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Shampoo is one of the most widely used personal care products. To produce high-quality shampoo, using the right ingredients in the proper proportions is essential. Among all the ingredients in shampoo, surfactants are the core ingredients, as they contribute most to the fundamental function of shampoos, which is cleaning our hair and scalp.
Surfactants in shampoos help to clean our hair and scalp by acting as a foaming agent and cleansing agent. Surfactants can create a rich lather when the shampoo is applied for hair washing, and the lather helps distribute the shampoo evenly through the hair, ensuring that all parts of the scalp and hair are cleaned thoroughly. Surfactants act as a cleansing agent in the way of lowering the surface tension of water and their hydrophobic tails bind to the dirt and grease, while their hydrophilic heads interact with the water in the cleaning solution. This combination allows surfactants to emulsify and lift off dirt and grease particles from our hair and scalp, effectively cleaning it.
Surfactants can also contribute as a conditioning agent and a shampoo body texture enhancer.
However, so many surfactants are available on the market, and not all surfactants are created equal. Choosing the right one can make all the difference. This article will discuss how to choose the best surfactants for shampoo manufacturing.
Surfactants, short for “surface active agents,” are compounds that are used in a variety of applications to reduce the surface tension between two different substances. They have both hydrophilic (water-loving) and hydrophobic (water-fearing) properties, which allows them to interact with both water and oil-based compounds.
Surfactants can be found in many everyday products, such as detergents, shampoos, soaps, and cleaning agents. They are also widely used in the industries of food, pharmacies, plastics, paper, and textiles. Surfactants can be classified into four main categories: anionic, cationic, nonionic, and amphoteric.
Anionic surfactants are surfactants that have a negatively charged functional group, and they are the most common type of surfactant used in shampoo manufacturing. They are known for their strong cleaning ability and lathering properties. Examples of anionic surfactants used in shampoo include sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES). However, these surfactants can be harsh on the scalp and hair, leading to dryness and irritation. So in recent years, there is a trend of replacing SLS and SLES with more gentle anionic surfactants, such as amino acid surfactants, to achieve ‘sulfate-free’ shampoos.
Contrary to Anionic surfactants, Cationic surfactants are positively charged. They have good bactericidal and anti-static properties. So they are commonly used as a disinfectant and conditioning agent in a variety of home care and personal care products. Typical Cationic surfactants include Cetyltrimethylammonium chloride and Benzalkonium chlorid.
However, Cationic surfactants will interact with the Anionic surfactants and, in many cases combine to form an insoluble salt. So in shampoo formulations, where Anionic surfactants commonly exist, traditional Cationic surfactants can not be used. Cationic polymers are used in this case to offer conditioning properties and to formulate 2-in-1 shampoos.
Nonionic surfactants do not carry an electrical charge and they are generally less harsh than other types of surfactants. They are used in shampoo and other personal care formulations for their mildness and their outstanding ability to create a rich and creamy lather. Additonaly, Nonionic surfactants often have good thickening ability which can help to build a thick body texture for the shampoo. Examples of nonionic surfactants used in shampoo include cocamide DEA and Cocamide MEA.
However, there are some Nonionic surfactants that don’t have these favorable properties to use in shampoos. They are Alcohol ethoxylates(common examples are AEO-7 and AEO-9) and Alkylphenol ethoxylates(common examples are NP9 and NP10). They are harsh on the skin; they are defoaming; and they do not help to thicken a solution.
Amphoteric surfactants, also known as zwitterionic surfactants, have both positive and negative charges and can behave as either anionic or cationic, depending on the pH of the solution.
They are becoming more commonly used in shampoo formulations and other personal care products, due to their ability to decrease the irritancy of the formulation while increasing the active content level. Amphoteric surfactants also provide thickening and conditioning properties.
Examples of Amphoteric surfactants commonly used in shampoo include Cocamidopropyl Betaine, and Cocamidopropylamine Oxide.
When selecting surfactants for shampoo manufacturing, it is essential to consider several factors, including:
Surfactants are primarily responsible for cleansing the hair and scalp. Therefore, it is important to choose a surfactant that can effectively remove dirt and grease from our hair and scalp yet without leaving the hair feeling dry or stripped.
The foam produced by the surfactant helps distribute the shampoo through the hair and scalp evenly and holds dirt and oil in suspension for easy rinse offer with water. A rich foam also provides a pleasant user experience. Therefore, a surfactant that produces a rich and stable foam is desirable.
Some surfactants can potentially cause irritation to the skin, scalp, and eyes, so it’s crucial to choose a mild surfactant that is gentle and non-irritating. Sodium lauryl sulfate or SLS has excellent foaming and cleansing properties and was once a top choice as a shampoo surfactant. However, in recent years, it’s been increasingly criticized to be irritating, and its place has been taken by milder alternatives including Sodium laureth sulfate(SLES), Alpha Olefin Sulphonate, and Amino acid surfactants.
Thickness and viscosity determine the body texture of a shampoo, which is very crucial for the success of a shampoo product. A proper thick and viscous body is good for applying the shampoo to our hair and it also gives the consumer a good aesthetic appearance, which enhances his/her confidence in its hair-washing performance.
The choice of surfactants affects the thickness and viscosity of the shampoo. Thicker shampoos usually contain surfactants of higher molecular weight. Cetyl alcohol and Cetearyl alcohol are commonly added as thickeners. Some surfactants such as Cocamide DEA(CDEA), Cocamide MEA(CMEA), and Cocomidopropyl Betaine(CAPB) can also help to build viscosity through surfactant synergy effects.
Commonly, more than one surfactants are present in a shampoo formulation for surfactant synergy to achieve the best overall performance at a lower cost. It’s essential to ensure different surfactants are compatible with each other. As here above mentioned, Cationic surfactants are not compatible with Anionic surfactants.
See also:Surfactants must also be compatible with other ingredients in the shampoo formulation, such as thickeners, conditioners, and preservatives.
As surfactants usually take up the largest portion of a shampoo formula. The cost of the surfactant can largely impact the overall cost of the shampoo, so it’s important to choose a surfactant that provides good value for money.
Some surfactants can have negative environmental impacts, such as being toxic to aquatic life, being hard to degrade in nature, or using unsustainable sources. Therefore, it’s important to choose a surfactant that is environmentally friendly.
The use of certain surfactants may be restricted or prohibited by regulations, so it’s essential to choose a surfactant that is compliant with relevant regulations. A good place for checking the potential use restrictions of a surfactant(or any other ingredient) in personal care products is the Environmental Working Group(EWG).
Different surfactants may perform differently under various conditions, such as pH range, hard/soft water, or in different temperatures, so it’s important to consider the intended use and the specific properties of the surfactant for optimal performance.
Some of the most commonly used surfactants in shampoo manufacturing are:
It’s important to note that some of these surfactants may be harsher than others, and different individuals may have different sensitivities to them. Some people may prefer to use sulfate-free shampoos, which use gentler surfactants or none at all.
Choosing the right surfactants is essential for producing high-quality shampoo. Consider factors such as performance, mildness, cost, compatibility, hair type, formulation, environmental impact, and regulatory requirements when choosing surfactants for your shampoo. By carefully selecting the right surfactants, you can create a shampoo that effectively cleanses and nourishes the hair while being gentle on the scalp and the environment.
There are numerous articles describing the results of the assessment of toxic effects of surfactants using biotesting methods [ 10 13 ]. Micro- and macroalgae, seed plants, invertebrates, fish and bacteria are frequently used as test objects in toxicity bioassays [ 6 14 ]. Summarizing the published data, the following conclusion could be made: the luminous bacteriaandhave the greatest sensitivity and rapid response time to the toxic effects of surfactants in wastewater among other bioassays [ 8 15 ]. This result raises the question as to how surfactants affect the molecular level of luminous bacteria, resulting in their great sensitivity to these substances. To answer this question, investigating the sensitivity of enzymes from the luminous bacteria is a desired acceptable option. Here, a bacterial coupled-enzyme system, which involves two enzymes, namely, NAD(P)H:FMN-oxidoreductase and luciferase (Red + Luc), is usually used as a convenient and rapid tool to estimate toxicity in environmental monitoring [ 16 ]. The principle of bioluminescent enzymatic bioassays is to identify toxic properties of chemicals and mixtures based on their influence on the parameters of bioluminescent coupled-enzymatic reactions [ 17 ]. The bioluminescent coupled-enzyme system was previously shown to have sensitivity and specificity to substances, such as heavy metals, pharmaceuticals, quinones, etc. [ 16 20 ]. Moreover, the Red + Luc enzyme system was employed for the environmental bioassay of soil systems [ 21 26 ].
Surfactants have a widespread occurrence, not only as household detergents, but also in their application in industry and medicine. Previously, amphiphilic surfactants have been shown to have a positive impact on the adsorption of pollutants from soil and water samples [ 1 ]. Amphiphilic surfactants can also be used in drug production [ 2 ]. On the other hand, surfactants are predominant water pollutants due to urban and municipal wastewater discharges [ 3 ]. There is no doubt that the presence of surfactants in the natural environment might lead to toxicity effects of the surfactants on the cellular or molecular level of the organization of living things. For instance, surfactants are carcinogenic agents, and they show high chronic and sublethal toxicity effects on aquatic organisms, usually at concentrations from 0.4 to 40 mg/L [ 4 ]. However, when ciliateswere used as test organisms, they showed a 50% lethal dose (LD) for surfactants at concentrations from 0.09 mg/L [ 5 ]. Furthermore, the toxicity features of surfactants depend on their hydrocarbon chain length and degree of linearity [ 6 ]. Basically, the chemical structure of surfactants correlates with their toxicity level [ 7 ]. For example, anionic surfactants are more toxic than non-ionic surface-active agents [ 8 ]. However, antagonistic interaction was shown under the joint action of different surfactants [ 9 ].
The effect of commercial surfactants (CTAB, Tween 80, SLS) on the bioluminescent bacteriawas determined ( Figure 2 ). The results demonstrate that the marine luminous bacteria did not show any valuable sensitivity to the presence of the CTAB and Tween 80 samples. The luminescence intensity of the bacteria did not change in the presence of the surfactants. On the other hand, the presence of the SLS samples affected the luminescence intensity of the bacterium strain. The higher the concentration of SLS added, the lower the intensity of luminous bacterium luminescence measured because among the three different types of surfactants investigated, the bioluminescent bacteriawas found to be the most sensitive to the effect of the SLS samples. Additionally, it should be noted that the concentrations equal to or above the CCM surfactant concentrations did not lead to a crucial reduction in the luminescence intensity of the bacteria. As for the coupled bioluminescent enzyme system, the median effective concentration value (EC) for SLS was calculated ( Table 1 ).
The effect of commercial surfactants of different types (Tween 80, CTAB, SLS) on the coupled-enzyme system Red + Luc was determined ( Figure 1 ). CTAB, at concentrations from 10M to its critical concentration of micelle formation (CCM), did not produce any impact on the activity of the Red + Luc enzyme system. In the same manner as CTAB, Tween 80 concentrations, which were lower than the Tween 80 CCM concentration, did not influence the activity of the coupled-enzyme system ( Figure 1 b). An opposite result was obtained for the SLS inhibitory effect on the Red + Luc enzyme system. The SLS samples decreased the activity of the coupled-enzyme system Red + Luc more effectively than the other surfactant samples. The concentration of SLS equal to 10M led to an approximately 55% lowering of the Red + Luc enzymatic activity. Additionally, the SLS concentration above and below its CCM showed almost the total inhibition of the Red + Luc enzyme system activity.
In the present paper, three types of surfactants (anionic, non-ionic and cationic) were studied. As a result, the surfactants were found to inhibit the activities of the Red + Luc enzyme system more than the light intensities of the luminous bacteria. The low activity of the cellular and enzyme-based assays in the presence of the surfactants at concentrations above CCM is attributed to the aggregation of the surfactant molecules into micelles [ 27 28 ]. This surfactant aggregation could cause oxygen diffusion limitation, which has negative effects on the process of the bioluminescence reaction for both the Red + Luc enzyme system and the luminous bacteria [ 16 29 ]. In this case, we mainly focused our attention on the speculation of the impact of the surfactants on the activities of the enzymatic assay system at concentrations that are lower than CCM. Firstly, these concentrations are more relevant and could help to understand how the chemical structure of the surfactant correlates with its toxicity effects. Secondly, surfactants at the CCM concentration and higher form a heterogeneous medium which is difficult to dissolve in water [ 27 ]. The formation of this medium results in the viscosity values of the reaction mixture in the presence of the surfactants, which could negatively affect the Red + Luc enzymatic activity. It was previously shown that the viscosity values of the reaction mixture above 3 cP negatively affected the activity of the Red + Luc enzyme system [ 30 ].
50 of the coupled-enzyme system for the surfactant was calculated to be 10−5 M and EC50 of the marine bacteria for SLS was equal to 10−2 M. Additionally, the ecological relevance for environmental toxicology implies an SLS concentrations from 0.5 to 4 mg/L because these concentrations are found in natural waters [P. phosphoreum
and the Red + Luc enzyme system might be a result that confirms the fact that the application of Tween 80 in bioremediation approaches [Comparing the sensitivity of two assay systems of one organism showed that both assay systems have a sensitivity to the anionic surfactant, presented by SLS. ICof the coupled-enzyme system for the surfactant was calculated to be 10M and ECof the marine bacteria for SLS was equal to 10M. Additionally, the ecological relevance for environmental toxicology implies an SLS concentrations from 0.5 to 4 mg/L because these concentrations are found in natural waters [ 31 ]. The data obtained in this study showed that SLS at these concentrations, from 0.5 to 4 mg/L, inhibited the activity of the Red + Luc enzyme system from 80% to 42%, which could be classified as a toxic effect. However, there were no significant effects when the luminous bacteria were exposed to this chemical ( Figure 2 c). It seems that the obtained toxicity of SLS at the above-mentioned concentrations is still a matter of debate. On the one hand, such toxicity will not be observed under natural conditions, which is due to the fact that enzymes are not exposed to the surfactants as they were in the experimental conditions of the present study. On the other hand, there is a need for additional investigations regarding the monitoring of the glowing activity of luminous bacteria under the exposure to long-term SLS concentrations, from 0.5 to 4 mg/L. Alternatively, cationic and non-ionic surfactants, CTAB and Tween 80, respectively, did not show any negative effects on the light intensity values of the marine luminous bacteria ( Figure 2 a,b) and the activity of the Red + Luc enzyme system ( Figure 1 a,b) at surfactant concentrations lower than CCM. Furthermore, a decrease in the concentrations of the surfactants to or below CMM in the coupled-enzyme system is probably associated with micelle formation and a change in the viscosity values of the reaction mixture. In case of the luminous bacteria, the same lowering of the light intensity values at concentrations of CTAB above CCM is connected with the surfactant antibacterial properties at concentrations above CCM [ 27 ]. Additionally, the absence of toxicity effects of Tween 80 on the luminous bacteriumand the Red + Luc enzyme system might be a result that confirms the fact that the application of Tween 80 in bioremediation approaches [ 32 ] is environmentally friendly.
P. phosphoreum
is not always a test system with a higher sensitivity to the surfactants. For instance, the guppy fishPoecilia reticulata
has a greater sensitivity to SLS. Such a sensitivity is likely to be connected with the ability of anionic SLS to create a film on the water surface, limiting oxygen supply into the water system and altering its dissolution [Moreover, the sensitivity of the applied assay systems was compared with other aquatic species exposed to these surfactants. The results are presented in Table 2 . The data presented in Table 2 show thatis not always a test system with a higher sensitivity to the surfactants. For instance, the guppy fishhas a greater sensitivity to SLS. Such a sensitivity is likely to be connected with the ability of anionic SLS to create a film on the water surface, limiting oxygen supply into the water system and altering its dissolution [ 33 ]. In addition, the luminescent bacteria involved in this study had sensitivity to SLS, which agrees with previously published results [ 34 ]. At the same time, it seems that there is a lack of data regarding the investigations of the Tween 80 toxicity. As was mentioned earlier, Tween 80 is used in surfactant-enhanced technology for the remediation of soils contaminated with hydrophobic organic compounds [ 35 36 ]. Therefore, it is quite difficult to find results regarding chronic and sublethal direct-toxicity effects of Tween 80 on any organisms. In this case, the results obtained in this paper regarding the toxicity effects of Tween 80 on the bioluminescent bacteria and the Red + Luc enzyme system might be used as an additional supporting point for approving the perspective soil remediation by the technology involving Tween 80.
−10 and 1 × 10−11 mol/L had a stimulating effect on the activity of Gram-positive bacteriumBacillus subtilis 6633
[As one can see, Table 2 presents only the cellular assay system for the assessment of the toxicity effects of the surfactants, rather than the enzymatic ones. Though, as shown in this study, the Red + Luc enzyme system has a greater sensitivity to SLS than the cellular one. The high sensitivity of the enzymatic assay systems is connected with the fact that enzymatic systems do not have the protection mechanisms that cellular systems have, such as a cellular membrane. Thus, the toxicity assessment of chemicals based on enzymatic assay systems could provide knowledge regarding the direct impact of chemicals on the most important metabolic pathways in an organism. Additionally, the enzymatic assay systems are free from the conditions when the toxicant has a positive effect on the informative parameters of the cellular assay system. For instance, it was reported that CTAB at concentrations of 1 × 10and 1 × 10mol/L had a stimulating effect on the activity of Gram-positive bacterium 38 ].
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