What good are allergies?
My daughter called me the other day. Our two-year-old grandson had developed a skin rash that was spreading rapidly. The rash involved whitish areas surrounded by rings of red. I asked if our grandson had just eaten or taken medications. It turned out that he had just taken medications, a commercial cold medicine and a pain reliever.
I advised my daughter to watch our grandson for signs of breathing difficulty and if he did to get him to the doctor quickly. This is because, he was apparently having a type 1 hypersensitivity reaction which can involve acute breathing difficulties. I also advised her to give him something containing an anti-histamine such as Benadryl.
A type I hypersensitivity reaction is what we normally think of when someone says they suffer from allergies or an allergic reaction. As many of you already know, these reactions can occur to a wide range of substances in our environment, including pollens, animal dander, house dust mites, molds, foods, insect venoms, medicines (including some antibiotics and even pain relievers), rap music (just kidding) etc. Reactions can occur by direct contact with skin, breathing, and ingestion. Regardless of the agent and the route of exposure, the type I hypersensitivity reactions can usually be easily diagnosed based on their timing. These reactions almost always occur within minutes of exposure to the offending substance. And they peak within minutes or hours after exposure. This is in direct contrast to poison ivy and sumac reactions, for example, that involve type IV hypersensitivity.
Type IV reactions almost always take hours to occur and don’t peak until one to two days following exposure. They also do not usually result in shortness of breath normally. Type I and type IV reactions also respond to different types of treatment. Type I hypersensitivity reactions involve histamine so that anti-histamines (such as the active ingredient in Benadryl) that block the action of histamine are very effective in decreasing the severity of these reactions. In contrast, skin rashes due to Type IV reactions such as occurs to poison ivy are best treated by topical creams containing hydrocortisone (such as Cortaid). By the way, some people don’t react to poison ivy. My son can literally rub this stuff on his arm and not respond. Don’t ask me how he figured this out - and don’t try this yourself!
The reason that type I hypersensitivity reactions sometimes cause acute breathing difficulties is because histamine causes contraction of a type of muscle found in the bronchioles of the lungs (called smooth muscle). Contraction of this muscle can cause these airways to close off. If you ever think someone is having this kind of acute breathing reaction, get them qualified medical help, fast.
So why does our immune system respond to pollens and otherwise harmless substances in such a way that can sometimes harm us? Our immune systems do not exist to make us miserable. They are designed to protect us from infectious agents and cancer. The molecules and cells involved in type I hypersensitivity reactions are very effective in fighting parasitic worm infections (such as tapeworm) which are not much of a problem in developed countries but are a major cause of disease in many developing nations. Why these responses are mistakenly stimulated by things such as pollens etc is a mystery which Immunologists are still trying to answer.
Just to finish the story, my daughter called the nurse and got the same advice she had received from me. The nurse thought it was probably the cold medicine that had caused the allergic reaction but we still don’t know for sure.
Below is a pciture of my grandson’s Type I hypersensitivity rash (hives):
