## 1 Introduction  
Oily facial skin may cause skin issues in a large number of people [1]. Typically, the skin appears greasy and dirty, and sebum is overproduced that causes several dermatological complications, including acne and seborrheic dermatitis [2, 3], and also significantly affects the quality of life [4, 5]. There have been a vast variety of oily facial treatments including cosmeceutical products that are easy to broadly use externally [6]. Therefore, controlling oil is an essential key to cosmeceutical product development for these circumstances.  
In the past, skin toner was a typical product used as a second cleansing agent for removing residual makeup after regular facial cleansing or used for removing excess sebum secreted from facial skin to prepare the skin before nourishing treatment. Toners may be categorized into alcohol-based or non-alcohol-based toners for various skin types such as oily skin, sensitive skin, or combination skin [7]. Nowadays, the diversity and prevalence of the products cause skin toners to be utilized more as cosmeceutical products with several purposes; for example, rehydrating skin, balancing skin pH, tightening skin pores, relieving irritation, and also antisepsis. Significantly, because of the growing awareness and demand of natural products, plants have gradually been used much more in cosmeceutical products [8]. Hence, toners that are developed as cosmeceutical products by adding therapeutic benefits of herbal extracts from plant's leaves, twigs, bark, or fruits for controlling oiliness tend to be popular.  
Emblica, _Phyllanthus emblica_ L. is a tree of the family Phyllanthaceae that is native to Southeast Asia and can be found in China and India. It is also called Indian gooseberry. In Thailand, it is known as Ma Kham Pom. The tree is small to moderate, reaching 1-12 m in height, and has 10-20 cm long deciduous branchlets with light green feathery leaves, greenish-yellow flowers, and nearly spherical, light greenish-yellow fruits [9; 10]. Emblica has been used for internal and external applications since ancient times [11; 12]. In addition, emblica is well-known for its high antioxidant content compared to vitamin C [13], which results in a skin whitening effect, and other aesthetic benefits including anti-collagenase and anti-elastase [14]. Moreover, emblica contains several phenolic compounds, including a large amount of tannin [15; 16], which has an stringent effect [17] and an inhibitory effect on 5\(\alpha\)-reductase, abilities that can reduce the skin sebum secretion [18; 19]. The phenolic hydroxyl groups in tannin have an essential role in the asrtingent effect by bringing about protein complexes [20; 21; 22], as a result, plants containing tannin, including apple peel, green tea, and guava leaves, have been studied for their anti-sebum activity [23; 24; 25]. So far, there have been no studies about the clinical efficacy of emblica fruits in terms of anti-sebum activity.  
Therefore, the present research aimed to develop and study the anti-sebum efficacy of toner containing emblica fruit extract (emblica toner) on facial skin in volunteers with oily/combination facial skin using clinical assessment and skin bioengineering measurements.