**5. Application of hydrophobic extract of licorice for cosmetics and foods**

Recently, the species‐specific flavonoids from hydrophobic extracts of *G. uralensis, G. glabra*, and *G. inflata* were found. The primary active ingredient isolated from *G. uralensis* was glycycoumarin, that isolated from *G. glabra* was glabridin, and that isolated from *G. inflata* was licochalcone A (**Figure 1**). In the course of our studies on the further application of licorice as a cosmetic ingredient, we studied new dermatological availabilities in the hydrophobic extracts of licorice containing licochalcone A isolated from *G. inflata* and glabridin isolated from *G. glabra*.

#### **5.1. Efficacies of hydrophobic extract from** *G. inflata* **(HPGI)**

The primary active ingredient isolated and extracted from *G. inflata* is licochalcone A, an oxygenated retrochalcone that exhibits antimicrobial, antioxidative, anti‐inflammatory, antiparasitic activity, and antitumorigenic activity [12, 13].

We indicate several efficacies of hydrophobic extracts from *G. inflata* (HPGI), especially in dermatological uses. The efficacy of HPGI against sebum‐induced skin trouble was assessed in several experiments (**Table 4**) [14]. An androgenic hormone, testosterone, is converted into a pharmacologically active compound, dihydrotestosterone, by an intracellular enzyme, testosterone 5α‐reductase. Dihydrotestosterone combines with the androgen receptor of the sebaceous gland to increase the sebum. Ultimately, the increase of sebum‐secretion promotes skin trouble through the oxidative damage and increase of acne fungus.


**Table 4.** Inhibitory effects of HPGI on sebum‐induced skin trouble experiments.

(1) Inhibitory test of testosterone 5α‐reductase. As shown in **Table 4**, in an assay of the inhibitory effect against testosterone 5α‐reductase activity, HPGI demonstrated the potent inhibitory activity. The inhibitory ability was more effective than positive controls (ethynyl estradiol (IC50: 31.5 ppm) and benzyl peroxide (IC50: 129 ppm)).

(2) Inhibitory effect against androgen receptor.

In this assay, HPGI inhibited the binding of dihydrotestosterone on the receptor at a low concentration and its IC50 was 5.8 ppm (**Table 4**). From this result, it was indicated that HPGI has a binding ability in the androgen receptor and works an androgen antagonist.

(3) Inhibitory effect against lipase and phospholipase A2.

HPGI indicated the inhibition of lipase (IC50: 43.6 ppm) and phospholipase A2 (IC50: 0.38 ppm). In this case, the potency of HPGI against phospholipase A2 was remarkable.

(4) Superoxide dismutase (SOD) like activity.

The suppressant effect of HPGI on active oxygen generation was examined by the reduction of nitro blue tetrazolium (NBT) in a xanthine‐xanthine oxidase system. In this assay, HPGI suppressed the generation of active oxygen at low concentration (IC50: 7.0 ppm).

(5) Antimicrobial activity against *Propionibacterium acnes*.

In the hair follicle and the sebaceous gland, *P. acnes* produces the chemotactic factor that enhances the migration of neutrophils toward the hair follicle or the sebaceous gland, and causes the development of acne. In addition, *P. acnes* is considered to increase the release of cytokine and T‐lymphocyte. These cells and the sebaceous gland also promote damage by acne through allergic reaction. Furthermore, *P. acnes* can multiply in the hair follicle by using the sebum as a nutriment and enhance the production of enzyme, such as lipase, protease, and hyaluronidase. Among these enzymes, lipase attacks sebum to give free fatty acid and promotes the formation of the primary eruption, comedo. Besides, free radicals generated from fatty acid attack phospholipid in cell membranes result in the formation of chemical mediators, such as prostaglandins and leukotrienes. These mediators derived by the action of phospho‐ lipase A2 enhance the development of acne through inflammatory reaction.

HPGI has antimicrobial activity against *P. acnes* at a low concentration (MIC: 31.3 ppm).

(6) Efficacy assessment in acne patient.

in several experiments (**Table 4**) [14]. An androgenic hormone, testosterone, is converted into a pharmacologically active compound, dihydrotestosterone, by an intracellular enzyme, testosterone 5α‐reductase. Dihydrotestosterone combines with the androgen receptor of the sebaceous gland to increase the sebum. Ultimately, the increase of sebum‐secretion promotes

(1) Inhibitory test of testosterone 5α‐reductase. As shown in **Table 4**, in an assay of the inhibitory effect against testosterone 5α‐reductase activity, HPGI demonstrated the potent inhibitory activity. The inhibitory ability was more effective than positive controls (ethynyl

In this assay, HPGI inhibited the binding of dihydrotestosterone on the receptor at a low concentration and its IC50 was 5.8 ppm (**Table 4**). From this result, it was indicated that HPGI

HPGI indicated the inhibition of lipase (IC50: 43.6 ppm) and phospholipase A2 (IC50: 0.38 ppm).

The suppressant effect of HPGI on active oxygen generation was examined by the reduction of nitro blue tetrazolium (NBT) in a xanthine‐xanthine oxidase system. In this assay, HPGI

In the hair follicle and the sebaceous gland, *P. acnes* produces the chemotactic factor that enhances the migration of neutrophils toward the hair follicle or the sebaceous gland, and causes the development of acne. In addition, *P. acnes* is considered to increase the release of cytokine and T‐lymphocyte. These cells and the sebaceous gland also promote damage by acne through allergic reaction. Furthermore, *P. acnes* can multiply in the hair follicle by using the sebum as a nutriment and enhance the production of enzyme, such as lipase, protease, and

has a binding ability in the androgen receptor and works an androgen antagonist.

In this case, the potency of HPGI against phospholipase A2 was remarkable.

suppressed the generation of active oxygen at low concentration (IC50: 7.0 ppm).

skin trouble through the oxidative damage and increase of acne fungus.

**Tests Inhibitory effect (IC50: ppm)**

Testosterone 5α‐reductase activity 18.7 Androgen receptor 5.8 Lipase activity 43.6 Phospholipase A activity 0.38 SOD‐like activity 7.0

18 Biological Activities and Action Mechanisms of Licorice Ingredients

Antimicrobial activity against *P. acnes* 15.6 (MIC)

**Table 4.** Inhibitory effects of HPGI on sebum‐induced skin trouble experiments.

estradiol (IC50: 31.5 ppm) and benzyl peroxide (IC50: 129 ppm)).

(3) Inhibitory effect against lipase and phospholipase A2.

(5) Antimicrobial activity against *Propionibacterium acnes*.

(2) Inhibitory effect against androgen receptor.

(4) Superoxide dismutase (SOD) like activity.

From the above‐mentioned results *in vitro* assays, HPGI expected following four actions: (1) inhibitory action of sebum production, (2) antimicrobial action, (3) inhibitory action of allergic and inflammatory response, and (4) suppressant action of oxidative damage.

Therefore, we assessed the efficacy of HPGI in acne patients.

Twenty female acne patients received anti‐acne gel containing HPGI. All patients applied anti‐ acne gel onto the whole face twice or three times daily for 2 weeks.

**Table 5** shows the result of efficacy assessment in acne patients. In 17 of the 20 patients tested, the improvement effect was recognized [13].


**Table 5.** Result of efficacy assessment of HPGI preparation in acne patients (*n* = 20).

**Figure 3.** Structure of flavonoid in HPGG.
