serenspec
frenz headband (it can measure deep sleep…)
Good question, and you’re right that 4mA tDCS head limits don’t translate directly — but the hand situation has a specific danger the head doesn’t:
Current Path is Everything
Hand-to-hand = crosses the chest/heart. This is the dangerous configuration:
- ~10mA hand-to-hand can cause involuntary muscle contraction (“let-go” failure)
- ~100mA can induce ventricular fibrillation
- DC is worse than high-frequency AC for cardiac risk
Same-hand (e.g., finger-to-wrist) = much safer, current stays local
Safe Ranges by Modality
Application Typical Range Notes TENS (peripheral) 1–80mA High freq (>1kHz), feels like buzzing Galvanic skin stimulation 0.5–5mA DC, research use Peripheral nerve stim (research) 1–20mA Pulse width matters a lot “Uncomfortable but safe” <10mA DC Same-limb only Key Parameters Beyond mA
- Frequency: >1kHz dramatically reduces cardiac risk and pain
- Pulse width: shorter pulses (microseconds) = less charge per pulse
- Electrode size: larger = lower current density = less skin burning
- DC vs pulsed: pulsed is safer, DC causes electrolytic skin damage over time
Practical floor
For same-hand stimulation with TENS-style pulsed current, 1–20mA is well-studied territory. Are you building something custom or using off-the-shelf hardware? The delivery circuit matters as much as the current target.