In order to diagnose nail fungus infections, a doctor will usually examine debris that is scraped from underneath the nail. The nail scrapings will be used in tests, such as a potassium hydroxide (KOH) smear, or a fungal culture. The KOH test can be quickly performed, while the fungal culture can take weeks. Physicians must be careful when diagnosing fungal infections of the nail because several other conditions can result in similar symptoms. These include psoriasis, lichen planus, contact dermatitis, trauma, nail bed tumor, eczema, and yellow nail syndrome.

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