Allergy Changes During Pregnancy and Their Clinical Management

Pregnancy does not follow one rule for allergies. It can make existing allergies worse, better, or leave them unchanged, and it can trigger brand-new allergic reactions in women who never had one before. Figuring out which pattern is happening in a given pregnancy starts with understanding what pregnancy actually does to the immune system.

How Pregnancy Reshapes the Immune System

Pregnancy pushes the immune system toward Th2 polarization. That is the same branch of immune activity that drives allergic responses, so the baseline immune environment of pregnancy already leans in a pro-allergic direction before any allergen is even in the picture.

Hormones add another layer. Elevated estrogen stimulates histamine production, and increased blood flow to the mucous membranes causes nasal tissue to swell. That swelling can look and feel exactly like allergic congestion, even when no allergen is involved.

When you put those two mechanisms together, things get messy fast. A woman's existing allergies might worsen. They might ease up. They might stay exactly the same. Some women develop allergic symptoms for the first time during pregnancy, with no prior history at all, and none of these outcomes can be predicted reliably in advance for any individual patient.

This is where diagnosis starts to matter as much as treatment. Pregnancy rhinitis is a separate condition, and it causes nasal congestion from hormonal and vascular changes, with no allergen involved. If you treat pregnancy rhinitis as allergic rhinitis, you expose the patient to medication she doesn't need, for a condition that medication won't fix. Pregnancy rewires the immune system in ways you can't predict from one patient to the next, so you need to tell these two conditions apart before you decide on a treatment, and a telehealth allergy platform can help a physician clarify whether symptoms are genuinely allergy-driven before any medication enters the conversation.

There's a deeper layer here that's easy to miss: a mother's allergic state is not sealed off from the fetus. Research from Lisiecka and Luczak (2026) found that maternal IgE, the antibody responsible for allergic reactions, crosses the placental barrier and may sensitize fetal mast cells in utero. The immune conversation happening in the mother's body doesn't stay there.

Clinical Stakes of Poorly Controlled Allergic Disease in Pregnancy

Untreated or poorly managed allergic disease during pregnancy carries documented risks, and avoiding medication altogether is not automatically the safer path. A review in Annals of Allergy, Asthma & Immunology found that asthma exacerbations themselves, not the medications used to prevent them, are the primary driver of adverse pregnancy outcomes. The flare-up is the hazard. The inhaler is not.

Allergic symptoms also reach well past sneezing and a stuffy nose. Severe nasal congestion disrupts sleep, and fragmented sleep during pregnancy compounds fatigue, raises stress, and clouds cognitive function. If a pregnant woman can't breathe through her nose at night, that's more than a minor inconvenience: she accumulates sleep debt on top of a body already working overtime, and unmanaged allergic disease can produce the kind of exhaustion and brain fog that gets written off as "just part of being pregnant.

If you feel foggy, drained, or unable to concentrate during pregnancy, that connection is worth checking. Chronic nasal congestion from allergies fragments your sleep architecture, and fragmented sleep is one of the most direct, well-established causes of daytime fatigue and impaired cognitive function. If the fog and exhaustion began around the same time as congestion, nighttime mouth-breathing, or a new sensitivity to pollen or pet dander, allergic disease is a reasonable place to start looking, and it's a far more fixable cause than "pregnancy exhaustion" treated as a dead end.

Despite the stakes, a substantial share of women with allergies don't see a physician during pregnancy. Lisiecka and Luczak put that figure at around 30%. Part of that gap comes from fear of medication. Part of it comes from underdiagnosis, where congestion or fatigue gets attributed to pregnancy generally instead of being investigated as an allergic symptom. Either way, the patients who could benefit most from monitoring are often the ones who never get evaluated.

If you avoid treatment entirely during pregnancy, that instinct can itself become the risk. The goal isn't abstention. Someone needs to weigh the actual risk of a medication against the actual risk of leaving a condition unchecked, and manage it in proportion to that.

Antihistamine safety and dosing across trimesters

You don't answer antihistamine safety during pregnancy once at the start of nine months as a single yes-or-no question. It shifts by trimester, by drug generation, and by how pregnancy itself changes the way the body processes medication.

Lisiecka and Luczak (2026) documented trimester-specific changes in immune cell activity, including progressive eosinophil suppression across the second and third trimesters. These shifts in the immune landscape are why antihistamine therapy needs a different approach depending on how far along a pregnancy is, not a single rule applied from week one through delivery.

Second-generation antihistamines have the strongest evidence behind them. A 2026 systematic review drew on population cohort data covering more than 1.2 million pregnancies and found no statistically significant association between second-generation antihistamine use and major congenital malformations, spontaneous abortions, or preterm births. Cetirizine and loratadine specifically came out of that review with favorable safety profiles.

First-generation antihistamines, like diphenhydramine, aren't ruled out automatically, but they come with tradeoffs worth weighing against their sedating effects. They cross the blood-brain barrier more readily and sedate you, and that matters when sleep is already compromised by congestion, hormonal shifts, and physical discomfort.

Decongestants need their own caution flag. Wyndly's clinical guidance advises particular care with pseudoephedrine, especially in the first trimester.

Nasal corticosteroid sprays sit in a different category. They act locally, with minimal absorption into the bloodstream, which is a large part of why they're frequently recommended during pregnancy: they sidestep the systemic pharmacokinetic complications that come with oral medications.

None of these categories are interchangeable, and the right choice depends on the trimester, the specific agent, and the individual's broader health picture. That calculation belongs in a conversation with a clinician, not a decision made alone at the pharmacy counter.

Managing asthma during pregnancy: why monitoring, adherence, and escalation willingness matter more than drug avoidance

Asthma is the most serious allergic condition a pregnant woman is likely to manage, and the evidence points toward continuing and optimizing treatment. The risk from an exacerbation consistently outweighs the risk from the medication used to prevent one.

Annals of Allergy, Asthma & Immunology frames optimal asthma care in pregnancy around four pillars: regular review, treatment optimization, management of lifestyle factors and comorbidities, and patient education. That framework treats monitoring and adherence as active clinical work throughout pregnancy, so it isn't a waiting period until delivery.

Objective testing still works, too. The same research confirms pregnancy doesn't significantly alter spirometry or fractional exhaled nitric oxide readings, so clinicians can track asthma control across all three trimesters with tools that stay reliable and consistent, not just by how a patient says she feels.

But testing only helps if patients keep taking their medication, and adherence is the real problem. Medication adherence drops during pregnancy, even among women who were consistent with their asthma treatment beforehand, largely out of fear of fetal harm. JACI In Practice identifies this drop in adherence as a modifiable risk factor, and the data behind that finding show asthma worsening in roughly 30% to 40% of pregnant individuals. To address that drop, the patient and physician need shared decision-making, paired with clear, evidence-based reassurance about what the medications actually do and don't do.

Standard asthma therapies, including inhaled corticosteroids, combination inhalers, and systemic corticosteroids for exacerbations, carry safety profiles that support continued use. The Annals review is direct on this point: these treatments shouldn't be withheld when they're clinically indicated.

For more severe asthma, the same review points to emerging registry data and real-world evidence, backed by international consensus recommendations: when clinically appropriate, biologic therapies may be continued or even started during pregnancy. One advantage of that approach is reducing how much a patient needs to rely on systemic corticosteroids.

Asthma control during pregnancy isn't purely a medication question, either. JACI In Practice points to structural factors, including housing conditions, air pollution exposure, poverty, and obstetric history, as real contributors to how well asthma is controlled. A full management plan accounts for those conditions alongside the pharmacology.

Immunotherapy during pregnancy: what can be continued and what cannot be started

Allergen immunotherapy follows a different rule than antihistamines or asthma medication. Continuing treatment that was already underway before pregnancy is supported by the evidence. Starting it during pregnancy is not recommended. That distinction matters enormously depending on where a patient is in her treatment timeline when she becomes pregnant.

For patients already on maintenance-phase immunotherapy, published clinical guidance supports continuing that treatment through pregnancy, with one caveat: the dose shouldn't be increased further during this period.

The reasoning behind deferring initiation comes down to how immunotherapy works. When you start immunotherapy, you gradually escalate the allergen dose, and that upward titration phase carries the highest risk of a systemic reaction of any point in the treatment course. During pregnancy, a systemic reaction carries added risk to the fetus, so you don't start fresh, but you do continue established treatment.

Subcutaneous immunotherapy (allergy shots) adds a logistical layer on top of the biological one. It requires in-office administration with observation afterward for systemic reactions, and pregnancy doesn't change that. Whether to continue shots or consider switching to a sublingual form is a conversation to have directly with the treating allergist.

Sublingual immunotherapy (SLIT) has a different profile. Available literature describes its safety record as substantially free from serious systemic reactions, and that matters for pregnancy. Even so, the same rule applies: SLIT maintenance can continue in patients already using it, but SLIT should not be started during pregnancy.

For a patient currently managing symptoms with antihistamines or nasal sprays who wants something more lasting than ongoing medication, the best timing is before conception or after delivery. Pregnancy is a reason to plan immunotherapy, not a reason to rule it out.

Wyndly's at-home SLIT model offers one route into that kind of planning: a board-certified physician oversees it, dosing is personalized, and treatment ships directly to the patient. Pricing starts at $99 a month, and the program is FSA/HSA eligible, so cost doesn't have to be the barrier that delays starting treatment once delivery is behind her.

Practical Allergy Management During Pregnancy

Good allergy management during pregnancy works on two tracks at once: reduce allergen exposure and medication risk right now, while using the pregnancy itself as the moment to plan for the longer-term treatment that symptom control alone can't deliver.

Allergen avoidance costs nothing in terms of risk, and you can use it at every stage of pregnancy. Cutting down exposure to dust mites, pet dander, mold, and seasonal pollen lowers the overall allergen load the immune system has to respond to, without requiring any medication decision.

Saline nasal rinses deserve more credit than they usually get. They're safe at any point in pregnancy and mechanically effective at clearing allergen-laden mucus out of the nasal passages, which makes them especially useful when congestion is already being compounded by pregnancy's increased blood flow to mucous membranes.

When symptomatic treatment is needed, a rough priority order holds up well: topical nasal corticosteroids first, given their low systemic absorption; second-generation antihistamines like cetirizine and loratadine next, backed by favorable safety data; and first-generation antihistamines or oral decongestants last, reserved for situations where a clinician has weighed in directly.

Identifying specific allergen triggers, through physician-guided testing done during or even before pregnancy, gives a patient and her care team the information needed to build a real avoidance strategy, and later, a real immunotherapy plan targeted at her actual triggers.

That's really what pregnancy offers here: a forcing function. It's the moment when a lot of women start paying close attention to symptoms they'd normally shrug off, which makes it a natural point to commit to root-cause treatment rather than another year of reaching for whatever antihistamine seems safest. Sublingual immunotherapy has a clinical track record of reducing both symptoms and medication use over a multi-year course, and it can be done from home with physician guidance. Specialized telehealth allergy providers can close the access gap that keeps many pregnant women away from care, offering virtual consultations and personalized guidance without an in-office visit.

Wyndly's virtual consultation model, priced at $49.99 for the initial visit, is built to remove that barrier. You don't need a waiting room to get evaluated and build a treatment plan, so you can start the conversation about long-term allergy treatment as soon as you're ready, even right after delivery.