The Effect of Ultra Fine Bubbles Water on the Human Skin
Authors: Kato Yuji , Matsumoto Tomoyuki , Koura Setsuko 
Published: December 2020

1. Introduction
Skin barrier function refers to a role of preventing evaporation of moisture from the body and a role of protecting the body from invasion and irritation of foreign matter from the outside. In order to maintain this function, a certain amount of water must be retained in the stratum corneum of the skin, so it is necessary to supply water to the stratum corneum of the skin and prevent evaporation. Lotions and moisturizers are commonly used as countermeasures. However, the preservatives and surfactants contained therein have an adverse effect on children with weak skin, elderly people, patients with atopic predisposition, etc., such as inducing skin dryness and inflammation. Therefore, methods for improving the skin barrier function that have little effect on the human body are being studied.
Ultra-fine bubbles (UFB) refers to bubbles having a diameter of 1㎛ or less, has a lower floating speed in water than ordinary bubbles, and has a property of target gas in water for a long time. It is also said that bubbling at the time of UFB water production subdivide water clusters and lowers surface tension1). Since ordinary water has a large cluster, it is difficult to penetrate into the stratum corneum of the skin. Therefore, we thought that the use of UFB water with a small water cluster would facilitate penetration into the stratum corneum of the skin and help to improve the skin barrier function that is kind of the body.
In this paper, we evaluated the effects of UFB water on the human skin.
2. Experimental
2.1 Generation of oxygen UFB water
UFB water was prepared by gas-liquid mixed shear method with compact generator (Sunstar Inc.). In this equipment, UFB water was produced under the conditions of gas flow rate of 0.45 L/min, number of revolutions 4000 rpm, operating time 10 min, and amount of pure water 1 L. The kinds of gas selected were oxygen, air, nitrogen and argon.
The dissolved oxygen (DO) concentration in the water was measured by DO meter of Thermo Fisher Scientific Co. The meter can measure the DO concentration 0 to 50mg/L. Size distribution of oxygen UFB was measured by laser scattering Nano-Sight LM10-HFV (Malvarn Panalytical).
2.2 Evaluation of the effect of UFB water on skin model
The skin model used was Human three-dimensional cultured epidermis LabCyte EPI-MODEL24 (Japan Tissue Engineering Co., Ltd.). Pure water and UFB water containing each gas were dropped on the skin model, and the water content and transepidermal water loss (TEWL) before and after dropping were compared respectively.
2.3 Evaluation of contact angle of UFB to the human skin
Tape stripping was performed on the inside of the subject’s forearm. Then, the skin collected by tape stripping was used as a substrate, and pure water and UFB water containing each gas were dropped respectively thereon to generate droplets. Thereafter, the affinity of each solution to the skin was compared by measuring the contact angle of droplet using a contact angle meter DM300 (Kyowa Interface Science Co., Ltd.).
3. Results and Discussion
The results of water content value for the skin model with each water showed the highest water content in the case of oxygen UFB water. And also, we found the lowest TEWL with oxygen UFB water. These results suggested that oxygen UFB water has an effect of improving the skin barrier function.
From the contact angle measurement, we could find the smallest value with oxygen UFB water on the skin. In addition, the contact angle with air UFB water produced by supplying air instead of oxygen was not different from that of pure water. These results show that the affinity with the skin is not increased by the subdivision of the water cluster by bubbling, but that the higher the concentration of oxygen UFB, the higher the affinity with the skin.
Zeta potential of oxygen UFB showed negative charge. In addition, it has been reported that anionic substances easily penetrate the skin2). Therefore, it was suggested that oxygen UFB water has a high affinity for the skin and has an effect of improving the skin barrier function.
References
1) Shozo Himuro, A New Washing Method Using Microbubbles, Progress in multiphase flow research, 2, 39-45 (2001).
2) Onseok Lee, Influence of surface charge of gold nanorods on skin penetration, Skin research and technology, 19 (2012).