Objectives: The executive committee for treatment guideline of onychomycosis of in Korean society for medical mycology is aimed to provide an up-to-date, practical, algorithmic guideline for the management of onychomycosis in Koreans. 
Methods: The executive committee thoroughly reviewed thoroughly relevant literatures collected on MEDLINE, PUBMED, EMBASE, RISS, and Google scholar. Then, the structured algorithm was developed through a full discussion, robust agreement between members, and, ultimately, voting on the conflicting subjects.
Results: The presence of clinical signs such as yellow discoloration or thickening of the nail, onycholysis, is highly predictive; however, mycological examination (i.e. KOH, fungal culture, histopathological analysis) should be done to confirm clinical suspicion of onychomycosis and rule out other nail disorders before starting the treatment. Simple noninvasive dermoscopy can enhance clinician’s diagnostic accuracy and allow determination of the best site for adequate sampling. Various therapeutic options are available for onychomycosis and the mainstays of the therapy are topical and systemic antifungal agents. Currently, there are available antifungal agents in Korea that include oral terbinafine, itraconazole, fluconazole and topical efinaconzole, ciclopirox, amorolfine. Factors that may influence the selection of topical versus systemic therapy are the nail variables (clinical subtype, disease severity), patients’ variables (underlying medical illness, drug-drug interactions). Although systemic agents yield better cure rates, there has been a great emphasis on the development of topical agents as they have fewer side effects and drug interactions. For mild cases (DLSO <50% nail involvement, SWO), both systemic and topical therapy can be an option, whereas systemic therapy is a treatment choice for moderate-to-severe cases (>50% nail involvement of DLSO, PSO, TDO, dermatophytoma, spike, subungual hyperkeratosis >2mm) if there are no contraindications to systemic antifungal agents. Oral terbinafine is the first-line medication for dermatophyte infection; however, it may be changed depending on the causative fungi. Combination treatment of topical and systemic antifungal agents is recommended to increased efficacy in severe cases. Adjuvant treatments, physical or chemical removal of the involved nail, are typically reserved for patients who cannot be successfully treated with medical treatment alone. Alternative treatments includes laser therapy (Nd:Yag or diode laser) or photodynamic therapy. They can be performed when standard medical treatments cannot be applicable regardless of the severity of onychomycosis. Currently, lasers are only approved for temporary cosmetic improvement of the nail on onychomycosis. During the treatment period, proper evaluation of treatment response at 3, 6, 12, 18 months after the completion of the treatment should be rendered. After a patient has achieved effective cure (<10% of nail involvement and mycological cure in the clinical setting), patient’s education for prevention is recommended to minimize reinfection or recurrence.
Conclusion: The Korean consensus guideline for onychomycosis is designed to promote the assessment and treatment of onychomycosis. We hope that this new guideline will serve as the standard for many years to come on the topic of onychomycosis.

Korean Guideline for the diagnosis and treatment of onychomycosis: A Consensus Update by Korean Society for Medical Mycology