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

Glide the file over dry or damp hard skin using light pressure. Work gradually rather than trying to remove everything at once. Rinse and dry after use.

Nano glass surface buffs hard and rough skin evenly
Designed for one-handed use
Washable, durable and reusable
No replacement heads or batteries needed
Compact enough to travel with

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.