Pollen, mites and pet allergy sufferers can breathe a sigh of relief — air humidity helps them all!
House dust is the biggest trigger of allergies worldwide. Anyone who is allergic to house dust reacts to either mite constituents or animal allergens with complaints such as sneezing, eye irritations or asthma. Together with pollen allergy sufferers, these people experience symptoms when exposed to airborne, allergy-triggering substances, known as allergens.
Pollen allergy sufferers know what alleviates their complaints: rain, humid air and the absence of wind. House dust allergy sufferers experience significantly pronounced complaints during the dry hot period. The experts say to them: Be careful with humidity — 30 or 40 percent is better than 50 percent! Is that right?
It is logical that only the proportion of house dust that is present in the air can be responsible for complaints and illness. This proportion is difficult to measure. One year ago a study was published for the first time, in which the quantity of mite allergens effectively breathed in by 10 individuals during normal activities was measured over 24 hours . The study shows that the quantity breathed in primarily depends on those personal activities that lead to dust turbulence. When the activity is low (sleeping), a minimum of mite allergens is breathed in. Among people who are engaged in physical movement and activity, the concentration in the air they breathe in rises by over a thousand times!
The procedure of dust turbulence is a key aspect for the impact and thus the complaints and clinical pictures. A few weeks ago, a study was published which showed that the turbulence of mite constituents from a linoleum floor continually decreases by about one hundred times if the air humidity is increased from 10% to 40% and 80% . This corresponds to our day-to-day experience and explains why dryness exacerbates allergy complaints.
Leaflets recommend that allergy sufferers keep air humidity in their apartments below an upper limit of 50 percent. Some recommendations specify a lower limit of between 35 and 40 percent. It is not mentioned that, for three quarters of the year, this upper limit is exceeded in our houses. Nor is it mentioned that in the vast majority of buildings (old, but especially new buildings) the lower limit is significantly undercut during the winter months. Monthly average values of 20 percent have become normal . Since this pronounced dryness facilitates house dust turbulence, it leads to an increase of allergic complaints in wintertime [2, 4].
The air humidity plays a major role in the extent of dust turbulence. Experiments show that the adhesion of “moistened” dust to smooth floor surfaces increases dramatically above 30 to 40 percent. In this area, the weight of the dust particles also increases drastically due to water condensation. They stick together, form clusters, and quickly fall to the floor again (see pictures). Apart from that, the risks of mold problems increase above 60% humidity. The optimal humidity range for minimizing allergy complaints is therefore between 40 and 60 percent. Allergy sufferers should monitor the air humidity in winter using a hygrometer. To find out how to uphold the upper limit and humidify the air in a hygienic manner, see the box titled “Air humidity”.
Precisely measuring the proportion of allergens that reach our airways via the ambient air is complicated and expensive . The only measuring instrument which is permanently available for real-time measurement of the impact are the mucous membranes in the nose, airways and eyes. Trust these sensations, take responsibility for yourself and decide what does and does not help you!
 Tovey ER et al, Time-Based Measurement of Personal Mite Allergen Bioaerosol Exposure over 24 Hour Periods, PLoS ONE, 2016
 Salimifarad P et al, Resuspension of biological particles from indoor surfaces: Effects of humidity and air swirl, Science of the Total Environment 583 (2017) 241–247
 Quinn A, Shaman J, Indoor temperature and humidity in New York City apartments during winter, Science of the Total Environment 583 (2017) 29–35
 Tian Y et al, A comparative study of walking-induced dust resuspension using a consistent test mechanism, Indoor Air 2014
 Naclerio RM, Observations on the ability of the nose to warm and humidify inspired air, Rhinology, 45, 2007