This was actually a subject I was curious about myself: almost a quarter of all pregnant women experience worsening allergies during pregnancy, sometimes even if they never had any allergies before pregnancy. Women who had mild asthma beforehand are at a higher risk for severe asthma attacks, and runny noses, sniffles and sneezing get worse as well.

So I did a little digging, and here’s what I discovered.

Higher Sex Hormones = Natural Steroids

On one hand, during pregnancy hormones spike, of course. All of the sex hormones are steroid hormones, meaning they cause immune system suppression. For this reason, during pregnancy, many autoimmune conditions (but not all) tend to improve… so you’d think allergies would too. After all, the fastest way to quench an allergic response is with steroids.

Pregnancy = the Ultimate Immune System Hijacking

On the other hand, the very fact that pregnancy ever happens at all is pretty amazing, when you think of how many things have to go perfectly in order for it to happen. The whole point of your immune system is to protect against foreign invaders—and yet here’s an embryo that is decidedly not Mom — breaking through the zona pellucida (the membrane surrounding it prior to implantation—so basically it hatches), secreting its own cytokines, invading the uterine tissue, and implanting into the endometrial wall—after which the embryo hijacks Mom’s endometrium, diverts its blood supply for the embryo’s own purposes, and then proceeds to turn the endometrium into its very own hormone producing factory.

It sounds pretty nefarious, and yet Mom’s immune system turns a blind eye. The embryo accomplishes this feat by producing a unique molecule called HLA-G, which essentially identifies itself to the immune system as “Don’t shoot, I’m a friend!”

And just in case the immune system is inclined to shoot anyway, the embryo produces a ligand (like a key) called the Fas ligand that, when it fits into the corresponding Fas receptor carried by other immune cells, essentially commands the other guy to self-destruct.

Less Sledgehammer, More Paranoia

Under ordinary circumstances, the job of your immune system is to react only to insoluble antigens, or invaders (viruses, pathogens, cancers, etc)—and to let soluble antigens (allergens) and self antigens (cells that are part of your body) slip by without comment. Your immune system accomplishes this with a one-two punch: first, it will attack in a quick-and-dirty fashion (called “cellular immunity,” in which the cells themselves release an arsenal of inflammation to kill the bad guy). Only then does it create antibodies against the invader (“humoral immunity”) so that it can direct its forces only at the invader with a little more finesse, thus minimizing collateral damage.

But the specific part of the immune system that has to get dampened during pregnancy is the first part, the “cellular immunity.” Mom’s body will thus shift the ratio of the two immune responses in favor of humoral immunity… which means more antibody production. To everything. (But not the fetus, because it’s sneaky like that.)

What To Do About Allergies in Pregnancy

Avoid triggers that cause the release of histamine. Allergies are cumulative (meaning your body reacts similarly to environmental allergens, chemicals, and foods to which you are sensitive); so definitely minimize your exposure to chemicals as MUCH as possible (not just because of allergies, but also because many solvents have been shown to cross the placenta—babies are now being born pre-polluted!).

Consider finger prick or blood food allergy testing. Even if you never had allergies before, you might now — or you might have had them already but they were below the threshold of your body’s ability to deal with them, and now they’re not. In any case, because allergies are cumulative, if you can remove these and limit your chemical and dust exposures, then it’s possible your immune system will be able to handle the rest. But at least you’ll be significantly less reactive.

Get a HEPA filter. This will take care of whatever you can’t avoid chemically, and should also greatly decrease dust particles too — highly allergenic. (Here’s a link for the one I have.)

Take probiotics. It’s about the best thing you can do to keep your gut lining healthy. Here’s my favorite one:

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