Fran Lowry

November 19, 2012

ANAHEIM, California — People with allergies or asthma do not have to remove carpeting from their home as long as it is effectively cleaned, researchers reported here at the American College of Allergy, Asthma & Immunology 2012 Annual Scientific Meeting.

Dr. Vivienne Mahon

"It's a long-held belief that carpets adversely impact allergy and asthma sufferers," Vivienne Mahon, PhD, from Airmid Healthgroup in Dublin, Ireland, told Medscape Medical News.

"We wanted to determine if the often-made recommendation from healthcare providers to people with asthma and allergies to remove carpets for allergen-avoidance purposes is the most appropriate advice," Dr. Mahon said.

Her colleague, Bruce Mitchell, MD, presented data from their study evaluating 9 residential carpets — 6 new and 3 from homes in the United States.

Dr. Bruce Mitchell

Each of the carpets was individually laid in an environmental test chamber under controlled temperature, relative humidity, and air changes per hour. The new carpets were contaminated by introducing aerosolized house dust mite and cat allergens into the chamber.

"The introduction of allergen test dust was not necessary for the 3 used carpets; they contained 'natural' levels of house dust mite and cat allergens," Dr. Mahon explained.

Next, the researchers carried out airborne particle counts and surface and airborne allergen measurements. This was done before and after the carpets were subjected to a cleaning procedure consisting of vacuuming, spraying with a cleaning solution, agitation, and hot water extraction.

They also examined the top, middle, and base layers of the carpets to determine the distribution of allergens.

The researchers found that intensive carpet cleaning was highly effective in reducing both surface allergen and airborne particle counts, and that allergens accumulate in the base of carpets.

On average, airborne particle counts for the artificially contaminated carpets were reduced 5.8-fold after cleaning, and airborne particle counts for the used carpets were reduced 4.3-fold after cleaning.

Additionally, surface cat allergen levels in the new carpets were reduced 37-fold and dust mite allergen levels were reduced almost 10-fold.

"While the study was carried out in an environmental test chamber, the conditions (such as the temperature, relative humidity, and air changes per hour) were chosen to replicate those found in people's homes, and the 3 used carpets were taken from the real-world setting," Dr. Mahon said.

"The size and distribution of particles in the allergen test dust used in the study are comparable to the dust in people's homes, so it represents an appropriate challenge for the carpets. Also, the airborne particle and allergen measurements were taken during real-world-type room disturbances, including walking around the carpeted chamber and bouncing a ball on the carpet," she said.

The data supporting the recommendation that carpets be removed from the homes of people with asthma or allergy are inconsistent, and further research into this area is required, Dr. Mahon added.

These findings "add to an existing body of evidence that indicates that well-maintained and effectively cleaned carpets can contribute to indoor air quality, making them a potential choice for families affected by asthma and allergies. Our hope is that the results will stimulate further debate among healthcare providers and consumers," she said.

"This study demonstrates the importance of regular carpet cleaning with a high-efficiency vacuum for people with allergies," Jay M. Portnoy, MD, professor of pediatrics at University of Missouri, and Mercy Children's Hospital, both in Kansas City, told Medscape Medical News.

Ideally, however, patients with allergies to dust mites and furry animals should live without carpeting, Dr. Portnoy emphasized.

In cases where removal of carpets is not practical, "regular cleaning can reduce allergy exposure substantially," he said.

The study was supported by carpet manufacturer Shaw Industries. Dr. Mahon and Dr. Mitchell are employees of airmid healthgroup, a commercial research organization. Dr. Portnoy reports financial relationships with Thermo Fisher Scientific.

American College of Allergy, Asthma & Immunology (ACAAI) 2012 Annual Scientific Meeting: Abstract 23. Presented November 11, 2012.