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- In an ingrown toenail, the distal margin of the nail plate grows into the lateral nail fold, causing irritation, inflammation, and sometimes bacterial or fungal infection:
- Stage 1 (inflammation): erythema, edema, tenderness to palpation of lateral nail fold
- Stage 2 (abscess): increased pain, erythema, and edema as well as drainage (purulent or serous)
- Stage 3 (granulation): Chronic inflammation leads to further erythema, edema, and pain, often with granulation tissue growing over the nail plate and significant nail fold hypertrophy.
- Can reoccur
- Synonym(s): onychocryptosis, unguis incarnatus
- Great toenail is most often affected.
- Lateral edge of nail is more commonly affected than the medial edge.
- Most common in males aged 14 to 25 years
- Infrequent, but more often in elderly females than in elderly males
- More common in those with lower incomes
- 24.5/1,000 overall
- 50/1,000 ≥65 years
Etiology and Pathophysiology
- Nail plate penetrates the nail fold, causing a foreign body reaction (inflammation).
- Bacteria or fungi may enter through the opening in the nail fold, causing infection and abscess formation.
- The inflamed and infected area leads to granulation tissue and hypertrophy of the nail fold.
- Genetic factors
- Increased nail fold width
- Decreased nail thickness
- Medial rotation of the toe
- Many others proposed; none proven, including the following:
- Distorted, thickened nail (onychogryphosis)
- Fungal infection (onychomycosis)
- Improper trimming of the lateral nail plate
- Poorly fitting shoes
- Trauma to nail or nail fold
- Conditions that predispose to pedal edema (i.e., thyroid dysfunction, diabetes, obesity, heart failure, renal disease)
- Properly fitting shoes
- Proper nail trimming (see “Patient Education”)