significance of humidity and temperature on skin and upper airway symptoms

Signicance of humidity and temperature on skin and upper airway

symptoms

Introduction

With air-conditioning, temperature and humidity are,despite air change rate and airow velocity, basicphysical elements aecting human comfort inside abuilding. Absolute humidity is the content of watervapor in the air (expressed, e.g. in vapor pressure, hPa,g H2O/kg air). Relative humidity (%) is the ratio of theactual vapor pressure and the saturation vapor pres-sure, which is an exponential function of air tempera-ture. Temperature and humidity aect the thermalbalance of the human body via respiratory organs andskin (Hoppe, 1983). They also regulate human comfortboth directly via thermal sensations and indirectly bychanging the perceived indoor air quality parameterssuch as stuness (Berglund and Cain, 1989). We havestudied the eect of humidication on skin and airway

symptoms, and on perceived indoor air quality. Wefound that during the heating season in Finland,humidication alleviates dryness symptoms of skin andupper airways in oce environments and excessiveindoor air temperature increases unpleasant symptomsof the upper respiratory tract and skin (Palonen et al.,1993; Reinikainen et al., 1991, 1992).According to the research of Hoppe, air humidity is

the most important physical factor aecting energybalance of the upper respiratory tract. Inhalingrequires energy for humidifying the air, which undermost conditions including the oce environment is farfrom the saturation humidity, to relative humidity of100% in the core temperature of 37C. Some energy isgained in exhaling, when a portion of the humiditycondenses on surfaces of the mucosa. Energy loss fromupper airways depends on both absolute and relative

Abstract The objective of the present study was to assess the eect of absoluteand relative humidity, temperature and humidication on workers skin andupper airway symptoms, and perceptions in the oce environment. Associationsbetween physical factors, and symptoms and perceptions were assessed in logisticregression models. At temperatures between 18 and 26C, relative humidity of1740%, and absolute humidity of 3.35.6 g H2O/kg air, skin symptoms andnasal dryness and congestion were alleviated by both kinds of humidity. Pha-ryngeal dryness increased when temperatures rose and was alleviated with a risein relative humidity. Eye symptoms showed no dependence on humidity. Anykind of humidity increased odor sensation. Stuness increased when the air washumidied. In non-humidied conditions (21.322.7C, 20.031.7%, 3.35.6 gH2O/kg air), skin and nasal symptoms showed no association with humidity ortemperature. Pharyngeal dryness diminished when humidity rose. In addition,the association between humidity and odor disappeared. In humidied condi-tions (21.523.7C, 26.641.2%, 4.27.0 g H2O/kg air), nasal dryness and con-gestion were alleviated by both absolute and relative humidity, and odorperception increased. Skin dryness and rash, pharyngeal dryness, and nasaldryness and congestion are alleviated in higher humidity. Steam humidicationresults in a risk for increased perception of odor and stuness.

L. M. Reinikainen1,2,J. J. K. Jaakkola1,2,31Department of Public Health, P.O. Box 41, University ofHelsinki, Helsinki FIN-00014, Finland, 2Laboratory ofHeating, Ventilating and Air-Conditioning, Faculty ofMechanical Engineering, Helsinki University ofTechnology, P.O. Box 4100, Helsinki FIN-02015, Finland,3The Institute of Occupational Health, The University ofBirmingham, Edgbaston, Birmingham B15 2TT, UnitedKingdom

Key words: Indoor air; Office environment; Sick buildingsyndrome; Humidity; Humidification; Temperature.

Leena M. ReinikainenDepartment of Public Health, P.O. Box 41, University ofHelsinki, Helsinki FIN-00014, FinlandFax: 358 0 27540e-mail: [email protected]

Received for review 20 September 2000.Accepted for publication 25 May 2001 Indoor Air (2003)

Practical ImplicationsIn cold climates, dry air seems to be related to skin symptoms and nasal dryness. Skin symptoms may be alleviated bylowering room temperature which increases relative humidity. Nasal dryness is more dependent on absolute humidity.Steam humidication includes a risk of feeling the air more stuy.

Indoor Air 2003; 13: 344352www.blackwellpublishing.com/inaPrinted in Denmark. All rights reserved

Copyright Blackwell Munksgaard 2003INDOOR AIR

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humidity because it is dependent also on ambienttemperature (Hoppe, 1983). Hoppe and Martinac havepostulated that evaporation from dierent parts of skinis dependent on whether the area is covered withclothing. Evaporation from clothed skin is moredependent on absolute than relative humidity. Bareskin, such as the head, has a temperature closer to thetemperature outside the body, and thus, the evapor-ation is more dependent on relative humidity (Hoppeand Martinac, 1998). Sommer and coworkers havestudied the stability of the tear lm in oce conditions.They found that in dry climates the breakup time of thetear lm is reduced, causing a phenomenon known asthe oce eye syndrome (Sommer et al., 1994). Anassociation also appears to exist in the oce environ-ment between eye and throat irritations, and anincrease in reported eye irritations at temperaturesbetween 22 and 26C (Backman and Haghighat, 1999).The objective of our study was to investigate the

relationship of symptoms and perceptions reported byworkers to temperature, and to the absolute andrelative humidity in oce environment. We presumedthat some of the symptoms, such as sensation ofdryness of mucosa and eyes, and skin symptoms, areassociated with a loss of energy from the correspond-ing part of the body. Some others such as nasaldripping would reect the condensation of watervapor on the mucosa. We also wanted to analyze therole of humidication itself on the symptoms andperceptions.

Methods

A 6-week cross-over study was conducted in 1989 inthe Pasila Oce Center by changing humidicationand studying corresponding changes in the symptomsand perceptions of the occupants. The building consistsof six symmetrical wings joined by a central part(Figure 1). This study was conducted in the threenorthern wings of the building (A, B, and C).The wingscomprise small oces on oors 38 which wereincluded in the study. Two of the wings (A and B)were humidied with steam humidication, and thethird wing (C) on the same side of the building wasused as a non-humidied reference. The humidicationtook place for one week in each of the wings ofexperiment. Changes in humidication were conductedduring the weekends representing the washout period.In the third wing (C), personal data and air qualitymeasurements were similarly collected, but the wingwas not humidied (Reinikainen et al., 1992).The data concerning symptoms and perceived indoor

air quality were received from structured diaries whichthe participants lled in every afternoon. The symp-toms were coded from 0 for none to 3 for strongsymptoms. Odor and stuness were coded from 0 to 5.The diary also comprised questions concerning symp-

toms of upper respiratory infections. Answers fromdays of any symptoms of infection were rejected fromthe analysis, and the workers had to have spent at least2 h in their oce to be accepted in the analysis.In connection with the humidication trial, relative

humidity and temperature were measured continuouslyin all three wings in two or three oces givinginformation on relative humidity and temperature inthe corresponding wing. In addition, each participantreceived a dry bulb thermometer whose reading wasregistered in connection of lling in the symptom diary.Thus, we received a detailed picture of the participantsexposure to both humidity and temperature. Based onthe diagrams constructed for the calculation of airhumidity (Molliers diagram), we rst calculated theabsolute humidity of each day of the study from theregistrations of the continuous measurements. Next,we calculated the relative humidity in each oce basedon the daily temperature data registered by theparticipants.

Indoor air quality

The air change was measured in each room in everywing before the beginning of the study. Chemical andbiological impurities measured were formaldehyde,fungal spores and growth, bacterial concentration,and the total amount of suspended particles, as thesewere suspected to be aected by the humidication. Airsamples for formaldehyde, fungal spores, and bacteriawere gathered from a sample of oces both during andwithout humidication. In addition, surface samples fordetecting possible fungal growth were gathered fromthe ventilation pipelines. The total amount of dust wascollected from the intake and outlet conducting pipe-

Fig. 1 Pasila Oce Center, experiment wings A and B, andcontrol C

Eect of humidity and temperature on skin and upper airway symptoms

345

lines in the wings of the humidication experiment andthe outlet pipeline in the reference wing.

Statistical methods

Answers for symptoms and perceptions were dicho-tomized (no symptoms, no odor or stuness 0, anydegree of symptoms, any odor or stuness 1) andassociations between them and humidity were assessedin logistic regression models using a repeated meas-urements technique to take into account the dierentnumber of answers received from individuals.Associations between symptoms and perceptions,

and the exposure to either absolute or relativehumidity, temperature and humidication wereassessed in logistic regression models including anindicator variable in order to take into account theuneven number of answers received from the indi-viduals (max 30, min 1).The associations were assessed in four types of

models. The rst model contained one of the twohumidity types from each individuals oce, thecorresponding temperature in the oce, and humidi-cation. The second model assessed absolute or relativehumidity stratied with temperature. The third modelassessed absolute or relative humidity, taking intoaccount the presence or absence of humidication, andthe fourth model contained only the absolute orrelative humidity. Odor and stuness were connectedwith how long the workers had their windows open,and this time was taken into these models as aconfounding factor. In addition, two sets of modelswere calculated using either humidied conditions(wings A and B) or non-humidied conditions (wingsA, B, and C). All calculations were made with the SPSSstatistical package release 8.0.

Results

Study population

A total of 368 workers (71.2%) returned the baselinequestionnaire and at least one of the diaries withinformation on any of the symptoms or perceptions

of interest, sucient information on the possiblesymptoms of respiratory infection, and had spent atleast 2 h in their oce. In all, 342 diaries werereceived from non-humidied and 233 from humid-ied conditions.

Temperature and humidity

The mean temperature according to the continuousmeasurements collected during the non-humidiedperiod in wings A and B and the total period in C was21.9C (21.322.7C), and during the humidied periodin A and B, 22.4C (21.523.7C). The mean relativehumidity was 25.8% (20.031.7%) and 32.7% (26.641.2%) for non-humidied and humidied conditions,respectively. The corresponding absolute humiditieswere 4.2 (3.35.6) and 5.6 (4.27.0). More detailed dataof temperature and humidity are given in Table 1.

Ventilation rate and air impurities

The ventilation rate was in average very high, 770 l/sfor each person (mean 24; s.d. in the trial area 9.9 l/sfor each person). The formaldehyde concentrationswere all below 0.1 mg/m3, and there was no associ-ation with humidication. Concentrations of particles,bacteria, and fungal spores in the building were low.The species of the fungi were the same which arepresent in the outdoor air. The surface samples didnot show any fungal growth. No major dierencesoccurred between the three wings in any of theconcentrations.

Associations between symptoms and physical indoor air conditions

The associations between symptoms and physicalindoor air conditions, including humidity, temperature,and humidication, are shown in Tables 2 and 3, theformer focusing on absolute humidity and the latter onrelative humidity, both including the total population.Tables 4 and 5 contain the associations betweenabsolute and relative humidity, and temperature sep-arately in non-humidied and humidied conditionscorrespondingly.

Table 1 Temperatures, and absolute and relative humidity in the Pasila Office Center; mean (range)

Continuous measurements Conditions in individual offices

Wing Temperature (C) Relative humidity (%) Absolute humidity (g H2O/kg air) Temperature (C) Relative humidity (%)

Non-humidifiedA 21.5 (21.322.5) 25.4 (21.231.7) 4.1 (3.55.3) 21.9 (19.025.0) 24.8 (17.439.9)B 22.4 (22.022.7) 25.0 (20.030.2) 4.3 (3.35.6) 22.8 (18.025.0) 24.6 (16.637.3)C 21.8 (21.322.2) 26.4 (21.231.4) 4.3 (3.55.2) 22.4 (18.025.0) 24.9 (16.638.0)

HumidifiedA 22.0 (21.822.3) 34.3 (31.741.2) 5.7 (5.26.9) 22.2 (19.026.0) 34.0 (27.949.1)B 22.8 (21.523.7) 31.1 (26.638.3) 5.4 (4.27.0) 23.0 (19.526.0) 30.8 (22.244.2)

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Skin symptoms seemed to be alleviated by increasingany type of humidity. The association with relativehumidity was slightly stronger. The eect was constantin all conditions though the association was statisti-cally signicant only in the total population, and inmodels containing either the humidity alone or humid-ity and temperature. In models containing the humid-ication, the eect of humidity disappeared. As a rule,high temperature increased the sensation of skindryness. In the non-humidied conditions the eect

was opposite. Skin rash was alleviated on temperatureincrease in all but the humidied conditions. Theassociation between temperature and skin symptomswas not statistically signicant.Eye dryness was also constantly alleviated by

humidity, though the eect was not statistically signi-cant in any of the models. Humidication also had analleviating eect, though not statistically signicant.High temperature either had no eect or alleviated eyedryness.

Table 2 Associations between absolute humidity and temperature, and skin, eye and upper airway symptoms, odor and stuffiness in the total population; logistic regression; odds ratio(OR) per 1 g H2O/kg air and 1C

Absolute humidity Temperature Humidification

Outcome Model number OR 95% CI OR 95% CI OR 95%CI

Skin dryness 1 0.81 (0.621.06) 1.19 (0.911.55) 0.88 (0.521.51)2 0.79 (0.650.95)* 1.14 (0.881.48)3 0.81 (0.621.06) 0.93 (0.551.58)4 0.80 (0.660.96)*

Skin rash 1 0.81 (0.551.19) 0.78 (0.521.16) 0.60 (0.261.37)2 0.70 (0.510.95)* 0.78 (0.521.15)3 0.81 (0.551.19) 0.59 (0.261.33)4 0.69 (0.510.94)

Eye dryness 1 0.96 (0.741.25) 1.00 (0.771.31) 0.80 (0.481.33)2 0.96 (0.741.25) 1.01 (0.771.31)3 0.96 (0.741.25) 0.80 (0.481.33)4 0.89 (0.741.07)

Pharyngeal dryness 1 0.83 (0.631.11) 1.09 (0.841.43) 1.09 (0.582.05)2 0.87 (0.701.07) 1.11 (0.851.44)3 0.84 (0.631.11) 1.12 (0.602.09)4 0.88 (0.711.08)

Nasal dryness 1 0.74 (0.570.95)* 1.28 (0.991.67) 0.86 (0.521.42)2 0.71 (0.590.85)* 1.26 (0.971.63)3 0.74 (0.570.95)* 0.92 (0.561.52)4 0.72 (0.610.86)*

Nasal congestion 1 1.02 (0.771.34) 1.34 (1.011.79) 0.51 (0.280.91)*2 0.84 (0.681.03) 1.30 (0.991.72)3 1.03 (0.781.35) 0.54 (0.300.96)*4 0.86 (0.701.05)

Nasal excretion 1 1.05 (0.731.50) 0.71 (0.491.04) 0.81 (0.351.87)2 0.98 (0.741.31) 0.70 (0.491.02)3 1.03 (0.721.48) 0.72 (0.321.65)4 0.94 (0.711.25)

Sneezing 1 1.24 (0.921.68) 0.72 (0.530.98)* 1.38 (0.633.02)2 1.34 (1.041.72)* 0.73 (0.540.99)*3 1.23 (0.911.66) 1.27 (0.59-2.74)4 1.30 (1.011.67)*

Odora 1 1.36 (1.041.79)* 1.09 (0.791.49) 0.96 (0.541.70)2 1.33 (1.111.61)* 1.09 (0.811.48)3 1.36 (1.041.79)* 0.99 (0.561.73)4 1.34 (1.121.62)*

Stuffinessa 1 1.13 (0.911.40) 1.13 (0.891.45) 1.71 (1.112.65)*2 1.35 (1.161.58)* 1.12 (0.931.51)3 1.13 (0.911.40) 1.76 (1.142.71)*4 1.37 (1.171.60)*

Models: 1, absolute humidity + temperature + humidification; 2, absolute humidity + temperature; 3, absolute humidity + humidification; 4, absolute humidity.a Controlled for the number of hours people had their windows open daily.* P < 0.05.


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Pharyngeal dryness was slightly increased by higherhumidity, and increased by high temperature. In thenon-humidied conditions the eect of temperaturewas opposite. Humidication increased pharyngealdryness. None of the eects was statistically signicant.Nasal dryness was alleviated by an increase in

humidity of any kind in all but the non-humidiedconditions, and the alleviating eect was statisticallysignicant. High temperature increased nasal dryness,and humidication decreased it. These eects were notstatistically signicant.

Nasal congestion was constantly decreased byhumidication, and the eect was statistically signi-cant in all models containing the humidication. Inhumidied conditions, both types of humidity seemedto have a statistically signicant alleviating eect ifthey were in the model alone. High temperatureincreased nasal congestion, and the eect was statis-tically signicant in the models containing eitherabsolute or relative humidity, temperature, andhumidication. In humidied conditions the associ-ation was statistically signicant in the model

Table 3 Associations between relative humidity and temperature, and skin, eye and upper airway symptoms, odor and stuffiness in the total population; logistic regression; OR per %relative humidity (RH) and 1C

Relative humidity Temperature Humidification

Outcome Model number OR 95% CI OR 95% CI OR 95% CI

Skin dryness 1 1.00 (0.921.08) 1.20 (0.911.54) 0.84 (0.501.43)2 0.96 (0.930.99)* 1.13 (0.881.47)3 0.97 (0.921.02) 0.89 (0.531.50)4 0.96 (0.931.00)*

Skin rash 1 0.96 (0.901.04) 0.77 (0.521.15) 0.59 (0.261.35)2 0.94 (0.881.00)* 0.77 (0.521.14)3 0.96 (0.901.04) 0.57 (0.251.30)4 0.94 (0.880.99)*

Eye dryness 1 0.99 (0.951.04) 1.00 (0.771.31) 0.80 (0.481.32)2 0.98 (0.951.01) 1.00 (0.771.31)3 0.99 (0.951.04) 0.80 (0.481.32)4 0.98 (0.951.01)

Pharyngeal dryness 1 0.96 (0.911.01) 1.09 (0.841.42) 1.12 (0.602.08)2 0.97 (0.931.01) 1.11 (0.851.44)3 0.96 (0.921.02) 1.15 (0.622.12)4 0.97 (0.931.01)

Nasal dryness 1 0.95 (0.911.00)* 1.28 (0.981.66) 0.80 (0.481.33)2 0.94 (0.910.97)* 1.24 (0.961.61)3 0.95 (0.911.00)* 0.87 (0.531.42)4 0.95 (0.910.98)*

Nasal congestion 1 1.01 (0.961.06) 1.34 (1.011.78)* 0.50 (0.280.89)*2 0.97 (0.931.01) 1.29 (0.981.71)3 1.01 (0.961.06) 0.53 (0.300.95)4 0.97 (0.941.01)

Nasal excretion 1 0.99 (0.931.06) 0.71 (0.491.04) 0.90 (0.392.06)2 0.99 (0.941.04) 0.71 (0.491.03)3 0.99 (0.931.06) 0.99 (0.931.06)4 0.98 (0.931.03)

Sneezing 1 1.05 (1.001.11) 0.72 (0.530.98)* 1.28 (0.5892.78)2 1.06 (1.021.11)* 0.73 (0.540.99)*3 1.05 (0.991.11) 1.17 (0.542.51)4 1.06 (1.011.11)*

Odora 1 1.07 (1.021.13)* 1.10 (0.801.51) 0.87 (0.491.55)2 1.06 (1.021.10)* 1.09 (0.811.48)3 1.07 (1.021.13)* 0.90 (0.511.58)4 1.06 (1.031.10)*

Stuffinessa 1 1.03 (0.991.07) 1.13 (0.891.45) 1.65 (1.062.55)*2 1.06 (1.031.09)* 1.19 (0.941.51)3 1.03 (0.991.07) 1.70 (1.102.62)*4 1.06 (1.031.10)*

Models: 1, relative humidity + temperature + humidification; 2, relative humidity + temperature; 3, relative humidity + humidification; 4, relative humidity.a Controlled for the number of hours people had their windows open daily.* P < 0.05.


348

containing absolute humidity and temperature orrelative humidity alone.Nasal excretion showed no constant patterns other

than the non-signicant alleviating eect of humidi-

cation. Sneezing was alleviated in higher temperatures,and increased in higher humidity. The eect oftemperature was statistically signicant in the totalpopulation, and the eect of any kind of humidity also

Table 5 Associations between absolute and relative humidity and temperature, and skin, eye and upper airway symptoms, odor and stuffiness in the humidified conditions; logisticregression; OR per 1 g H2O/kg air, %RH, and 1C

Absolute humidity Temperature Relative humidity Temperature

Outcome Model OR 95% CI OR 95% CI Model OR 95% CI OR 95% CI

Skin dryness Hat 0.82 (0.501.34) 1.77 (1.003.13) Hrt 0.97 (0.891.07) 1.70 (0.923.16)Ha 0.76 (0.471.23) Hr 0.94 (0.861.02)

Skin rash Hat 0.86 (0.372.00) 2.29 (0.766.95) Hrt 0.97 (0.811.15) 2.17 (0.677.04)Ha 0.80 (0.361.79) Hr 0.93 (0.791.09)

Eye dryness Hat 0.73 (0.441.23) 0.88 (0.431.78) Hrt 0.95 (0.871.05) 0.81 (0.391.70)Ha 0.74 (0.441.24) Hr 0.96 (0.881.06)

Pharyngeal dryness Hat 0.85 (0.471.54) 1.47 (0.772.79) Hrt 0.95 (0.851.06) 1.32 (0.662.63)Ha 0.83 (0.461.48) Hr 0.93 (0.841.04)

Nasal dryness Hat 0.42 (0.250.69)* 1.15 (0.622.13) Hrt 0.85 (0.780.93)* 0.85 (0.441.67)Ha 0.41 (0.250.66)* Hr 0.86 (0.790.93)*

Nasal congestion Hat 0.50 (0.241.05) 2.43 (1.045.68)* Hrt 0.89 (0.781.02) 1.96 (0.794.88)Ha 0.44 (0.220.92)* Hr 0.85 (0.750.97)*

Nasal excretion Hat 1.32 (0.612.90) 1.32 (0.612.90) Hrt 1.04 (0.901.21) 0.47 (0.121.87)Ha 1.33 (0.612.93) Hr 1.06 (0.921.23)

Sneezing Hat 1.62 (0.813.22) 0.66 (0.261.65) Hrt 1.12 (0.981.28)* 0.80 (0.302.13)Ha 1.69 (0.853.34) Hr 1.13 (1.001.28)*

Odora Hat 3.23 (1.915.44)* 0.79 (0.371.68) Hrt 3.27 (1.945.52)* 1.19 (0.542.63)Ha 3.27 (1.945.52)* Hr 1.24 (1.131.36)*

Stuffinessa Hat 0.95 (0.661.36) 1.27 (0.702.30) Hrt 0.99 (0.921.06) 1.24 (0.672.30)Ha 0.94 (0.651.35) Hr 0.98 (0.921.05)

Models: Hat, humidified, absolute humidity + temperature; Ha, humidified, absolute humidity; Hrt, humidified, relative humidity + temperature; Hr, humidified, relative humidity.a Controlled for the number of hours people had their windows open daily.* P < 0.05.

Table 4 Associations between absolute and relative humidity and temperature, and skin, eye and upper airway symptoms, odor and stuffiness in the non-humidified conditions; logisticregression; OR per 1 g H2O/kg air, %RH, and 1C

Absolute humidity Temperature Relative humidity Temperature

Outcome Model OR 95% CI OR 95% CI Model OR 95% CI OR 95% CI

Skin dryness nHat 0.76 (0.531.07) 0.99 (0.721.35) nHrt 0.98 (0.931.03) 0.94 (0.681.30)nHa 0.76 (0.531.07) nHr 0.98 (0.931.04)

Skin rash nHat 0.74 (0.461.20) 0.66 (0.411.05) nHrt 0.96 (0.891.04) 0.60 (0.370.98)nHa 0.72 (0.451.16) nHr 0.98 (0.911.06)

Eye dryness nHat 0.97 (0.691.37) 0.96 (0.711.31) nHrt 0.97 (0.921.03) 0.92 (0.671.26)nHa 0.97 (0.691.36) nHr 0.98 (0.931.03)

Pharyngeal dryness nHat 0.78 (0.551.11) 0.93 (0.681.26) nHrt 0.95 (0.901.00) 0.83 (0.601.15)nHa 0.77 (0.551.10) nHr 0.95 (0.911.01)

Nasal dryness nHat 1.02 (0.731.43) 1.22 (0.891.69) nHrt 1.02 (0.961.07) 1.26 (0.901.76)nHa 1.04 (0.741.45) nHr 1.01 (0.961.06)

Nasal congestion nHat 1.24 (0.891.71) 1.22 (0.891.69) nHrt 1.00 (0.951.05) 1.23 (0.891.72)nHa 1.26 (0.911.74) nHr 0.99 (0.941.04)

Nasal excretion nHat 0.90 (0.591.38) 0.68 (0.451.03) nHrt 0.98 (0.921.05) 0.66 (0.431.01)nHa 0.88 (0.581.34) nHr 1.00 (0.941.07)

Sneezing nHat 1.15 (0.811.62) 0.70 (0.500.98) nHrt 1.02 (0.971.08) 0.74 (0.521.05)nHa 1.13 (0.801.60) nHr 1.04 (0.991.09)

Odora nHat 0.90 (0.591.36) 1.40 (0.932.09) nHrt 0.97 (0.901.04) 1.31 (0.862.00)nHa 0.90 (0.591.37) nHr 0.95 (0.891.02)

Stuffinessa nHat 1.06 (0.781.45) 0.90 (0.661.21) nHrt 1.00 (0.951.05) 0.89 (0.651.23)nHa 1.06 (0.771.44) nHr 1.00 (0.961.05)

Models: nHat, non-humidified, absolute humidity + temperature; nHa, non-humidified, absolute humidity; nHrt, non-humidified, relative humidity + temperature; nHr, non-humidified,relative humidity.a Controlled for the number of hours people had their windows open daily.* P < 0.05.


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in the total population in the models not containinghumidication.The sensation of odor was increased by humidity.

The eect was statistically signicant in the totalpopulation in all models. The association with absolutehumidity was slightly stronger compared to the relativehumidity. In the total population, association betweenodor and humidication was non-signicant andshowed a decrease in the sensation of odor duringhumidication. There was a non-signicant directassociation with temperature. In the non-humidiedconditions the associations with humidity or tempera-ture were not signicant.Stuness seemed to be associated with humidica-

tion in the total population. Humidication increasedthe sensation of stuness. The eects of hightemperature and an increase in both absolute andrelative humidity had the same direction in the totalpopulation. The association to temperature was notsignicant, and the association to humidity wasstatistically signicant only if humidication was notin the model. In non-humidied conditions, theassociation with temperature was opposite to thetotal population and humidied conditions. In humid-ied conditions, stuness and humidity had a reverseassociation. These associations were not statisticallysignicant.As a summary, it seemed that in the non-humidied

conditions (temperature 1825C, absolute humidity3.55.6 g water/kg air, and relative humidity 2032%),no statistically signicant associations were foundbetween humidity and temperature, and the symptomsof upper airways or odor or stuness. In the humid-ied conditions (temperature 1926C, absolutehumidity 4.27.0 g water/kg air, and relative humidity2741%), statistically signicant increase was foundbetween odor and sneezing, and decrease between nasaldryness and congestion and humidity. In humidiedconditions, nasal congestion was increased by hightemperature, and the association was statisticallysignicant in the model containing absolute humidityand temperature. Having the total population in themodels assessing the associations between absolute orrelative humidity, and temperature and humidication,skin symptoms showed a decrease when humidity washigher, but only the models not containing humidi-cation were statistically signicant. The associationwith absolute humidity was stronger. Nasal drynessseemed to be constantly alleviated by humidity, abso-lute humidity having a stronger eect. Nasal conges-tion was alleviated by humidication, and hightemperature increased it. The sensation of odor wasconsistently increased by humidity, and the associationwas stronger with absolute humidity. Stuness showedan association with humidication, and there wasassociation with humidity only in the models wherehumidication was not present.

Discussion

We studied the inuence of temperature and humidityunder real-life conditions in the oce environment. Inaddition to our previous report (Reinikainen et al.,1992) we included in the analysis, the population in theC wing, who were only exposed to the natural variationin humidity. Although the control of environmentalconditions was poorer than in a laboratory setting, thendings are expectedly more relevant and describe theconditions in a cold climate area.Skin symptoms of dryness and rash were alleviated

by both absolute and relative humidity. Alleviationwas slightly more dependent on absolute humidity. Theskin symptoms did not include a denition of the bodypart where the symptoms were felt. Taking intoconsideration that during winter the majority of theskin is covered with clothing, the nding is in agree-ment with the model of Hoppe and Martinac(1998).Our previous results showed that humidicationalleviates skin dryness (Reinikainen et al., 1992).Surprisingly, eye symptoms were not signicantly

associated with either kind of humidity. Our previousresults had shown a decrease in the amount of eyesymptoms when the air was humidied (Reinikainenet al., 1992). According to Carsten and Boge (1993) theoce eye syndrome shows no seasonal variation,which may partly explain the virtual independence ofeye symptoms from humidity in this study population,comprising the workers in the wings of the experimentand a third part of the population whose conditionswere only dependent on natural conditions. On theother hand, neither was there a dependence ontemperature, contrary to the result of Backman andHaghighat (1999) revealing associations between eyesymptoms and temperature rise, as well as pharyngealdryness and eye symptoms.Our previous result showed that humidication does

not signicantly alleviate pharyngeal dryness, and thepresent result, showing a slight decrease when relativehumidity was increased, is in line with this nding(Reinikainen et al., 1992). The result concurs with themodel of Hoppe and Martinac (1998) in that bothhumidity and temperature aect energy loss fromupper airway mucosa, taken that the feeling of drynessis dependent on energy loss. The contradictory (thoughnon-signicant) eects of temperature in humidiedand non-humidied conditions may mirror the energycontent of the humidity.The alleviation of nasal dryness and congestion by

both absolute and relative humidity concurs withHoppe and Martinac (1998), who speculate that thesesymptoms are associated with energy loss frommucosa. Temperature rise seems to increase nasalcongestion. Humidication alone caused no dierencein these symptoms in our previous study, possiblybecause of the higher temperature in the humidied


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conditions (Reinikainen et al., 1992). Sneezingincreased in higher humidity. Thus, while nasal drynessand congestion appeared to act as a single entity,increasing when temperature rose and diminishingwhen humidity rose, sneezing behaved in the oppositemanner.Both absolute and relative humidity increased the

sensation of odor in humidied conditions. By con-trast, in non-humidied conditions, no association waspresent. Higher humidity is not likely to increaseemissions from the building and furnishing materialsother than highly water soluble compounds (Fanget al., 1999). According to the results, humidication isnot associated with odor, as shown in the models ttedwith the humidication variable. Our previous resultsshow an increase in odor sensation when air ishumidied which may be seen to be concordant withthe present result as humidity alone was not assessed inthe previous model (Reinikainen et al., 1992). Thending that the sensation of odor is associated withhumidity is opposite to the results of two chamberstudies where the intensity of odor was found to beindependent of humidity in temperature range 1828Cand 3070% relative humidity. (Fang et al., 1998a,b).We cannot totally exclude the possibility in our studythat some compounds of the humidication water, oremissions from the building or furnishing materialswould have been the cause of an increase in the odorperception in higher humidity. Factors striking againstthis possibility are the nature of the water whichoriginates from a very pure raw water source and is notchlorinated. The ventilation rate, in average 2030 l/sper person is exceptionally high, thus diluting thepossible emissions eectively. We suspect that very lowhumidity conditions may partly cause the insuciencyin odor perception, and a rise in humidity enhances theodor perception ability of the olfactory mucosa.Stuness showed possibly the most interesting

features in this assessment. It was associated withhumidity only if humidication was not included in themodel. We suspect that this phenomenon mirrors thenature of stuness as a sensation of more than onlyodor or sensation in the airways mucosa. The research-ers who visited the building described the feeling duringhumidication as moisture on the skin and a congestivefeeling in the airways. Some of the workers reportedthat during the humidication there was something inthe air resembling a Finnish sauna. The surprisingnding that during non-humidied conditions highertemperature was associated with lower sensation ofstuness may be a consequence of the people opening

their windows because of too high temperature, exces-sive odor, or stuness. That the temperature depend-ence did not appear under humidied conditions maymirror the rather strong stuness-causing eect ofsteam humidication. Our previous results also showedthat the greatest dierence in the individual symptomsand perceptions between humidied and non-humid-ied conditions was in the perception of stuness(Reinikainen et al., 1992). In a report by Berglund andCain (1989), indoor air was perceived as less stuy at alower temperature and humidity. In their study, theincrease in humidity was achieved articially, and thus,it is impossible to evaluate the role of humidicationand humidity separately. On the other hand, a Swedish4-month follow-up study in hospitals, also using steamhumidication, did not show an increase in stunessexperienced in humidied buildings (Nordstrom et al.,1994). Possibly, the contrast between humidied andnon-humidied conditions disappears over a longertime period.

Conclusions

If no humidication is used during the heating seasonwhich in Finland means very low humidity, skin andupper airway symptoms, odor perception, and thesensation of air stuness show no associations with aslight rise in humidity or temperature.Our results suggest that increasing indoor air

humidity during the heating season, to a reasonablelevel, will alleviate skin symptoms and nasal drynessand congestion. The goals can partly be achieved bylowering room temperature alone, which increases therelative humidity, and simultaneously decreases theeects of temperature, which often are opposite to theeects of an increase in humidity. Humidicationemphasizes the alleviating eect of humidity on nasaldryness and congestion, as well as the perception ofodor.Diminishing nasal dryness and skin symptoms may

further be alleviated by increasing indoor air humidity.However, the trade-o of having a less dry andcongested nose, is an increase in sneezing and odorperception. Eye and pharyngeal dryness show noassociation with humidity or temperature. Stunessseems to be increased by articial steam humidication.

Acknowledgements

This study was supported by the Finnish WorkEnvironment Fund.


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significance of humidity and temperature on skin and upper airway symptoms

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