Dear Hailey,
Under my lab coat, I have a splendid fur coat. That can be a problem when I work with someone who’s allergic to cats.
I asked my friend Ed Johnson about it. He teaches classes about the human body at Washington State University.
He told me that allergies happen when your immune system overreacts to a normal thing it perceives as a threat to your body. That thing can be pollen, dust, food, medicine, insect venom or something else. It can be bits of fur and shed skin called cat dander.
“The immune system evolved to protect the body,” Johnson said. “For allergies, it does that with mast cells, which are found throughout your body.”
Mast cells are a type of white blood cell. They’re made deep inside your bones. They hang out in your tissues. They make and store chemicals the body uses during allergic reactions.
Let’s say you’re allergic to cat dander and breathe some in while admiring my luxurious pelt. It goes up your nose and into your body. Your immune system immediately recognizes the dander shouldn’t be there. It starts cranking out proteins called antibodies—especially immunoglobulin E.
That protein is specific to whatever is causing the allergy—like cat dander. It sticks to the outside of the mast cells.
If another bit of dander comes by, the proteins stuck to the mast cell will grab the dander. That makes the mast cell dump out a chemical called histamine.
Histamine makes lots of changes in your body. It adjusts your blood vessels and tissues so more immune cells can rush to the area. It makes a bunch of mucus. It tells the muscles in your airways, stomach and intestines to move so they can push out the dander.
That histamine dump is why you get allergy symptoms.
“It causes hives and swelling that’s due to excess fluid being in the tissues,” Johnson said. “It causes an increase in mucus and stuff in the airways. It’s why you get sneezes and puffy eyes and all those symptoms. They’re just a byproduct of the histamine released by the cells trying to protect your body.”
Sometimes people have a very serious allergic reaction called anaphylaxis. Their airways swell so much that it’s difficult to breathe. They have dangerous changes in their blood vessels. That’s an emergency that requires immediate medical help.
Scientists know how an allergic reaction works. But they aren’t sure why some people get an allergic reaction and other people don’t. They’re not sure why some people have serious allergies to normal stuff that can’t really hurt them—like cat dander. Or, in the case of cats, why some are allergic to dander from dogs or humans.
That hista-means it’s a science question ready to be studied by a curious person like you.
Sincerely,
Dr. Universe