Hair are instrumental in enhancing the facial features and overall appearance of both men and women And shampoos serve as indispensable cosmetic products that primarily maintain scalp health and the aesthetic quality of hair. The shampoo removes dirt and unwanted lipophilic substances, especially sebum and perspiration to clean the scalp and hair(Al Badi and Khan 2014; Gubitosa et al. 2019). Based on the source of the active ingredients, shampoos could be broadly categorized as synthetic and herbal or botanical. Chemicals are the active components in synthetic shampoos that offer targeted treatments like anti-dandruff, deep cleansing, volumizing or smoothing. These shampoos provide consistent and quick results, however, active chemicals in these shampoos are harsh, and hazardous that can strip natural oils and potentially may even cause irreversible adverse effects with prolonged use(Trüeb 2007). On the contrary, herbal shampoos are formulated using plant ingredients with limited surfactants, active chemicals and preservatives are perceived as safer but less effective(Mainkar and Jolly 2000; Al Badi and Khan 2014). They are considered gentle because of either absence or lower concentrations of active ingredients and chemicals. Dandruff is a condition that ruins the scalp health and causes irritation, itching, scalp skin flaking and most importantly impacts self-consciousness. For quick and immediate effects synthetic shampoos are preferred over herbal shampoos considering the latter less effective. Interestingly, there are only a few studies that are directly comparing the effectiveness of herbal and synthetic shampoos(Al Badi and Khan 2014). The current study, therefore, assessed the effectiveness of herbal and synthetic shampoos in combating the growth and viability of M. furfur, the primary fungus responsible for dandruff. Previous research findings have very well established the implication of M. furfur in causing dandruff. Preventing and inhibiting the growth of M. furfur is prerequisite for controlling dandruff. We selected three synthetic shampoos with varying compositions and three plant-based shampoos. Ketoconazole containing (KETO) shampoo was considered as a comparator of antifungal activity for the herbal and synthetic shampoos.

The experiments were planned with diluted shampoos as low as 1% and comparing their respective zones of inhibition created on M. furfur growth. All the shampoos showed a dose-dependent effect, however, at lower dilutions up to 10%, all three herbal shampoos demonstrated inhibitory zones similar to the synthetic shampoos, except, SYN_01 (Fig. 1). We performed comparative analysis at suboptimal doses to identify variations in anti-furfurative potency among shampoos (Fig. 2). Higher concentrations might result in pronounced fungal inhibition under in vitro settings, which can obscure differences in efficacy between shampoos. This study employs a unique set of experiments, designed to replicate real-life conditions. Considering the brief exposure of the scalp and hair to diluted shampoos, we conducted contact experiments in which M. furfur momentarily interacted with various shampoos. This approach is pivotal for evaluating the rapid antifungal efficacy of shampoos against M. furfur. Our findings demonstrate that even brief exposure to both herbal and synthetic shampoos significantly reduced yeast viability, providing practical insights into the immediate antifungal effects and real-world efficacy of anti-dandruff shampoos (Fig. 3). In these experiments, we determined, that herbal shampoos are no less effective than synthetic shampoos. However, SYN_01 and KETO showed highest efficacy. Following a brief exposure to shampoo, M. furfur was allowed to recover for 24 h in growth media to simulate real-life conditions. This experimental approach mimics the scenario in which yeast cells on the scalp encounter short shampoo exposures but then recover in the skin habitat until the next shampoo application. Experimentally, we determined that M. furfur was able to gradually recover within 72 h after shampoo exposure in all shampoos. Interestingly, at 1% all shampoos had similar effects. It is at 5%, where we observed SYN_01 was as efficient as comparator, KETO. Herbal and two other synthetic shampoos had similar effects on growth and viability, wherein M. furfur recovered to the normal growth pattern within 72 h of shampoo exposure. Based on these findings, an experiment was designed to expose M. furfur to shampoos daily, thereby simulating a real-life scenario of daily scalp and hair cleansing. Additionally, the experiment compared the fungicidal effect of once every three days versus daily scalp cleansing. M. furfur when exposed to shampoos every day showed no visible recovery in growth and viability. All the shampoos demonstrated fungicidal effects even at 1% dilution. Notably, the experiment also highlighted that herbal shampoos exhibit efficacy comparable to synthetic shampoos (Fig. 4). Collectively, in most of the experiments, SYN_01 showed robust antifungal activity compared to other synthetic and herbal counterparts. Hence, we thoroughly studied the ingredients present in all shampoo types (Supplementary Table 1). Herbs like Aloe barbadensis, Lawsonia inermis, Azadirachta indica, Ocimum sanctum and Emblica officinalis were common components in all herbal shampoos used in the study. These herbs have been scientifically tested for antimicrobial effects and are known to promote hair growth since ancient times. This study aimed to address beliefs that herbal shampoos are less effective compared to synthetic, however are less harmful. We demonstrate herbal shampoos are as effective as synthetic shampoos even at dilutions of 1% through various unique experiments reflecting real-life situations. The tabular comparison of presence of preservatives, surfactants and allergens would address the potential health hazards linked with shampoos (Table 1). Maximum number of surfactants were listed in SYN_01 comprising of sodium lauryl sulfate, considered effective but harsher compared to Sodium Laureth Sulfate (SLES). Surfactants are primary scalp cleansers in shampoos that remove the unwanted lipophilic substances that provide favourable habitat on the scalp for yeasts like M. furfur(Draelos 2010). Other surfactants like, cocamidopropyl betaine and cocamide MEA, both are coconut oil derivatives and mild surfactants present in the herbal shampoos and other synthetic shampoos, namely, SYN_02 and SYN_03(Draelos 2010). Preservatives, active ingredients or other category of chemicals used in shampoos could be potential allergens. We therefore compared all the allergens present in shampoos that may or may not be listed under Regulation (EC) No. 1223/2009(Cosmetic Commission Regulation (EU) 2016/1198 of 22 July 2016 amending Annex V to Regulation (EC) No.; Regulation (EC) No. 1223/2009 of the European Parliament and of the Council of 30 November 2009 on cosmetic products). We would like to highlight that herbal shampoos do not contain allergens; on the contrary synthetic shampoos contain a wide range of allergens like methylisothiazolinone and methylchloroisothiazolinone and DMDM hydantoin are the allergens listed under Regulation (EC) No. 1223/2009(Cosmetic Commission Regulation (EU) 2016/1198 of 22 July 2016 amending Annex V to Regulation (EC) No.; Regulation (EC) No. 1223/2009 of the European Parliament and of the Council of 30 November 2009 on cosmetic products). Indeed, methylisothiazolinone is now no longer permitted in leave-on products; it can, however, be used in rinse-off products, at a concentration of up to 0.01%. Allergens namely, alpha-isomethyl Ionone, Geraniol, Citronellol, Linalool, Hexyl Cinnamal, Piroctone olamine, Benzyl Salicylate, Limonene are allergens according to Annex III of EU Cosmetic Regulation 1223/2009(Cosmetic Commission Regulation (EU) 2016/1198 of 22 July 2016 amending Annex V to Regulation (EC) No.). The active ingredient, Piroctone olamine in SYN_01 that account for robust antifungal effects is a potential allergen as well (Schmidt-Rose et al. 2011a).

Potential future prospectives in shampoo formulation research may consider incorporating selective botanical bioactive compounds exhibiting microbiocidal or microbiostatic properties. These bioactive should target specific pathogens, such as Malassezia furfur, while preserving the natural scalp microbiome. Moreover, the formulations should prioritize scalp health with minimized to no usage of allergens, detergents or preservatives causing irritation or hypersensitivity and most importantly safe for the environment. Advancing this approach could develop effective and safer alternatives in dandruff treatment considering both therapeutic and ecological concerns. Future studies should also consider exploring mechanisms and long-term effects.

The release of synthetic shampoos containing fragrances, antibiotics, therapeutic drugs, allergens, preservatives and surfactants into aquatic environments is a significant threat(Liebig and Knacker 2007; Klaschka 2016; Couteau et al. 2019; Jyoti and Sinha 2023; Wirtu 2024). Few of them have even been detected in the natural water sources. In contrast, herbal shampoos frequently utilize natural, plant-derived ingredients that do not pose any health or environmental hazard. Nevertheless, manufacturers must ensure that natural shampoos do not contain chemicals that could be harmful to human health. Thus, a thorough assessment of the environmental impact of both synthetic and herbal shampoos is essential to ensure their responsible use and disposal.