The causes of high blood pressure are complex, and high blood pressure in a 20-year-old child is likely to be caused by primary hypertension or secondary hypertension, as well as conditions such as incorrect blood pressure measurements. There are many causes of high blood pressure. At present, high blood pressure can be divided into primary hypertension and secondary hypertension. 1. Primary hypertension: Hypertension is hereditary, and children of hypertensive patients are significantly more likely to develop hypertension. People who are seriously overweight are easy to get primary hypertension. In addition, excessive intake of sodium and drinking a lot of alcohol may directly cause primary hypertension. 2. Secondary hypertension: secondary hypertension is usually caused by underlying diseases, such as chronic nephritis, hyperthyroidism, etc. It is necessary to find out the cause of the disease as soon as possible, and then treat the primary disease. 3. In addition to primary hypertension, secondary hypertension, there are also situations such as blood pressure measurement errors, such as measuring blood pressure before not resting quietly for more than 10 minutes, there is no drinking coffee, strong tea, or taking drugs or food that cause blood pressure rise, cuff whether elasticity and tightness of the appropriate, and white coat hypertension, or emotional tension, stay up all night caused by sympathetic excitation caused by elevated blood pressure. 20-year-old child high blood pressure, need to go to the hospital to identify the cause, and then targeted treatment.