Map illustration with markers containing peoples facesIt’s well documented that asthma and allergies are more common today than 100 years ago. Why? Doctors and scientists offer a host of theories, including:

Certain risk factors can impact the development and severity of asthma and allergies. These include:

  • the environment in which we live;
  • social and economic factors.

First, let’s look at our environment.

What is the hygiene hypothesis and how does our environment affect asthma and allergies?

Most of us live cleaner lives than our ancestors. Improvements such as good sanitation and safe drinking water have saved countless lives. But is there a flip side to cleanliness? Researchers say yes. They believe the cleaner a child’s early environment, the more likely he or she is to develop asthma and allergies. This is the “hygiene hypothesis.”

The concept was first proposed in the late 1980s by a London doctor named David Strachan. His research found that the more children there are in a family, the lower the rates of asthma and allergies. The idea was that when you have a lot of children in the house, they get – and share – more viruses, bacteria and dirt that develop the immune system.

Since then, the hygiene hypothesis has evolved. It now suggests that infants and young children living in very clean environments are not exposed to enough microorganisms and bacteria. These microorganisms and bacteria are actually helpful. Children get most of them in the womb during pregnancy, from their family members, or in their environment. They live in our guts, skin and airways and play a key role in maintaining our health. They help train our immune systems to withstand viruses, allergens and irritants.

Why do many children living in urban areas have asthma and allergies?

One explanation is the type of bacteria in the environment. Some young children are exposed to more helpful bacteria that can build immunity. Others are exposed to harmful bacteria that predisposes them to asthma and allergies.

Another explanation is greater exposure to viruses in well-populated areas. Respiratory syncytial virus (RSV) is often the first virus infants encounter. This early exposure could cause infection-related cells to become active. When RSV turns into pneumonia, infants are at higher risk for developing asthma.

Further, young children do not have fully developed immune systems. Their body is not yet able to adapt to viruses, allergens and irritants, especially when they infiltrate the lungs. Their immune system cannot provide protection and clear the infection. Their body cannot withstand irritants such as air pollution or chemical cleaning products. All this increases a child’s risk of developing asthma and allergies.

A third explanation? Socioeconomic factors.

How are social and economic issues risk factors for asthma?

Asthma is common in urban areas with high poverty and large minority populations. The rate of emergency department visits and deaths among children with asthma in urban areas is higher than suburban or rural areas. Why is this?

People living in urban areas face environmental allergens and irritants that trigger asthma:

  • indoor mold
  • dust mites
  • cockroaches and mice
  • cigarette smoke
  • air pollution (diesel exhaust from living near highways)

However, a 2015 study from Johns Hopkins Children’s Center shows that living in an urban area by itself may not be a key risk factor for asthma. Income, race and ethnic origin may have more impact on a child’s risk for asthma. In the study, 13 percent of children in cities had asthma, compared with 11 percent living in other areas.

Here’s a closer look at how social determinants of health play a significant role in asthma:

Race and ethnicity

A population-based breakdown of asthma prevalence:

  • People of Puerto Rican descent: 14.9%
  • Black Americans: 10.6%
  • Native Americans and Alaska Natives: 10.2%
  • White Americans: 7.6%
  • Hispanic/Latino Americans: 6.4%
  • Asian Americans: 3.7%

It is clear that Puerto Rican, Black and Native Americans and Alaska Natives share a higher burden of asthma. One reason for this may be genetic and family history of asthma and allergies.

But socioeconomic factors also elevate the risk. These factors may include systemic racism and discriminatory policies. They may impact access to healthcare and support networks.

Low income

Poverty can force people to skimp on healthcare. Or they may choose to forgo or delay preventive medications and health insurance. Children of families living in poverty are more likely to have asthma that need emergency care than children of families with higher incomes.

Education inequality

A lack of understanding of asthma can lead to not following a treatment plan. It can keep people with asthma from knowing how to use inhalers correctly.

Psychosocial stress

Many studies show stress is an asthma trigger. In urban areas, stress can occur in many forms, including violence in a neighborhood. People in unsafe neighborhoods may stay indoors too much and not get enough exercise. They may not feel safe outside or they may not be able to go to parks to relax or play. They may not get enough exposure to helpful bacteria.

Not getting enough vitamin D from sunlight

This can increase the risk of getting viruses and infections that cause or worsen asthma. By staying indoors, young children are not exposed to a natural environment that can lead to an ordered development of the immune system.

Are asthma risk factors less in rural areas?

Some children growing up in rural environments may have a lower risk of asthma and allergies. But the Johns Hopkins study shows that level of risk is not significant. Other studies show rural children who live near urban areas may also be at high risk for asthma.

Rural areas are open land areas with farms, few homes or other buildings, and not very many people. Children growing up in rural areas experience more dirt and animals from an early age.

Mark Holbreich, MD, a board-certified allergist in Indianapolis, provides care to Amish children. He has observed low rates of asthma and allergies in the Amish population. Dr. Holbreich partnered with German pediatrician and allergist Erica Von Mutius, MD, on research comparing Amish children, Swiss children who live on a farm, and Swiss children who don’t live on a farm.

Their research showed positive allergy tests in:

  • 7% of Amish children
  • 22% of children on Swiss farms
  • 45% of non-farm Swiss children

Dr. Holbreich believes the low Amish asthma rates are due to early childhood exposure to farm life, animals, and the foods those animals eat. On Amish farms, barns are often close to homes and new moms often work in the barn alongside their infants. Children with developing immune systems get exposed early on to animals, dust and helpful bacteria.

Does that mean a family should move to a rural area for protection against asthma and allergies? Dr. Holbreich replies no.

“Only very certain unique farming circumstances seem to offer protection. There is no data to suggest that having a more rural life in general is going to make a difference,” he says.

People in rural areas who develop allergic diseases face a different set of triggers. They are likely exposed to more plant and tree pollen, mold and harvest dust. They may be exposed to pollutants from people burning wood or coal for heat.

And air pollution is not only in cities – particles are easily transported by wind to rural areas.

Living in a rural area may also mean families must travel to see asthma and allergy specialists. Primary care doctors can treat allergic diseases, but some may need specialized care. Telemedicine is an option for some people.

What can you do to reduce asthma and allergy triggers in your home?

No matter where you live, there are ways to reduce exposure to asthma and allergy triggers in your home.

State asthma programs and coalitions work with urban and rural communities to conduct home interventions. Counselors and contractors visit homes and apartments to check indoor air quality. They examine burst pipes, leaky windows and roofs for mold. They look at homes holistically for environmental health impacts, with an emphasis on asthma triggers.

Families in need are given tools to help them maintain a healthy indoor environment. These tools include:

  • HEPA (high efficiency particulate air) filters and vacuums to remove allergens and irritants from the air
  • mattress and pillow covers to protect against dust mites
  • nontoxic cleaning materials

Improving energy efficiency in your home is also important. Installing insulation and sealing gaps can reduce a home’s indoor humidity, cold drafts, and allergens such as mold.

Practical tips to reduce asthma and allergy triggers in the home

Here are some strategies to improve indoor air quality in your home.

  • Repair any leaky pipes and leaks in windows and doors to reduce or get rid of mold.
  • Keep gutters clear – another potential source of mold.
  • Use only nontoxic products for pest management.
  • Use a dust-mite-proof mattress and pillow encasements.
  • Use a HEPA vacuum to help prevent allergens from escaping into the air.
  • Use a HEPA air filter in your home and change it every three months.
  • Get rid of wall-to-wall carpeting if possible and use hardwood floors.
  • Take steps to manage pet allergens. Always keep animals out of the bedroom. When brushing them, do it outdoors to keep dander out.
  • Do not leave food out and keep trash cans sealed with heavy lids to reduce pests.
  • Do not use air fresheners, scented cleaning products or candles.
  • Stop smoking, or at least do not smoke in the home or car so the residue doesn’t get into walls or in fabrics. Smokers should change their clothes before being around children.
  • Make sure laundry dryers and kitchen and bathroom fans are venting properly.
  • Talk with your doctor about how to avoid asthma and allergy triggers in your home.


Bradley Chipps, MD, FACAAI, is a board-certified allergist and pediatric pulmonologist with Capital Allergy and Respiratory Disease Center in Sacramento, California. He earned his medical degree from University of Texas Medical Branch in Galveston in 1972. He is Past President of the American College of Allergy, Asthma and Immunology (ACAAI).