Table 3.

Possible sensor integration on the masks.

Sensors and features						Applications
Location: mask main body
	Type: biosignal information
		Source: breath (respiration)
			Pressure sensor
				Respiration rate or volume	Personal health or sport [27,28]
			Chemical sensor
				Ketone: acetone	Personal health or disease (diabetes) [41-43]
				Hydrogen sulfide	Personal health [44,45]
				Toluene	Personal health or disease (lung cancer) [46-48]
		Source: facial blood vessels
			Photoplethysmography sensor
				Heart rate variability	Physical health or mental health [49-51]
				Oxygen saturation	Physical stress [31,49]
				Blood pressure	Hypertension or hypotension [51-53]
		Source: skin
			Electrooculography sensor
				Eye blink	Concentration [54,55]
			Electrodermal activity sensor
				Electrodermal response	Emotion [56,57]
			Temperature sensor
				Temperature change	Communicable diseases [25,26,31,32]
			Electromyography sensor
				Facial muscle	Emotion [55,59]
				Facial muscle	Pain [60]
		Source: head
			Inertial measurement unit
				Motion	Posture [61]
	Type: environmental information
		Source: air
			Chemical sensor
				Environment air quality	Local air quality [22,39]
		Source: external temperature
			Thermometer
				Temperature	Local temperature [62]
		Source: external humidity
			Humidity sensor
				Humidity	Local humidity [63-65]
Location: mask support frame
	Type: biosignal information
		Source: ear
			Electroencephalography sensor
				Brain activity	Drowsiness or fatigue [66]
		Source: neck
			Inertial measurement unit sensor
				Motion	Posture [61]
			Electrocardiographic sensor
				Heart	Heart disease [67,68]