Allergies are caused by what?

I have oft heard that if you expose a child to things such as cats or dogs while young, they will not develop allergies to them when older. Well I have had cats almost my whole life & just found out I am allergic to cats! I have also eaten beef ...

I have a 9 month old YorkiePoo puppy. I've had him since he was about 9 weeks old and just within the last few weeks I've noticed that I get itchy and break out in hives after brushing him. I'm having very minor itching throughout the day intermittently...

I think I have hives because my skin is itchy and tingly in random areas of my body. So I'm trying to find out what caused it... abalone: I ate abalone for the first time a couple of days ago, but I found out that if you are allergic to it, you're allergic...

My nose just won't stop bleeding, and it's because of my allergies, but the blood isn't really coming from inside of my nose...more like way down in my sinus cavity. It doesn't drain out, it just pools there, causes pressure, and blocks my breathing...

My cat whom I've had since she was a kitten has developed some kind of allergy within the last 2 years. I've moved her around the country to many new /different homes and changed her diet over the years as well. She never seemed to have any problems...

Last week I started getting what seemed to be a soar throat that would get worse whenever I put the air-conditioner on fan instead of regular cool mode. (I never made the place too cool..if anything I try to save energy by leaving it on the warm side...

Do you know what would cause me to just forget things. My son asked me to look up some info. on the internet yesterday & this was about 7 a.m but I didn't remember it til about 10 P.M. I really was looking for ways to help him out so I don't know...

My family and I just got back from camping at the Colorado river where I was in 100 degree heat and sunlight for the past two days. This morning I woke up and I have small red hives all over my body, especially on my arms. I also have slight nausea....

Some days it will be plugged, some days it won't sometimes it won't be so bad, and other times it will be really bad. What do I do to unplug them?