Slide show: How to trim thickened toenails
Image of thickened toenails
Previous Next 1 of 5 Thickened toenails: What causes them?

Your toenails can thicken for many reasons. These include:

  • A common skin condition that causes cells to build up rapidly on the surface of the skin (psoriasis)
  • Injury
  • Tight-fitting shoes
  • Fungal infections — as shown in this picture

Among these, a fungal nail infection — onychomycosis (on-ih-koh-my-KOH-sis) — is a common cause of thickened toenails.

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See more Multimedia July 11, 2020