Not applicable. This is an electrical device, not a topical product.
Source: Scholl product information.

Glide the roller head over hard skin using light pressure, keeping the device moving rather than holding it in one spot. Can be used on wet or dry skin. Stop as soon as the skin feels smooth. Clean the roller head after each use and replace it about every three months.

Removes very hard skin and smooths in one device
Can be used wet or dry
Powered, so results are more even than a manual file
Replacement roller heads available separately
Part of the Scholl ExpertCare range

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 rather than in one. 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 or irritated.