Here we must talk about the principle of allergy. You know that human immunity means that when germs, viruses or other chemicals (these are called antigens) invade the human body, the human immune system will play a role. Immunity can be divided into specific immunity and nonspecific immunity. Nonspecific immunity means that no matter what harmful substances enter the human environment, phagocytes and bactericidal substances in the environment will "digest" and kill those harmful substances; Specific immunity refers to some stubborn harmful substances, such as phagocytes and bactericidal substances, which cannot be eliminated, so specific immunity is needed, typically humoral immunity. This process is very complicated. Simply put, the antigen stimulates B lymphocytes to proliferate and differentiate into plasma cells, memory B cells, and plasma cells secrete antibodies corresponding to the antigen through various processes. The next time the same antigen invades again, it will be recognized by memory cells, rapidly proliferate and differentiate into plasma cells, and secrete more antibodies. Antibodies will combine with antigens to form cell clusters or precipitates, which will eventually be digested by phagocytes and the pathogens will be eliminated. Of course, more stubborn viruses will invade tissues and cells. At this time, the human body will start cellular immunity, which is more complicated, so I won't say it. You can search Baidu for "three lines of defense against human immunity", which may be introduced in detail.
Having said that, here comes the protagonist. "Allergy" is also an immune response, commonly known as "autoimmune disease", including systemic lupus erythematosus and rheumatoid arthritis. That is, the immune system will recognize some harmless substances that enter the body as harmful substances, thus starting humoral immunity and producing antibodies to combine with these substances. This kind of antibody is different from ordinary antibodies, and it won't work the first time. In the image, they will hide in corners such as blood vessels. When the substance enters the internal environment for the second time, it seems to be "awakened" and dissociated into the internal environment (plasma, interstitial fluid, etc. ) and combine with those substances. At this time, a substance called histamine will be released, which will change the permeability of cell membrane. For example, your capillary wall will ooze plasma protein under the action of histamine, causing tissue edema, which is the papule on your body, which is what we usually call skin allergy. Antibodies do not act on this part.
Well, that's why you are allergic. To sum up, some ingredients of hairy crabs are unacceptable to your body, and your immune system will attack and cause allergies. The most direct way to treat allergies is to take anti-allergic drugs. The principle is to temporarily reduce human immunity, thus ignoring those reactive substances, which is not good for human body. There are some special circumstances that will lead to changes in the expression of certain genes in the human body. Maybe after many years, you are no longer allergic to substances that you were allergic to. This rarely happens.
In short, the way to prevent allergies is to stay away from allergens, know that you can't eat them, and don't be greedy for a while to damage your health.
The full text is written by hand, which is one-sided macroscopically, but the one-sided way is detailed enough to almost condense the content of the biology textbook for you to understand. I didn't copy a word.
Typing is not easy, but I hope to adopt it (how to adopt it can be Baidu)
thank you