How Air Pollution During Pregnancy May Shape a Child’s Allergic Future

By Doanh Nguyen, MD FAAAAI, 04/14/2026

The Invisible Exposure Before Birth

We often think of allergies and asthma as conditions shaped by childhood environment, dust, pets, pollen, or infections. But a growing body of research suggests that the story may begin much earlier, even before a child takes their first breath.

A study published in Environmental Pollution followed a large group of mothers and children in rural and urban France and found that air pollution exposure during pregnancy, particularly fine particulate matter (PM₂.₅) and nitrogen dioxide (NO₂), may influence a child’s risk of developing asthma, eczema, and allergic rhinitis later in life.

Even more striking: these effects were observed in a region considered relatively “low pollution.”

Pollution and the Developing Immune System

During pregnancy, the developing fetus is not as shielded from the outside world as once believed. Tiny airborne particles, particularly fine particulate matter (PM₂.₅) and nitrogen dioxide (NO₂), often generated by traffic and industrial activity, can enter the maternal bloodstream and reach the placenta. From there, they may influence fetal development in ways that are only now being understood.

These pollutants can trigger inflammatory responses and oxidative stress, altering how the immune system matures. They may also leave epigenetic marks, chemical changes that affect how genes are expressed, potentially predisposing the child to allergic conditions long after birth.

Urban vs. Rural: Not All Air Is the Same

The study offers a particularly revealing comparison between urban and rural environments. Although most participants lived outside major cities, children growing up in urban settings showed clearer associations between prenatal pollution exposure and allergic disease.

By the age of six, urban children exposed to higher pollution levels during pregnancy were more likely to develop eczema. This pattern suggests that the type, concentration, and mixture of pollutants in cities, especially those related to traffic, may carry distinct biological consequences compared with rural exposures.

“Low Pollution” May Not Be Low Enough

Perhaps the most unsettling insight is that the pollution levels observed in the study were not extreme. In fact, they would be considered moderate by many international standards. Yet these levels still exceeded the latest recommendations from the World Health Organization, and they were sufficient to show measurable associations with disease.

This raises an important possibility: there may be no truly safe level of exposure during pregnancy. Even modest elevations in air pollution could have lasting effects on a developing child.

A Delayed Timeline of Disease

One of the more subtle findings is that the effects of prenatal exposure do not always appear immediately. At age six, the associations were most apparent for eczema, particularly in urban children. But by age twelve, the data began to show increasing tendencies toward asthma and the coexistence of multiple allergic conditions.

This delayed emergence suggests that early exposure may quietly shape the immune system, with disease manifesting only later as additional environmental or biological pressures accumulate.

Why This Matters for Public Health

These findings align with a broader scientific framework known as the developmental origins of health and disease, the idea that early life environments, including those experienced in the womb, can influence health trajectories across a lifetime. Air quality, in this context, becomes more than an environmental concern; it becomes a prenatal health factor.

The study underscores the importance of rethinking pollution standards and highlights the need to protect vulnerable populations, especially pregnant individuals, even in areas not typically considered high risk.

The Bigger Picture

Taken together, the research suggests that allergic diseases are not simply the result of genetics or postnatal exposures. They are, in part, shaped by invisible influences long before birth. In that earliest stage of life, when organs are forming and the immune system is learning how to respond to the world, something as commonplace as the air we breathe may leave a lasting imprint.

Reference

1. Patlán-Hernández AR, Savouré M, Audureau E, et al. Associations of exposure to outdoor PM2.5 and NO2 during pregnancy with childhood asthma, rhinitis, and eczema in a predominantly rural French mother-child cohort. Environ Pollut. 2024;363(Pt 2):125206. doi:10.1016/j.envpol.2024.125206

2. World Health Organization. WHO global air quality guidelines: particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. Geneva: World Health Organization; 2021.

3. Hehua Z, Qing C, Shanyan G, Qijun W, Yuhong Z. The impact of prenatal exposure to air pollution on childhood wheezing and asthma: A systematic review. Environ Res. 2017;159:519-530. doi:10.1016/j.envres.2017.08.038

4. Miller RL, Peden DB. Environmental effects on immune responses in patients with atopy and asthma. J Allergy Clin Immunol. 2014;134(5):1001-1008. doi:10.1016/j.jaci.2014.07.064

5. Barker DJ. The developmental origins of adult disease. J Am Coll Nutr. 2004;23(6 Suppl):588S-595S. doi:10.1080/07315724.2004.10719428