Hypertension is a disease caused by a combination of multiple factors. It develops when the cause of primary hypertension is not known; while secondary hypertension develops from a variety of diseases or its complications are hypertensive. Today we will learn what diseases can cause hypertension. 1, renal parenchymal lesions: common renal parenchymal diseases include acute and chronic glomerulonephritis, polycystic kidney, chronic pyelonephritis, obstructive nephropathy, gouty nephropathy, diabetic nephropathy, lupus nephritis, scleroderma, etc. Hypertension caused by renal parenchymal lesions is often very difficult to treat and is the main cause of hypertensive emergencies in young adults. 2, endocrine hypertension: including primary aldosteronism (proaldosteronism), pheochromocytoma, Cushing’s syndrome, and hyperthyroidism. Due to its corresponding hormones such as aldosterone, catecholamines, cortisol and other excessive secretion, resulting in hemodynamic changes in the body to increase blood pressure, resulting in hypertension. 3, renal artery stenosis: narrowing of the main trunk or branches of the renal artery, resulting in ischemia of the affected kidney. Renal ischemia, the kidney self-protection mechanism is activated, and the activity of renin-angiotensin system is increased, prompting the blood pressure to rise to meet the supply of blood to the kidney. Therefore, hypertension is formed. 4, aortic constriction: aortic stenosis leads to redistribution of blood flow and renal tissue ischemia, triggering water and sodium retention and renin-angiotensin system activation. Both are also protective responses to ischemia in the kidneys as well as in all organs of the body, and the blood pressure is increased to ensure blood supply to the kidneys as well as to all organs of the body. 5, obstructive sleep apnea hypoventilation syndrome: sleep apnea hypoventilation syndrome is due to the collapse of the pharyngeal muscles blocking the airway during sleep, repeated apnea or significantly reduced oral and nasal air flow, clinically mainly now as sleep snoring, frequent apnea phenomenon, is one of the important causes of intractable hypertension. Through the above summary we can find that hypertension is not an individual disease, it is a complex, multi-factorial formation of the disease. And most of the elevated blood pressure caused by the above diseases is a protective mechanism of the body. So we must review and understand how it causes hypertension. Blindly lowering blood pressure may sometimes cause more damage. For example, in patients with renal artery stenosis, blood pressure rises and renal blood flow is maintained, which can slow down the kidney deterioration caused by kidney ischemia, once strong antihypertensive drugs are used, blood pressure drops, which reduces the blood supply to the kidney and accelerates the kidney deterioration. Patients must realize the truth that whatever is abnormal is bound to have a cause. Blind treatment without thorough investigation of the cause is undesirable and potentially dangerous. Clinically refractory hypertension is often an alarm for the body. It is something wrong with a part of our body. Therefore, if you have high blood pressure, you must go to the hospital to find out the cause before treatment. Otherwise, it is like “the blind man feeling the elephant”, only looking at the part, not the whole.