Ichthyosis is a common hereditary keratosis of the skin, known in Chinese medicine as tinea cruris. It is clinically characterized by dry, rough, and markedly mottled skin on the extremities or trunk, with rhombic or polygonal scales and a fish scale or snakeskin-like appearance. There may also be high linearity of the palms of the hands and feet, hereditary allergies and intolerance of heat, or peri-hair keratosis. Depending on the mode of inheritance, they are classified as common ichthyosis, sex-linked ichthyosis, congenital ichthyosis-like erythroderma and lamellar ichthyosis. Ichthyosis vulgaris is the common type, and the genetic characteristics are considered to be a completely episodic autosomal dominant disease with no sex differences. The lesions are symmetrically distributed on the extensor side of the limbs and trunk, with the elbows and knees being the most prominent. The onset of the disease usually occurs within one year after birth and increases with age, with the most pronounced symptoms occurring during adolescence and then ceasing to develop. The lesions vary in severity, and in mild cases, the skin is only dry in winter, without obvious scales, and there is powder-like flakes after scratching, which is called dry skin disease. In severe cases, the lesions can spread to the whole body, accompanied by hyperkeratosis of the palms and plantars, cracking and finger (toe) nail changes. Generally, the face, scalp, elbows, axillae, cheek sockets, vulva, and abdominal and buttock grooves are not invaded, or there is only mild scaling. Usually there is no conscious symptom. In winter, due to the decrease of sweat gland and sebaceous gland secretion, the skin is dry and may be itchy and uncomfortable, or painful if chapped. Sexually linked ichthyosis is rare. The causative gene is on the X chromosome, and the female is the carrier, usually without onset or sometimes only with thin scales on the forearms and lower legs. Patients are male and develop after birth or in infancy. The lesions are slightly different from the common type, with large and prominent scales, yellowish-brown or blackish-brown, dry and rough skin, often all over the body, including the axillae, the fossa and the elbow fossa, and the abdomen is more severe than the back. If the face is involved, it is limited to the front of the ear and the side of the face. Follicular keratinization does not usually occur. The palmoplantar skin is mostly normal, and the lesions do not decrease with age, but sometimes increase. The disease may have small cloudy spots on the posterior corneal wall and posterior elastic laminae, which do not affect vision. Laminar ichthyosis is autosomal recessive and is much rarer. After birth, the entire body is tightly wrapped in an extensive lamellar membrane, causing ectropion of the eyelids and lips called lamellar infants. After a few weeks, the membrane is shed and the skin is extensively and chronically flushed with grayish or grayish-brown polygonal or rhombic scales, with a central fixation and free edges. It tends to occur symmetrically all over the body, and is more obvious on the flexural side of the limb, elbow fossa, national fossa, axilla and vulva. The palmoplantar hyperkeratosis, nail and hair overgrowth. The course of the disease is delayed and can last for a lifetime, and the erythroderma can be reduced in adulthood, but the scales are still present. Ichthyosis is a hereditary skin disease, and genetics is an important factor in causing the disease. In addition, abnormal lipid metabolism, low VitA level and microcirculatory disorders are also thought to be involved in the development of ichthyosis. There is no specific treatment available. The disease does not affect the life expectancy of people, but only brings inconvenience to life. The goal of treatment is to increase the hydration of the stratum corneum, promote normal keratinization, moisturize the skin and relieve symptoms. Topical emollients can be used to reduce the clinical manifestations of ichthyosis. Commonly used topical drugs include 10% cod liver oil ointment, 10%-20% liquid paraffin or pure product, 10%-30% urea cream or ointment, 3%-5% salicylic acid ointment, 0.03%-0.1% vitamin A acid ointment or lactic acid preparation, etc. If these drugs are applied externally after a warm bath, the effect is better when wrapped in cling film for several hours to more than ten hours. Oral or intramuscular injection of vitamin A (200,000-300,000 units/day), continuous treatment for several months, also has a certain effect. However, it should be noted that the large-scale long-term application of certain topical preparations such as salicylic acid preparations, or long-term application of large doses of vitamin A have some toxicity.