Infections of the nail plate or sub nail tissue caused by various fungi are collectively referred to as nail fungal diseases and are common in dermatology. With an aging population, social interactions and an increasing number of patients with immune compromised hosts such as tumors, autoimmune diseases, organ transplants, diabetes, and AIDS, fungal infections are on a continuous clinical rise. At the same time, the species of fungal pathogens are also changing. 1, etiology Mainly caused by dermatophyte infections, followed by yeast and non-dermatophytic mycobacteria. Dermatophytes include Trichophyton rubrum, Trichophyton sudangii, and Trichophyton flocculentum epidermidis, with Trichophyton rubrum taking the lead. Recently, it has been reported that Trichophyton sudanicum is the causative agent of the intra-nail type infection; yeasts are mainly Candida, Malassezia, etc. Occasionally, two or more pathogenic fungi may coexist on the same diseased nail. The susceptibility factors include genetic factors, hyperhidrosis of the hands and feet, systemic diseases (such as diabetes, AIDS), long-term application of corticosteroids or immunosuppressants, local blood or lymphatic fluid reflux disorders, wearing impermeable shoes and socks, certain professionals (such as bathroom staff, athletes, etc.), nail trauma or other nail diseases, etc. 2. Clinical manifestations Nail fungal disease accounts for about 30% of dermatophytosis, while about 50% of patients with tinea capitis have nail fungal disease, and the prevalence increases with age. The clinical features of nail fungal disease include thickening, discoloration, and lack of luster of the nail plate, separation of the nail plate and nail bed, hollowing, buckling, and unevenness of the nail plate. According to the different parts and degrees of fungal invasion of the nail, it can be divided into the following types: ① White superficial type: rare. The pathogenic fungus invades directly from the surface of the nail plate. The nail plate surface loses its luster or is slightly uneven. The white spots are the size of a pinpoint and can expand or fuse, involving the entire nail plate. The common causative agent is Trichophyton rubrum. ② Distal lateral subxiphoid nail type: the most common. It mostly spreads from tinea pedis. The fungus invades the distal anterior and lateral edges of the nail from one side of the nail bed and causes thickening, grayish-yellow turbidity, and uneven or broken nail surface. The causative organism is mostly Trichophyton rubrum, followed by Trichophyton rubrum. (3) Subproximal nail type: less common. Most of them enter the nail plate and the nail bed through the nail tubercle. The nail is rough, thickened, uneven or broken at the nail root and half moon. The causative agent is mostly Trichophyton rubrum. ④ Total nail destruction type: It is the final result of the development of each type of nail fungal disease. The whole nail plate is destroyed, grayish yellow or grayish brown, the nail plate is partially or completely lost, the surface of the nail bed remains rough keratinized accumulation, the nail bed can also be thickened, flaking. There are six special types of nail fungal disease: ① Severe nail separation type: fungal infection from the nail bed to the nail plate, the nail bed and nail plate separation is serious. ② Lateral edge type nail fungal disease. ③Dermatophytoma: Dermatophytoma is a dense mass composed of keratinous material and fungal components. Dermatophytoma is located between the nail bed and the nail plate. ④ nail fungus with longitudinal pattern formation: longitudinal pattern implies the formation of longitudinal tunnels in which keratinous and fungal components are present, with swelling of the nail bed around them and poor drug penetration. ⑤ Nail fungal disease with nail hemimelia involvement. (6) Nail fungal disease with severe nail plate thickening: nail plate thickness > 2 mm. the drug concentration of systemic medication may not reach this value in the dorsal nail plate. In addition, nail fungal disease can be divided into nail fungal disease caused by dermatophytes, nail fungal disease caused by yeasts and nail fungal disease caused by molds, according to the type of pathogenic fungus invaded by the diseased nail. Histopathology The fungus can be easily found by PAS staining of the nail of onychomycosis, and the mycelium and arthrospores can be seen in the nail plate layer, usually confined to the lowermost part of the nail plate. Nail luxation is generally not a feature of dermatophyte infection, except that the nail plate may be mechanically separated by the fungus growing between it, and the distribution and number of fungi within the nail plate varies. The tissue beneath the nail plate may be completely free of inflammation or have only a minimal inflammatory response. In fungal leukoplakia, the fungal hyphae are confined to the uppermost part of the nail plate and rarely spread to deeper layers, but a large number of hyphae can be seen in the upper part of the nail plate, which are larger and wider than those seen in subdermal onychomycosis. There are often clumps of swollen hyphae and irregularly shaped arthrospores in the cuttings. In short broomstick nail fungal disease, conidia can often be found in the nail. Candida nail fungal disease can be accompanied by chronic nail sulcus, other yeast caused by the nail sulcus and nail bed in the debris, sections can be seen in which there are mycelium. 4, diagnosis and differential diagnosis clinical diagnosis based on nail discoloration, lusterless, thickened and broken, combined with positive fungal microscopy can confirm the diagnosis. However, if there are conditions, fungal culture or multiple fungal culture or multi-point inoculation method fungal culture should be done. Differential diagnosis of this disease and nail dystrophy, psoriasis, lichen planus, chronic eczema, erysipelas, continuous limb dermatitis and other causes of nail disease and nail warts, nail tumors, etc. to distinguish. 5.Treatment For nail fungal disease, oral or topical treatment can be used. Oral drugs reach the nail plate through the nail matrix and nail bed; topical drugs reach the nail bed through the nail plate. Oral medications are more likely to enter the nail matrix and nail bed, while topical medications are more likely to treat infections at the dorsal nail plate. Chemical nail removal therapy is the process of applying keratin stripping drugs to remove the nail plate. Domestic use of 4o% urea ointment for nail fungal disease for chemical nail removal therapy, the total efficiency of about 50% to 60%. The disadvantage is that the adverse reactions are more serious, affecting life and work, and the recurrence rate is high. Generally only used for superficial infection site, a single nail infection area.