Infections of the nail plate or nail tissue caused by various fungi are collectively called nail fungus (onychomycosis), while onychomycosis (tinea unguium) refers specifically to nail infections caused by dermatophytes. Etiology】 It is mainly caused by dermatophyte infection, followed by yeast and non-dermatophyte mycobacteria. Dermatophytes include Trichophyton rubrum, Trichophyton spp. and Flocculina epidermidis, of which Trichophyton rubrum occupies the first place, recently reported Trichophyton sudanense (T. soudanense) is the causative agent of nail infection; yeast is mainly Candida (Candida), Malassezia (Malassezia); other molds include columnar spore mold (Scytalidium), Short broom mold (Scopulariopsis brevicaulis), etc. Dermatophytes can break down keratin and produce invasive enzymes to invade and destroy normal tissues, leading to primary nail infections. Secondary nail infections mostly occur after the nail is damaged by certain factors, mostly caused by yeasts and molds that do not have the ability to break down keratin. The same diseased nail can occasionally be infected with two or more pathogenic fungi. Nail fungal disease is mostly transmitted directly by tinea pedis, and susceptibility factors include genetic factors, systemic diseases (such as diabetes), local blood or lymphatic fluid return disorders, nail trauma or other nail diseases, etc. Clinical manifestations】 Nail fungal disease accounts for about 30% of dermatophytosis, and about 50% of patients with tinea capitis have nail fungal disease, and the prevalence increases with age. Depending on the location and degree of fungal invasion of the nail, it can be divided into the following types (Figure 11-4), (a) superficial white onychomycosis (SWO) caused by direct invasion of the causative fungus from the surface of the nail plate. It appears as dotted or irregular white clouding of the superficial nail plate, and the nail plate surface loses its luster or is slightly uneven. (2) Distal and lateral subungual onychomycosis (DLSO) is the most common type, mostly caused by the spread of tinea pedis. The fungus invades the distal anterior and lateral edges of the nail from one side of the nail contour and causes thickening, grayish-yellow turbidity, and uneven or broken nail surface. (C) Proximal subungual onychomycosisi (PSO) Mostly through the nail dermis and into the nail plate and nail bed. The nail is rough, thickened, uneven or broken at the nail root and half-moon. (D) Total dystrophic onychomycosis (TDO) is the final result of all types of nail fungal disease. The whole nail plate is destroyed, grayish yellow, grayish brown, partial or complete loss of the nail plate, the surface of the nail bed remains rough keratinized accumulation, the nail bed can also be thickened, flaking. In addition to the above types, there is also an intra-deck type, which is rare. It is mainly caused by Trichophyton sudanum. The fungus invades the entire nail plate, but does not progress downward. There is no hyperkeratosis or separation of the nail. The disease is slow and can last a lifetime if left untreated. There are usually no conscious symptoms, but thickening or destruction of the nail plate may affect the fine finger movements. Occasionally, nail infections may occur secondary to nail fungus, with redness, swelling, heat and pain. Diagnosis and Differential Diagnosis】 The diagnosis can be confirmed based on nail discoloration, lack of luster, thickened and broken, combined with positive fungal microscopy, and fungal culture if necessary. The disease needs to be differentiated from nail dystrophy, psoriasis, lichen planus, chronic eczema and other nail diseases and nail warts, nail tumors, etc. Prevention and treatment】 Because the drug is not easy to enter the nail plate and nail growth is slow, so the treatment is more difficult, the key is to adhere to the medication. 1, topical drug treatment commonly used in superficial and not involving the nail root of the damage. First, remove the diseased nail as much as possible with a knife or nail file, and then apply 30% glacial acetic acid solution or 3% to 5% iodine tincture twice a day for 3-6 months until the new nail is produced; 40% urea ointment can be used to soften and peel the diseased nail, and then topical antifungal preparations; 8% ciclopirox, 5% amorolfine nail coating can form a drug film on the nail surface to facilitate the penetration of drugs into the nail plate. Surgical nail extraction is painful and damaging, and is rarely used at present. 2, internal drug treatment Available itraconazole intermittent shock therapy (400mg / d, divided into 2 oral, 1 week per month for a course of treatment), nail involvement requires 2-3 courses, toenail involvement requires 3-4 courses; also available terbinafine 250 mg / d oral, nail involvement course of 4 weeks, toenail involvement course of 6 weeks. Combination with topical drugs can improve the efficacy.