Molluscum contagiosum is called vitamin D deficiency rickets, and the causes are insufficient sunlight exposure, insufficient vitamin D intake, low calcium content or improper calcium-phosphorus ratio. 1. Insufficient sunlight exposure: Vitamin D is produced by the skin through sunlight, and insufficient sunlight in winter will lead to insufficient vitamin D synthesis. For infants and children, sunbathing is an important way to make the body synthesize vitamin D3. 2. Insufficient intake of vitamin D: Animal food is the main source of natural vitamin D, such as herring sardines and other marine fish, animal liver, cod liver oil, eggs, beef, butter and vegetable oil. When the vitamin D intake from natural food is not enough to meet the growth and development needs of infants and young children, they should get more sunshine and supplement cod liver oil. 3. Low calcium content or improper ratio of calcium and phosphorus: Insufficient calcium in food and improper ratio of calcium and phosphorus can affect the absorption of calcium and phosphorus. Patients with achondroplasia need to be treated actively with medication under the guidance of a doctor.