Irritation by surfactants

Minimal irritation is another essential property for shampoos because the products can easily come into contact with sensitive parts of the body, including the eyes, during the hair washing process. Studies on skin irritation by surfactants show that irritation is usually not a problem with the long-chain alkyl sulfates [5-9], The presence of ethylene oxide groups reduces the irritation of these materials. 

Several toxicity, irritation, and sensitization phenomena will be summarized in this section with special reference to hair care products that contain surface active agents. Skin irritation by surfactants will be covered in some depth providing a few fundamental principles and useful relationships of skin irritation to surfactant molecular structure to provide guidance for formulating milder hair care products. A few important regulatory statutes will be summarized and referenced for further follow up as needed. 

The following five rules of thumb for skin irritation by surfactants are followed with only a few exceptions, and these can facilitate the development... 

Although we have not tested this effect for other types of surfactants, it is clear that molecular weight (size) does explain a large part of skin swelling. Because skin swelling correlates with skin irritation by surfactants, molecular weight must explain a large part of skin irritation. This is because... 

Vesicles are ideal systems for cosmetic apphcations. They offer a convenient method for solubilizing active substances in the hydrocarbon core of the bilayer. They will always form a lamellar liquid crystalline structure on the skin and, therefore, they do not disrupt the structure of the stratum corneum. No facUitated trans-dermal transport is possible, thus eliminating skin irritation (unless the surfactant molecules used for making the vesicles are themselves skin irritants). Indeed, phospholipid liposomes may be used as in vitro indicators for studying skin irritation by surfactants [14]. 

Many different protein denaturation tests have been developed to predict skin irritation by surfactants they vary both by the protein type and the way they assess protein denaturation. However, most of them provide a similar level of predictability as compared to the in vivo situation and the same type of limitations. Table 1 lists several of these tests and some of the most commonly used are briefly described below. 

Table 1 Protein Denaturation Tests to Predict Skin Irritation by Surfactants...

In addition to predicting skin irritation by surfactants, these in vitro tests have greatly increased the knowledge of the skin scientist concerning the mechanisms of irritation and on the cellular and molecular events occurring when surfactants contact the skin. The complexity of such events and the constant discovery of new molecules (cytokines) involved in skin irritation encourage development of in vitro models, and especially cell culture models, in order to better understand the role of these new molecules in less complicated systems than our whole body before confirming results in vivo. 

Other animal tests have been used to study skin irritation by surfactants or other chemicals and have been reviewed by Gabriel [50]. They are the mouse ear swelling test, the guinea pig immersion technique, the cumulative irritation test on rabbits, and the rabbit ear test. As their usage is continually declining, the reader is referred to Ref. 50 for further details. 

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

Muir, C.K. (1985). Opacity of bovine cornea in vitro induced by surfactants and industrial chemicals compared with ocular irritancy in vivo. Toxicol. Lett. 24 157-162. 

Furrer, P., et al. 2000. Application of in vivo confocal microscopy to the objective evaluation of ocular irritation induced by surfactants. Int J Pharm 207 89. 

The SC is subjected to various environmental chemical threats. Squamometry S was designed to test the effect of surfactants on the SC in vivo.6,7,14,64 Several studies have confirmed the reliability of such a method in predicting irritation by selected xenobiotics61,65-70 and protection afforded against them by diverse agents.62,71 As such, squamometry S appears to be a suitable method for evaluating... 

Molecular association between different surfactants makes the ingredients (system) milder to skin (e.g., adding cationic or amphoteric surfactants to anionic surfactants decreases the irritation by the anionic). 

To calculate relative irritation by products, simply take the sum of the irritation index of each surfactant multiplied by its concentration (weight concentration) in the product. Then multiply this sum by a normalization factor to place it on a scale between two known extremes in irritation for... 

P, G. M. Van Der Walk, J, P. Naier. E. Bleumink. Skin irritancy of surfactants as assessed by water vapour loss measuremems. J. Invest, Demaioi, 82 291-293. 1984... 

Toxicology Poison by intravenous route mildly toxic by ingestion severe eye irritant Uses Surfactant in cosmetics base, foaming agent, detergent for shampoos thickener Trade Name Synonyms Nikkol PMT [Nikko Chems. Co. Ltd... 

The observed synergism can be understood in the light of the work of Zeidler and Reese (62) who studied the swelling of the pig epidermis caused by surfactants when compared to the swelling effect of pure water. In contrast to anionic surfactants, betaines and amphoteric surfactants cause negative swelling of the skin relative to water. This may reduce penetration and irritation effects of the anionics. 

Observable toxic responses in the skin (irritation, allergic reaction) can be directly caused by the presence of surfactant molecules in the dermis, by inflammatory mediators (cytokines) liberated by keratinocytes, or by other substances penetrating the epidermis after the skin barrier function has been impaired by surfactants. The damage of hair fibers is closely related to the impairment of the cuticle layer, which can cause modifications in the mechanical and optical properties of the hair. Substantial differences exist between the mechanisms of skin damage and hair damage, but for the purposes of our discussion, only the common initial event of surfactant-keratin interaction will be considered. 

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