and ions to diffuse away, greatly reducing polarization, chemical buildup, and skin irritation. Because the stimulation happens in discrete packets, you can adjust pulse duration, amplitude, and frequency to target different nerve fibers, increasing the chance of selective activation while keeping safety margins—heating and tissue stress stay lower due to the intermittent nature of the delivery and the typically limited net charge per phase.

That combination—less polarization and reduced side effects with the ability to tailor activation—explains why pulsed currents are often safer and more versatile for tissue stimulation.