After the weather gets colder, the number of children suffering from allergic purpura increases significantly, many parents do not understand the disease, and they are very anxious to see the bleeding spots appearing on their children’s lower extremities, therefore, the consultation about this disease also increases significantly during this period of time, and now parents and friends are more eager to know, if in the outpatient clinic or ward, the doctors hardly have time to explain clearly for you. I take the opportunity to talk about a little knowledge of the disease here, and I hope it will be helpful to you. Allergic purpura is discovered by parents as an accidental discovery of many bleeding spots on the child’s lower extremities, usually below the buttocks, especially the rash on the calves and ankles. In some cases, the bleeding spots are only discovered when the child remembers to lift the child’s clothes when he or she develops pain in the lower extremities and walks with a limp. Some children have obvious swelling and pain in the knees, ankles or calves; some also have abdominal pain (mostly around the umbilicus and upper abdomen, which can be vague or severe), and during abdominal pain, the child is usually unable to eat or drink, or even vomits. The four most common symptoms of allergic purpura can be seen above: rash, joint or gastrocnemius pain, abdominal pain and kidney damage. These symptoms of allergic purpura are caused by the inflammation of necrosis of some small and medium-sized blood vessels in the body, which means that some small blood vessels in the affected area are inflamed and necrotic. If the blood vessels in the skin are involved, there will be a rash of varying sizes with bleeding skin that does not fade when pressed. Some of these rashes are as small as a pinpoint, others are as high as an adzuki bean, and others may fuse into a large patch; they are usually bright red when they first appear, then darken and fade after a day or two. If the synovial vessels of the joints become diseased or the blood vessels in the muscles are invaded, then swelling and pain in the joints can occur, so some children begin to have difficulty walking, the surface of the foot or knee joint is obviously swollen, and the gastrocnemius muscle (calf stomach) cannot be touched; if this inflammatory reaction occurs in the mesenteric or intestinal wall blood vessels, then abdominal pain will occur, and it will also cause a temporary decrease in gastrointestinal function, and appetite will be affected. Appetite will be affected. If the larger blood vessels of the intestinal wall are involved, there may be bleeding in the gastrointestinal tract, and if the involved blood vessels are large, the amount of bleeding will be large. The glomerulus in the human kidney itself is surrounded by small and medium-sized blood vessels, therefore, the kidney is also easily affected, which will then manifest as microscopically detectable hematuria, naked-eye visible hematuria, proteinuria, etc. In severe cases, swelling, oliguria and reduced kidney function can occur. In fact, as long as there are blood vessels, all may be involved and show different symptoms, but the above four symptoms are more common and most children show symptoms, if only the rash, it is called simple purpura; if in addition to the rash also combined with abdominal or joint symptoms, it is called mixed purpura; if the kidneys are involved, it is called purpura nephritis. In fact, the most common and intuitive symptom for parents is the rash, which is also the least important symptom, because the rash will gradually fade away with time, and there will be no pigmentation or scars, and no special treatment is needed for the rash, and in fact there is no good way to have a definite effect on the rash. Whether the rash appears in batches or not is only indicative of whether the disease is still active. Swollen joints or muscles are usually noticeable at the onset of the disease and will improve to disappear within a week or so, and most of the swollen joints will not leave any deformities or sequelae, so there is no need to pay much attention to them. Parents should be most concerned about the symptoms of abdominal pain, and the most important thing to observe is the child’s stool pattern during the abdominal pain, which is the most important because if there is a large amount of bleeding, the loss of a large amount of blood from the intestines can be life-threatening, so I often say that this is the most dangerous symptom. The most troublesome of the four symptoms has to be the manifestation of kidney damage, because the first three symptoms will generally disappear or get better soon as long as they are handled properly, once the symptoms of kidney involvement appear, at least one to three years of attention and follow-up are needed. Having said that, friends must be concerned about how this disease is actually obtained? Is it caused by any allergy? Do you need to check for allergens? In fact, the exact pathogenesis of the disease has not yet been fully studied in medicine. It is difficult to use one theory or doctrine to explain all the phenomena, as the triggers of the disease vary from patient to patient. What is known and widely accepted is that different triggers (initiating factors) cause an abnormal response of the body’s immune system and result in inflammation of the blood vessels causing necrosis. Although the name of the disease is allergic purpura, not all patients are allergic to it, the real cause of the disease is caused by various substances (such as food, drugs, pollen, insects and mites, chemicals) in less than one third of clinical cases, and the most common clinical occurrence is after bacterial or viral infections, therefore, strictly speaking, it is called “allergic” purpura. The allergic” purpura is inaccurate and has caused a lot of misunderstandings among parents and friends, and sometimes the allergen test results are even more confusing. The immune system is like a country’s army, police, militia and security system, when there are foreign troublemakers invasion, they play a protective role; but occasionally, they overreact or malfunction, will fight with each other or hit the good people of their own family. This is somewhat like allergic purpura, regardless of what factors initially triggered it (infection or allergy), but the result is that while clearing these factors, its own blood vessels are unlucky and follow the attack with necrotic inflammation, thus triggering a series of symptoms. The purpose of our treatment is to find ways to disarm these red-eyed defense systems (such as the use of immunosuppressive drugs such as hormones if necessary in the early stages), so that they can calm down and return to a normal state; at the same time, in order to prevent these defense systems in an agitated state from overreacting, avoid some factors to provoke the system again in the early stages of the disease or for a period of time as possible. For example, controlling possible infections as soon as possible, avoiding allergy-prone foods or medications, avoiding exposure to potentially harmful chemicals: paint, gasoline, benzene, etc., avoiding vaccinations during this period, staying away from pollen or mites for a while, getting rid of internal parasites, etc. Therefore, when this disease occurs, it is important to actively look for possible causes in order to anticipate a relapse, but for the disease that has already occurred it is important to calm the immune system with time or medication as soon as possible; this is why the clinic uses medication along with some dietary and living precautions. Finally, it is reminded that about more than one third of children with allergic purpura will have clinical kidney involvement and the vast majority of them occur within 6 months of the onset of the disease. Therefore, within 6 months of onset, special attention should be paid to frequent observation and testing of the child’s urine for early detection of kidney damage to help the physician provide timely and targeted treatment. Overall, with timely detection and proper treatment, the prognosis of most purpura nephritis is good, and quite a few patients with kidney damage have their indicators return to normal within a year, but follow-up should preferably be adhered to for 3~5 years.