**2.3 Sound**

The frequency range of audible acoustic sound for adult humans is approximately 20- 16000 Hz (Heffner 2004). However, Oohashi and his coworkers demonstrated that ultrasound at a frequency above 20000 Hz (20 kHz) influences human brain electrical activity and systemic hormonal levels (Oohashi 2000)(Oohashi 2006)(Kawai 2001)(Yagi 2003). Interestingly, these effects did not involve the ear (Oohashi 2006). On the other hand, recent work has demonstrated that a slight, inaudible puff of air on the skin influences auditory perception (Gick & Derrick 2009). These results suggest that an unknown system that is responsive to ultrasound exists at the human body surface. Based on these findings, we considered that audible or inaudible sound frequencies might influence epidermal barrier homeostasis.

First, we evaluated the effects of 5, 10, 20 and 30 kHz sound on intact skin of hairless mice (Denda & Nakatani 2010). We disrupted the permeability barrier by tape stripping and immediately exposed the skin to sound for one hour. The speaker cone lightly touched one side of the flank, and we attached a silent speaker cone to the other flank as a control. Application of sound at a frequency of 10, 20 or 30 kHz accelerated barrier recovery, while 5 kHz sound had no effect. The effects on barrier recovery were observed 23 hours after cessation of the sound application.

To determine whether the effect was induced by sound or skin vibration, we next placed the speaker 1 or 3 cm away from the skin surface. In this case, too, significant acceleration of the barrier recovery by sound was observed. The sound pressure levels were 0 cm: 83 dB, 1 cm: 78 dB, 3 cm: 70 dB.

We also evaluated the effect of different sound pressures on the barrier recovery rate. The sound source was placed 1 cm away from the skin surface, and the frequency was 20 kHz. The barrier recovery rate increased with increasing sound pressure. An electron-microscopic study indicated that exposure to sound at a frequency of 20 kHz accelerated lamellar body secretion between stratum corneum (SC) and stratum granulosum (SG). These results indicate that epidermis might have an unknown system for sensing sound.

#### Fig. 4. Effects of sound on epidermal permeability barrier homeostasis

### **2.4 Electrical potential**

202 Atopic Dermatitis – Disease Etiology and Clinical Management

The frequency range of audible acoustic sound for adult humans is approximately 20- 16000 Hz (Heffner 2004). However, Oohashi and his coworkers demonstrated that ultrasound at a frequency above 20000 Hz (20 kHz) influences human brain electrical activity and systemic hormonal levels (Oohashi 2000)(Oohashi 2006)(Kawai 2001)(Yagi 2003). Interestingly, these effects did not involve the ear (Oohashi 2006). On the other hand, recent work has demonstrated that a slight, inaudible puff of air on the skin influences auditory perception (Gick & Derrick 2009). These results suggest that an unknown system that is responsive to ultrasound exists at the human body surface. Based on these findings, we considered that audible or inaudible sound frequencies might

First, we evaluated the effects of 5, 10, 20 and 30 kHz sound on intact skin of hairless mice (Denda & Nakatani 2010). We disrupted the permeability barrier by tape stripping and immediately exposed the skin to sound for one hour. The speaker cone lightly touched one side of the flank, and we attached a silent speaker cone to the other flank as a control. Application of sound at a frequency of 10, 20 or 30 kHz accelerated barrier recovery, while 5 kHz sound had no effect. The effects on barrier recovery were observed 23 hours after

To determine whether the effect was induced by sound or skin vibration, we next placed the speaker 1 or 3 cm away from the skin surface. In this case, too, significant acceleration of the barrier recovery by sound was observed. The sound pressure levels were 0 cm: 83 dB, 1 cm:

We also evaluated the effect of different sound pressures on the barrier recovery rate. The sound source was placed 1 cm away from the skin surface, and the frequency was 20 kHz. The barrier recovery rate increased with increasing sound pressure. An electron-microscopic study indicated that exposure to sound at a frequency of 20 kHz accelerated lamellar body secretion between stratum corneum (SC) and stratum granulosum (SG). These results

indicate that epidermis might have an unknown system for sensing sound.

Fig. 4. Effects of sound on epidermal permeability barrier homeostasis

**2.3 Sound** 

influence epidermal barrier homeostasis.

cessation of the sound application.

78 dB, 3 cm: 70 dB.

It has been demonstrated that cultured human keratinocytes migrate to the negative pole in direct current electrical fields (Nishimura 1996). This result suggested that keratinocytes might have a sensory system for the external electrical field. Thus, we hypothesized that external electrical potential would influence epidermal barrier homeostasis. We applied negative and positive direct electric potential (0.5 V) to hairless mouse flank skin immediately after barrier disruption for one hour, and then we evaluated barrier recovery by the measurement of transepidermal water loss. At the area of applied negative potential, the barrier recovery rate was significantly accelerated, while the recovery was delayed at the area of positive applied potential (Denda & Kumazawa 2002).

We subsequently found that several interfacial electrical conditions also affect barrier homeostasis. For example, topical application of barium sulfate or aqueous solution of ionic polymers formed an electrical double layer on the skin surface and affected the barrier recovery rate (Fuziwara 2004)(Denda 2005). Moreover, just placing metals on the skin surface after barrier disruption accelerated the barrier recovery, presumably because free electrons were supplied from metal to the skin surface (Denda & Kumazawa 2010). When chemically different materials are in contact, electro-chemical phenomena, such as formation of an electrical double layer, are induced. We previously demonstrated that a voltage-gated calcium channel is expressed at the upper layer of the epidermis (Denda 2006). Thus, when the skin touches other materials, physiological phenomena might be induced.
