Introduction: 

Ursolic acid, a carboxylic acid present in a wide variety of plants in the form of a free acid or an aglycone of triterpene saponins.It is also known as urson, prunol, micromerol, and malol, is a pentacyclic triterpenoid compound which naturally occurs in a large number of vegetarian foods, medicinal herbs, and plants1,2. For a long time, it was considered to be pharmacologically inactive3. Thus, ursolic acid and its alkali salts (e.g. potassium or sodium ursolates) were exclusively used as emulsifying agents in pharmaceutical, cosmetic, and food preparations3,4. However, upon closer examination, ursolic acid was found to be medicinally active both topically and internally1. Its anti-inflammatory, antitumor (skin cancer), and antimicrobial properties make it useful in cosmetic applications1. 

Ursolic acid, also known as urson, prunol, micromerol, and malol, is a pentacyclic triterpenoid compound which naturally occurs in a large number of vegetarian foods, medicinal herbs, and other plants1,2. For a long time, it was considered to be pharmacologically inactive3. Thus, ursolic acid and its alkali salts (e.g. potassium or sodium ursolates) were exclusively used as emulsifying agents in pharmaceutical, cosmetic, and food preparations3,4. However, upon closer examination, ursolic acid was found to be medicinally active both topically and internally1. Its anti-inflammatory, anti-tumor (skin cancer), and antimicrobial properties make it useful in cosmetic applications1.    

Notwithstanding its numerous cosmetic properties, ursolic acid is an ideal cosmetic ingredient because its overall toxicity (both chronic and acute) is low. It is not a primary irritant or sensitizer. In fact, it has been termed dermatologically innocuous4. 

Uses: 

1.  Pharmacological Action: 

Medicinal plants containing ursolic acid have been used in folk medicine before it was known which constituents were responsible for their therapeutic effectiveness. Contemporary scientific research which led to the isolation and identification of ursolic acid revealed and confirmed that several pharmacological effects, such as, anti-tumor, hepatoprotective, anti-inflammatory (oral and topical), anti-ulcer, antimicrobial, anti-hyperlipidemic and antiviral, can be attributed to ursolic acid1.

However, its anti-inflammatory (topical), anti-tumor (skin cancer), and antimicrobial properties are pertinent to the cosmetic industry. 

2.      Anti-aging agent:  

Ursolic acid treatment improves the health of skin and hair. Ursolic acid and its derivatives form oil-resistant barriers on the skin and hair as they do in the waxy coating of fruits6. Ursolic acid has been used to treat photoaged skin because it prevents and improves the appearance of wrinkles and age spots by restoring the skin's collagen bundle structures and its elasticity31. Concentrations of ursolic acid ranging from 0.01 to 50 mg have been reported for inclusion in skin treatment preparations 32-33. 

3.  Hair growth stimulant: 

Ursolic acid and its isomer, oleanolic acid, have been used in to nics to enhance hair growth and prevent scalp irritation26,27. Both triterpenoid compounds encourage hair growth by stimulating the peripheral blood flow in the scalp and activating the hair mother cells. They also furnish alopecia-preventing and dandruff-preventing effects27. 

4.  Antimicrobial activity: 

β ursolic acid (triterpenoid sapogenin from the ursan group) inhibited the growth of several strains of staphylococci28. Numerous ursolic acid containing plants from the Lamiaceae family exhibited antibacterial/ fungal activity29. The minimal inhibitory concentration of Rosmarinus officinalis, Origanum majorana, and Lavandula officinalis were 500, 250, and 500 mg/cm3, respectively29. Ursolic acid also inhibited the growth of Microsporium lenosum and Candida albicans at 250 mg/mL30. 

5.      Anti-inflammatory activity: 

Ursolic acid is a potent anti-inflammatory agent. Thus, it has been recommended for use in burn ointments4. It not only inhibits human leucocyte elastase(HLE), but also 5-lipoxygenase and cyclooxygenase activity21, 22. Ursolic acid (1.0 mg/ear) inhibited TPA-induced mouse ear edema by 72.4%23. Hirota and coworkers24 determined that 200 mg and 50 mg applications of ursolic acid inhibited 12-O-hexadecanoyl-16-hydroxyphorbol-13-acetate (HPPA) - induced inflammation by 49% and 33%, respectively. In addition, it inhibited concanavalin A (Con A) induced histamine release, which can cause severe inflammation, by 95% at a concentration of 0.001 M25. 

6.      Inhibition of tumor promotion in skin:

Ursolic acid (UA) and oleanolic acid (OA), isolated from Glechoma hederacea, inhibited Epstein-Barr virus activation induced by 12-O-tetradecanoylphorbol 13-acetate (TPA) in mouse skin. The inhibitory effects were evaluated for 20 weeks. Continuous application of UA and OA (41 nmol of each) before TPA-treatment (4.1 nmol) delayed the formation of papillomas in mouse skin and reduced the rate (%) of papilloma bearing mice. Both UA and OA exhibited remarkable inhibitory activity against tumor promotion, which is comparable to the known tumor inhibitor, retinoic acid (RA). Compared to either RA or OA, ursolic acid inhibited tumor more effectively after a single application before initial TPA-treatment as shown in Figure 1. This suggests that the role of tumor inhibition by UA differs from that of either RA or OA. It is suggested that pretreatment of skin with UA may inhibit the first dramatic cellular event in tumor promotion caused by TPA^17. 

Topical application of ursolic acid derived from rosemary extract inhibited TPA-induced tumor initiation and promotion, inflammation, and ornithine decarboxylase activity in mouse skin. Ursolic acid exhibited strong anti-inflammatory activity. It is even more active than of 1 or 2 mmol of ursolic acid along with 5 nmol of TPA for TPA for 20 weeks inhibited the formation of skin tumors per mouse by 45 or 61% respectively.

Lower doses (0.1 or 0.3 mmol) of ursolic acid had a similar inhibitory effect as the higher doses. Twice weekly topical application of 0.1, 0.3, 1, or 2 mmol of ursolic acid along with 5 nmol TPA for 8,12, and 18 weeks reduced the number of skin tumors per mouse by 52-86%, 49-63%, and 44-61%, respectively18.

Ursolic acid and its isomer, oleanolic acid have been recommended for skin cancer therapy in Japan19. Topical cosmetic preparations containing ursolic acid/ oleanolic acid have been patented in Japan for the prevention of topical skin cancer20. An ursolic acid/ oleanolic acid ointment inhibited 7,12-dimethylbenz [a] anthracene (DMBA)-induced skin cancer in mice. Reportedly, 0% and 3% of mice developed cancer in 15 weeks and 30 weeks, respectively compared to 50% and 90% for the control mice20. 

Botanical Sources: 

Like most triterpenoids, ursolic acid is ubiquitous in the plant kingdom5. Ursolic acid and its derivatives are constituents of numerous plants which are having diversified phylogenetic origin and taxonomic position. It has been isolated from the protective wax-like coatings of apples, pears, cranberries, prunes, and other fruits6. Seaweed’s are rich in ursolic acid derivatives6. Some of the more commonly known medicinal plants containing ursolic acid are shown in Table 16,7. 

Table 1. Partial List of Medicinal Plants Containing Ursolic Acid