Skin 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. 

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... 

Table 3 Correlation Between Collagen Swelling and Skin Irritation by Anionic Surfactants...

Emulsions of fatty- and petroleum-based substances, both oils and waxes, of the o/w type are made by using blends of sorbitan fatty esters and their poly(oxyethylene) derivatives. Mixtures of poly(oxyethylene(20)) sorbitan monostearate (Polysorbate 60) and sorbitan monostearate are typical examples of blends used for lotions and creams. Both sorbitan fatty acid esters and their poly(oxyethylene) derivatives are particularly advantageous in cosmetic uses because of their very low skin irritant properties. Sorbitan fatty ester emulsifiers for w/o emulsions of mineral oil are used in hair preparations of both the lotion and cream type. Poly(oxyethylene(20)) sorbitan monolaurate is useflil in shampoo formulations (see Hairpreparations). Poly(oxyethylene) sorbitan surfactants are also used for solubilization of essential oils in the preparation of colognes and after-shave lotions. 

In a broad evaluation also the sulfosuccinate disodium laureth sulfosuccinate (DLSS) was a part of a variety of surfactants tested for their dermatological mildness, and some different test methods were applied [16]. Products were compared applying in vitro methods (Zein test, hemolysis) and in vivo methods (Duhring-Chamber test, skin mildness by intracutaneous test on mice and topical application on hairless mice, mucous membrane irritation according to the Draize procedure on rabbit eyes). In the Duhring-Chamber test the DLSS elicited no reactions in the animal tests it ranged in the least irritant third of the 15 products tested. 

The skin condition reflects the skin irritation elicited by a surfactant when applied. Skin surface appraisal is hence a means for assessing product mildness. 

As the central function of a shampoo is to cleanse the hair, the primary ingredient of a shampoo is a detergent (also known as a surfactant). Many shampoos, particularly those targeted for babies and children, claim to cause no eye irritation or sting. A no-tears formulation achieves this claim by carefully adjusting the nature of the surfactants. In particular, the identity and concentration of surfactants with an ionic or charged portion are controlled to minimize both eye and skin irritation. 

Sulfosuccinate Half Esters. To meet the demand for surfactants having low toxicity, especially low skin irritation, Nippon Shokubai commercialized a series of sulfosuccinate half esters of SAE, SOFTANOL-MES series, by it s own technology(32, 33, 34). 

SAFETY PROFILE Moderately toxic by ingestion and intravenous routes. Experimental reproductive effects. Human mutation data reported. An eye and human skin irritant. Many glycol ethers cause dangerous human reproductive effects. When heated to decomposition it emits toxic fumes of NO. A surfactant. See also GLYCOL ETHERS. 

CAS 119823-35-7. TM for a surfactant. Hazard Moderately toxic by ingestion and skin contact. A severe skin irritant. 

The skin irritancy of anionics can be diminished by the addition of positively charged materials such as protein hydrolysates (Taves, 1986) or long-chain amine oxides that interact with the anionic and decrease its tendency to adsorb onto the skin, or by polymers that interact with them (Chapter 5, Section 1B5) to reduce the CMC and, consequently, the concentration of monomeric anionic surfactant (Goddard, 1994), since it is the latter that produces the skin irritation. 

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