That makes sense.  Years ago I was taking benadryl as needed when my hearburn started to get bad.  Then the doctor put me on PPI's and my health went down hill fast.  I swear I had every test known to man done to me except the one for stomach acid production.  Now looking back it seems like it should have been pretty obvious. 

Right-- older first-gen or sedating antihistamines would-- so diphenhydramine (benadryl) will shut down some acid production via proton-pump inhibition (well, actually H2 receptors), but that is because it hits BOTH types of receptors.

This is also why those older drugs are sedating; they hit H1 receptors (systemic antihistamine impact) and also H2's-- gut and CNS.

The antihistamines we take for allergies are H1 blockers. The medicines we take for heartburn, etc. (Zantac, Pepcid, etc.) are H2 blockers. I'm not sure H1 blockers have much effect on stomach acid production.

I was just reading about how the body uses histamine to signal the creation of stomach acid.  I hope I'm wrong, but here's how I see it.  We take antihistamine to control allergy symptoms.  Which it does, but it also reduces stomach acid which can cause new allergies and hypochlorhydria. 

That is consistent with the body of current knowledge. Sensitizing is better understood than reversing it. Controlling symptoms is also understood, but as CM noted the off switch for sensitization is yet to come. Until that gets plugged into the equation there's no off button discovered even though the on button(s) is more or less understood.

I'm not expert, I'm just a guy going through these issues that's done quite a bit of research.  It's my understanding that if reduced stomach acid causes an allergy then supplimenting acid has a chance of fixing the allergy.  Clearly not all allergies are caused by stomach acid issues.  Since the 2 have common ties just I can't believe that it's not common practice to test for Hypochlorhydria if you are diagnosed with allergies!  It seems like common sense to me. Plus my stomach acid issues would probably have been discovered 30 years and countless medical bills ago. It's been a pretty serious problem for me for the last 7 years, but to a lesser extent I think I've had it my whole life. 

I developed shellfish and sesame allergies while on a proton pump inhibitor. There is research that suggests it could play a role in developing FAs.  It's not "out there" research.  My Duke allergist thought the connection was plausible and also thought it might be possible for my gut to heal. At the time it looked like I had outgrown crab.

The possible connection makes me wonder if teh symptoms I get for shellfish--almost always delayed 2 hours and GI symptoms--really do have something to do something in my gut that's not right. 

I'm not Asian, but really wish that the H2 blockers would turn off the alcohol flush for me.

I think it's one of those things where histamines can have an effect on a wide variety of organs/systems. It's probably more a symptom rather than a root mechanism. I'm sort of tempted to ask OP if he or she is East Asian because there's a funky thing with alcohol, histamines and the 'Asian flush' so many of us get. H2 blockers like Pepcid AC seem to turn it off but that's a symptom controller, nothing more.

Um... totally not implying anything about OP and booze that was bad wording on my part. I meant more the acid blocking and histamine blocking is interchangeable in some instances.

Unfortunately, at this point the "off" mechanism is unknown re: sensitization.

So does this imply that by correcting the stomach acid issue something like allergies could reverse?

related:

http://www.ncbi.nlm.nih.gov/pubmed/18539189
https://etd.library.emory.edu/view/record/pid/emory:bprr1

The home test from http://www.prohealth.com/library/showarticle.cfm?libid=13388

[Ed Note: As with all health issues you should discuss stomach acidity, testing, and management with your professional healthcare team. But a simple preliminary test of stomach acidity is to drink a small amount of baking soda in water first thing in the morning. If you have not belched within a few minutes, you may not be producing enough stomach acid, since hydrochloric acid reacts with baking soda to produce carbon dioxide gas. See "Stomach Acid Assessment" by Dr. Joseph A. Debe.]

I recently started taking a stomach acid supplement for reasons not related to this forum.   After a little research I came to find that Hypochlorhydria or low stomach acid is linked to both allergies and asthma.  I was diagnosed with allergies and asthma 30 years ago.  I've seen 4 different allergists along with a number of other doctors and none of them ever even considered checking for this issue.