Question: why is it that everybody has reactions to different things such as penicillin which i am.

Ailsa Powell answered on 21 Jun 2011:

So a reaction to penicillin is a allergic reaction. This means that your immune system has mistakenly decided that the penicillin is a threat and when it detects penicillin is generates an immune response, which can be very severe.

The first time you took penicillin you would have been fine, but your immune system decided it was bad and produced antigens against it. These antigens allow your body to remember the things that it didn’t like. This is very useful when antigens are produced against bacteria and viruses as your body is ready to fight the cold or infection immediately. The antigens are not so useful when they have been produced against something not harmful like penicillin and they will start the allergic reaction once they detect penicillin in your body.

Why some people get this reaction and others don’t is down to differences in our immune systems. Some people have immune systems that are more primed to generate allergic reactions. Often a there is a genetic link, one or both of your parents may have a tendency to have allergic reactions. If your immune system is more likely to generate allergic responses you unfortunately can’t really predict what it will generate immune responses to, which is why people have a whole range of different allergies.

Now the reaction you have to penicillin is different to side effects from taking medicines. These are because the medicines are slightly toxic to the person taking it and they can feel a bit ill from the medicine. Usually doctors decide that the benefits from taking the medicine will outweigh the possibility of side effects. Again different people can suffer side effects in different ways, and it will be because of the differences in people.

Hope that answers your question 🙂