Topical Applications of Bakuchiol: An Emerging Cosmeceutical

The use of topical retinoids has proven effective in addressing a range of prevalent skin issues, such as skin aging, acne, and the treatment of hyperpigmentation. A frequent challenge in using topical retinoids, including over-the-counter forms, is the short-term experience of cutaneous side effects such as pruritis, erythema, peeling, xerosis, and stinging or burning sensations. ^1,2  Such a tolerability issue can further challenge patient compliance. In an ideal situation, we would obtain the benefits of retinoids without such side effects. An emerging cosmeceutical ingredient seems to be accomplishing such a feat, at least to a minor degree. This article will explore the research surrounding the topical use of bakuchiol, a plant-derived phenol, for use in skin aging (particularly by those experiencing skin sensitivities), acne vulgaris, and postinflammatory hyperpigmentation.

Bakuchiol: A Brief Review

Although it is found in various plants, the purified meroterpene phenol of bakuchiol is mainly sourced from the seed of Psoralea corylifolia. ³ This plant retains a rich history within both Chinese and Indian traditional medical systems. ^4,5 Bakuchiol has demonstrated numerous biological activities including as an anti-inflammatory, antioxidant, antibacterial, antitumor, and antiacne. ^6,7,8 Most clinical trials have used bakuchiol in topical concentrations between 0.5% and 1.0% and have reported it to be well-tolerated. ⁹ It is also essential to ensure that a given topical formulation is utilizing the purified isolate of bakuchiol rather than a whole plant extract or bakuchi oil form, as these less pure forms may contain phototoxic compounds like psoralens, which can increase photosensitivity and adverse effects when used topically. ¹⁰

Evidence for Use in Skin Aging and Skin Sensitivity

Central to mitigating against the appearance of fine lines and wrinkles is the notion of bakuchiol functioning as a retinol analog, despite the two compounds having no structural resemblance.^11,12 Several research methodologies have been employed to support this theory; these include examining the resemblance between bakuchiol and retinol in terms of gene expression profiles in a full-thickness skin substitute model, ^13,14 modulating specific genes associated with extracellular matrix and dermo-epidermal junction components, and assessing collagen stimulatory effects in human fibroblasts using ELISA-based evaluation.^15,16 Beyond these effects, bakuchiol’s antioxidant and anti-inflammatory properties are also believed to contribute toward its effects on skin aging. Specifically, a research team has described notable antioxidative capacity and power (which quantifies both capacity and reactivity) for bakuchiol using methods such as electron spin resonance spectrometer.¹⁷ As for limiting the inflammatory response, the same team also demonstrated, in separate in vitro studies using human dermal fibroblasts, a reduction in both prostaglandin E₂ (PGE₂) and macrophage migration inhibitory factor (MIF) levels. Both have been implicated in skin-aging mechanisms. ¹⁸

Research and Review Snapshot  ¹⁹

A systematic review exploring and summarizing the application of bakuchiol for various dermatologic concerns was recently published; the bulk of the studies meeting inclusion criteria were directed toward the use of bakuchiol for skin aging. This included three preclinical and six clinical trials. Overall, although the authors expressed a need for further studies to explore the use of bakuchiol more fully in skin care, they highlighted how clinical studies have generally demonstrated bakuchiol to be effective in comparison to retinol. In in vivo studies, bakuchiol was administered either independently or in conjunction with other products, leading to a notable decrease in photodamage, hyperpigmentation, wrinkle scores, and the severity of acne. The review additionally highlighted how bakuchiol offers those with sensitive skin a more tolerable option for managing the signs of skin aging.

Research and Review Snapshot ²⁰

One example of the clinical trials described in the above-mentioned systematic review was a a 12‑week randomized controlled trial (RCT) with 44 participants, predominantly females, conducted under double-blind conditions. Half of the participants applied 0.5% retinol to the full face once nightly, while the second group applied 0.5% bakuchiol cream to the full face twice daily. Evaluations included a computer-based facial-image analysis for skin wrinkling, erythema, and pigmentation; dermatologist grading for pigmentation, scaling, and erythema; and a participant-graded tolerability scale. Notable findings reaching statistical significance included the following:

• As compared to baseline, both retinol and bakuchiol demonstrated a reduction in the surface area involvement of fine wrinkles on the face by the 12‑week mark (p < 0.05). In this finding, no significant difference was found between retinol and bakuchiol.
• As compared to baseline, both retinol and bakuchiol demonstrated a reduction in both the surface area involvement of pigmentation on the face (both p < 0.05) as well as pigmentation intensity by the 12‑week mark (p < 0.05 for retinol, p = 0.05 for bakuchiol). No significant difference was found between retinol and bakuchiol in the computer-based imaging analysis or dermatologist grading.
• At all evaluation points (4, 8, and 12 weeks), dermatologist-assessed scaling was significantly higher in the retinol group as compared to the bakuchiol group (p < 0.05). The retinol group also reported more stinging at week 4 (p < 0.05), which reduced as the study proceeded.

Research and Review Snapshot²¹

A noted benefit of bakuchiol is its ability to offer retinol-like effects for skin aging without the same degree of tolerability issues. This uniquely positions bakuchiol as a potential option for managing photoaging in patients with sensitive skin. In a 4‑week trial, 60 female participants (40–65 years old; Fitzpatrick skin types I–V) with self-perceived skin sensitivity and mild-to-moderate signs of photodamage (specifically skin wrinkles and uneven skin tone) were assigned a skin cleanser and 1% bakuchiol-based moisturizer, each applied twice daily over the face and neck. Notable findings reaching statistical significance from baseline measures included the following:

• Improvements in investigator-rated parameters such as visual smoothness, tactile smoothness, global antiaging, and overall appearance (p < 0.001).
• A 16% increase in skin hydration as measured by corneometry (p < 0.001), a technique used in dermatology and skincare to measure the hydration levels of the skin’s outermost layer, known as the stratum corneum.
• No change to transepidermal water loss, signifying how these subjects likely experienced no skin-barrier damage and/or did not experience any worsening of their skin barrier integrity.
• Overall, subject-rated tolerability assessment demonstrated how the formula was very well tolerated. No tolerability concerns were found on investigator assessment. Through the fourth week, 10% of subjects indicated minimal stinging (p = 0.031), and minimal tightness was reported by a few others (p = 0.017).

Evidence for Use in Acne Vulgaris

A variety of preliminary in vitro work has suggested a potential role for bakuchiol in the management of acne vulgaris. If these effects are confirmed, they once again demonstrate how bakuchiol’s impact on a given skin concern can be multifactorial. These include downregulation of 5‑α‑reductase; antibacterial and antifungal activities, including against Cutibacterium acnes; anti-inflammatory activity, including inhibition of cyclooxygenase; inhibition of both collagenase and elastase activity, which may help limit subsequent acne-scar development; as well as the reduction of oxidative stress, particularly the inhibition of lipid peroxidation. ^22,23

Research and Review Snapshot²⁴

A pilot clinical trial was performed by a team employed for a bakuchiol manufacturer. While no statistical analysis of study results were reported, the trial, however, does provide an interesting picture regarding the use of bakuchiol, both on its own and in combination with salicylic acid, a popular beta‑hydroxy acid exfoliant used to dislodge the comedonal plug from its follicular lining. Sixty (60) volunteers with mild-to-severe acne were assigned to one of four treatment groups, which corresponded to lotions containing 1% bakuchiol, 2% salicylic acid, 1% bakuchiol and 2% salicylic acid, and control. In this 6‑week trial, the lotions were applied twice daily over the full face. The Global Acne Grading System was used to determine the percent reduction in acne from baseline values determined by dermatologist examination.

Notable findings at the 6‑week mark for acne grading included:

• A 57% reduction in the bakuchiol-only group;
• A 48% reduction in the 2% salicylic acid–only group;
• A 67% reduction in the combination group; and
• A 11% reduction in the control group.

No subjects reported, or were observed to experience, any adverse reaction with any of the lotions used.

Although additional study is needed, this pilot trial suggests how bakuchiol, both as a solitary agent and especially when combined with salicylic acid, may provide an effective treatment for acne vulgaris.

Evidence for Use in Hyperpigmentation

Bakuchiol has drawn interest for skin-lightening effects in relation to mitigating hyperpigmentation. This is built upon various lines of evidence, such as in vitro work using a melanoma cell line, which demonstrated a potent inhibition of melanin production for bakuchiol over arbutin, another popular agent of depigmentation. ²⁵ Interestingly, preliminary clinical studies exploring bakuchiol’s effects in this way come from acne studies which concurrently explored effects on postinflammatory hyperpigmentation (PIH) development over areas of previously acne lesions. In addition to the study described below, a systematic review reported on such studies, together suggesting an ability for bakuchiol to improve PIH.²⁶

Research and Review Snapshot ²⁷

A prospective, nonrandomized trial took a novel approach in studying the effects of bakuchiol on PIH. Here, 20 subjects of skin types IV–VI with facial acne and a history of acne-induced PIH, also had three PIH lesions induced using trichloroacetic acid (TCA) over an area on the buttock. After three facial acne lesions transitioned into PIH, the subjects applied, in a blind fashion, bakuchiol-containing cream and vehicle cream to the respectively assigned acne and TCA‑induced PIH lesions, with one set of lesions left untreated as a control; this was done twice daily for 28 days. Investigator’s global assessment (IGA) scoring for hyperpigmentation served as the outcome measure. Notable findings included:

• IGA scores for bakuchiol-treated, TCA‑induced PIH showed a significantly greater improvement (−0.50 ± 0.18) as compared to vehicle-treated (0.05 ± 0.15) and control (−0.06 ± 0.17) (p < 0.05).
• IGA scores for bakuchiol-treated, acne-induced PIH also demonstrated notable improvement (−1.06 ± 0.23) as compared to vehicle-treated (−0.56 ± 0.16) and control (−0.69 ± 0.18); however, this finding failed to reach statistical significance (p > 0.05).

The authors postulated how the above findings may have been influenced by the challenge in finding facial acne–induced PIH lesions which, at baseline, are uniform in size and intensity as compared to the PIH resulting from TCA induction. Longer follow-up was also recommended for future studies.

Although still relatively recent since its emergence in topical formulations, research to date suggests bakuchiol is quickly finding a place within the realm of agents offering notable dermatological effects. From mitigating against photoaging, especially in those with sensitive skin, to managing acne and its sequelae of hyperpigmentation, it will be exciting to see what further findings are established for this novel cosmeceutical.

Disclaimer: The information presented in this article is for general information purposes only and does not constitute medical advice. Please first review with your personal health-care practitioner(s) what therapeutic approaches and products would be best for your case.