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Ever Wonder About Antihistamines?

This spring, my eyes have been itchy and my nose has been runny, sneezy and all the other dwarfs. The pollen report said levels have been high for alder, cedar and other trees, so I will blame them and their pollen, since I have not heard the Lorax speak for them lately.

If I know I’m going to stay home, I’ll usually just rinse my sinuses with a neti pot and that seems to help. But if I have to go out, I take an antihistamine. It used to be that they would conk me out, but new ones don’t seem to do that. I wondered why.

The histamine that antihistamines are anti to is a multi-purpose molecule used in the immune response, as well as other processes. When grains of pollen land in my nose or other sensitive places, receptors in my cell walls lead to an overreaction, as though that thing was harmful—even though it isn't, really. In these tissues (nasal tissues, not to be confused with the ones I blow my nose into),  mast cells can dish out a superstore of chemicals in response to various stimuli. In this case, they release histamines into their surroundings. A basophil, a kind of white blood cell, also releases histamines.

Cells react to histamines differently, depending on what kind of histamine receptors they have. So far, four kinds of histamine receptors have been found, unimaginatively called H1, H2, H3 and H4. The H1 type triggers the classic hay fever reactions by causing cells to become leakier, so noses run and things swell up. It is these H1 receptors that antihistamines target.

Antihistamines (which I might have called her-stamines) don’t prevent the release of histamines, but instead, interfere with what the histamine does. Swiss-born, Italian pharmacologist,  Daniel Bovet, won the Nobel Prize in 1957 for his discoveries about antihistamines, among other things. Antihistamines work by looking enough like a histamine to fool H1 receptors and yet not so similar that they cause a reaction. Different companies have their own version of antihistamines that involve different chemicals. They each act a little differently, so you have to try them out to see which one works best for you.

Another thing that histamines do is keep you awake. The first-generation antihistamines made people feel sleepy because they also conked out histamine receptors in the brain. The newer, second-generation antihistamines (which I might have called uncle-histamines) do not seem to have this effect. Although they can all cross the  blood-brain barrier, which limits the sorts of molecules that can enter the brain, they are less lipid soluble and do not seem to impair the histamine receptors as much as the earlier kinds. Still, don't assume that you will be okay to drive even after taking a second-generation pill.

Normally, I'd ask for your comments, but this time, I don't really want to hear about your runny nose. Take care.

Learn more about runny noses, itchy throats and other less-polite aspects of the human body by visiting our BodyWorks Gallery!