Not applicable. This is a manual tool, not a topical product.
Source: Scholl product information.

Use the coarse side on dry or slightly damp hard skin with light, even strokes, then finish with the fine side to smooth. Work gradually rather than removing everything in one session. Rinse and dry after use.

Two sided: coarse for removal, fine for smoothing
Finishes the skin rather than leaving it rough
Hygienic and durable
No batteries or replacement parts
For external use on feet

For external use on feet only. Not for use on broken, cracked, irritated or inflamed skin, or over open wounds, moles or warts. Do not over-file - remove hard skin gradually across several sessions. Keep out of reach of children. If you have diabetes, poor circulation or reduced sensation in your feet, do not use without first speaking to your doctor or podiatrist. Discontinue use if the skin becomes sore.