Exposure to indoor formaldehyde at allowable levels aggravates symptoms in children with moderate to severe atopic dermatitis (AD), especially in spring and summer, according to a new study.
The study, published in Allergy Asthma and Immunology Research, said minimizing exposure to formaldehyde at any level may be necessary to manage moderate to severe symptoms in children.
Formaldehyde is used in building materials and numerous consumer items such as antiseptics, cleaning agents, carpets, permanent press fabrics, cosmetics, preserved foods, paints, and furniture. The chemical is also widely used in manufacturing processes and is a known environmental pollutant that can cause what is known as sick building syndrome. Studies have already suggested that formaldehyde can cause or aggravate allergic diseases such as asthma and contact dermatitis.
Thirty-six boys and 17 girls with AD and younger than age 18 living in the Seoul, Republic of South Korea, were studied. They were followed from February 2019 to February 2020, and indoor formaldehyde levels in their houses and AD symptoms were measured daily. A total of 4789 person-days of AD symptom data were collected.
When controlling for ambient particulate matter, temperature, and relative humidity, an increase of 10 ppb of formaldehyde increased AD symptoms by 79.2% (95% CI, 19.6%-168.4%) in spring and by 39.9% (95% CI, 14.3%-71.2%) in summer, the study found. In addition, symptoms increased significantly in children aged 6 to 18, the study found, while no such increase was seen in children younger than 6.
Indoor temperature also played a role in increasing symptoms, according to the researchers. When indoor temperature was above 25.5°C (77.9°F), an increase of 10 ppb of formaldehyde increased AD symptoms by 17.8% (95% CI, 3.9%-33.6%).
These study findings may have profound implications for those using World Health Organization (WHO) levels in determining whether children with moderate to severe symptoms can be exposed safely to the chemical. The average value of measured formaldehyde concentrations in the houses of the children studied was 13.6 ppb, far lower than the guideline level recommended by the WHO of 80 ppb and slightly lower than those in European households, which average 16 to 24 ppb, the authors said.
They noted that the WHO guideline was designed to protect against acute and chronic sensory irritations and to prevent cancer.
“However, there is no known threshold of indoor formaldehyde, below which AD symptoms are not affected,” the authors wrote. “It means that the WHO guideline does not reflect the safe level of formaldehyde exposure in patients with AD. Therefore, children with AD need to minimize exposure to even low concentrations of formaldehyde.”
The authors said they were surprised to see indoor formaldehyde concentrations were lower in winter, when there is generally less ventilation, than in spring and summer. However, high indoor temperature can lead to emission of the chemical from walls and furniture, which they indicated might explain the difference. The mean (SD) observed indoor temperature was highest in summer (27.4°C [1.5°C]/81.3°F [34.7°F]), followed by spring (25.6°C [1.7°C]/78.1°F [35.1°F]).
Another unexpected finding was the lack of a significant effect of formaldehyde on AD symptoms in children whose parents smoked, even though the indoor level of the chemical was higher, the authors wrote. In these instances, the mean indoor concentration was 15.5 [15.4] ppb, which might not be high enough to irritate the skin, they noted. The findings that children under age 6 did not have increased symptoms from formaldehyde exposure may be explained by different sensitivities to the chemical, the authors added.
“Minimizing exposure to indoor formaldehyde may be needed for the proper management of AD in children,” they concluded.
Kim Y-M, Kim J, Ha SC, Ahn K. Harmful effect of indoor formaldehyde on atopic dermatitis in children: A longitudinal study. Allergy Asthma Immunol Res. 2021;13(3):468-478. doi:10.4168/aair.2021.13.3.468