Good question! There are many different types of allergies and many different reasons why one person might have them and their best friend doesn't. For example, some people are allergic to dogs, some to different types of food and some to pollen that comes from flowers in the springtime- called "hay fever". NO matter what you are allergic to, the result is the same. Allergies occur when your immune system is overly sensitive to certain molecules (dog skin, pollen, peanut oil). Normally our immune systems job is to protect us from things that are harmful to our body like viruses that cause you to get the flu and bacteria that make you get a cold. When you have an allergy your immune system thinks harmless things like peanuts could hurt you like a virus. so to protect you immune cells try to get rid of the harmful substance (called an antigen) by causing you to swell up, turn red itch, sneeze and cough. Your body is just trying to protect you, but from the wrong things...it is TOO SENSITIVE!

SO, why do some people have allergies and others do not?? One reason has to do with your parents. Sometimes if you parents have an allergy you will also get that allergy, this is called inheritance. Another reason is because the person that is allergic was around the thing they are allergic to when they were a baby or really young and the other person was not. If your favorite sandwich was Peanut Butter and Jelly when you were a baby then you are more likely to be allergic to it when you get older. This might sound a little confusing, and it can be but, the only thing you have to remember is that you get allergies when your body's immune system recognizes normal things that dont hurt you as things that can hurt you. I guess you could say the immune system is broken although most people can handle a little sneeze and cough every once in a while.

I hope this answers your question.

This a great question and one that many scientists would really like to be able to answer in detail. For example, not only might this knowledge help doctors treat an allergy, but also predict who might develop an allergy and importantly, prevent it.

A key part of the answer to your question is in understanding what an "allergy" really is. Let's take an example of someone who is allergic to pine pollen and dog hair.You probably know what the symptoms of the allergy are - watery eyes, maybe a stuffy nose and scratchy throat. This is due to an immune reaction - that person's immune cells recognize the pollen and dog hair as something that needs to be "attacked" and so they produce specific chemicals that lead to the symptoms. But why is that person's immune system doing this when yours is not? This is the big question, the one you are asking!

Until fairly recently, most scientists and physicians thought that there was a strong genetic aspect to allergies - in other words, if your parents have allergies, you have a good chance of developing allergies. However, exactly "why" is still a mystery. Genetics could explain a lot, because your immune cells operate on a recognition system and each person has a specific "identity" that the immune cells are constantly surveying. The "sensors" used by the cells are specific proteins, encoded by genes. But now, it seems pretty clear genetics cannot explain it all - there seem to be environmental and lifestyle factors. We do not know much about how the immune system is set up during the development of a baby and a young child - some scientists think that decreased exposure to potential allergens during infancy and childhood results in allergic responses; in other words, being too clean is a bad thing when young (this is called the "hygiene hypothesis" and is still much debated). Food allergies seem to be on the rise and this is a real mystery as to why. Some scientists are studying if food allergies operate under the same general set of rules as other kinds of allergies, like hay fever.

Thats a great question! Allergies are caused by a problem with a persons immune system is hyper.(Your immune system is what causes you to have a fever or get a snotty nose when you have a cold, its your bodys natural defense system). Things that cause allergies are called allergens, and can be both natural, like flower pollen, and man-made, like certain medications. When a person who is allergic comes in contact with an allergen, their immune system goes into overdrive against it for no good reason. Thats why your eyes and nose get runny, and in some serious cases breathing can become difficult.

No one knows exactly why some people get allergies and others dont. It is a mix of a persons heritage and how often they contact potential allergens. Some people become allergic to things over time. For example, I am now allergic to walnuts and my mouth swells up when I eat them, but as a kid, I loved walnuts! Sometimes, allergies seem to be caused by too much exposure... maybe I ate too many walnuts when I was younger! Some scientists also believe that people today have more allergies than in the past. Scientists think this because as kids, our immune systems dont get used to be exposed to plants and like people did when most people farmed.

Luckily, most allergies are not too serious and can be managed by avoiding the cause of the allergy as much as possible!

Different people have different chemical receptors in their immune cells that react to specific stimuli in the environment, creating an allergic reaction.