Fungal Nail Infection (Onychomycosis)
Fungal nail infection (onychomycosis) is a chronic nail-plate infection, managed per the AAFP Rapid Evidence Review and an expert US therapeutic consensus panel.
Symptoms
Thickened, discolored (yellow, white, or brown), and crumbly nails, most often on the toenails, sometimes with nail separation from the nail bed.
Causes and risk
Dermatophyte fungi, usually spreading from an existing athlete's foot infection; risk rises with age, diabetes, poor circulation, nail trauma, and shared damp environments like locker rooms.
How it is evaluated
Laboratory confirmation (KOH, culture, or PCR) is recommended before starting oral treatment, since the differential includes psoriasis, trauma, and rarely malignancy.
Treatment
Oral terbinafine is first-line, outperforming topical and other oral options for cure rate, per Cochrane and network meta-analysis data; a baseline liver function check is recommended before starting. Topical options suit milder or thinner-nail cases. Full nail regrowth can take up to 12-18 months for toenails.
When to seek care
Signs of spreading infection, or nail changes in someone with diabetes or peripheral vascular disease (where complications can become limb-threatening), warrant prompt evaluation.