Formaldehyde replacement with glyoxylic acid in semipermanent hair straightening: a new and multidisciplinary investigation C. Boga*, P. Taddei † , G. Micheletti*, F. Ascari*, B. Ballarin*, M. Morigi ‡ and S. Galli ‡ *Department of Industrial Chemistry “Toso Montanari”, Alma Mater Studiorum- University of Bologna, Viale del Risorgimento 4, 40136, Bologna, Italy, † Department of Biomedical and Neuromotor Sciences, Alma Mater Studiorum-University of Bologna, Via Belmeloro, 8/2, 40126, Bologna, Italy and ‡ Ilios srl, Via L. Basso 170, 47522, Cesena, Italy Received 11 April 2014, Accepted 08 June 2014 Keywords: chemical synthesis, glyoxylic acid, hair treatment, keratin, spectroscopy, straightening Synopsis OBJECTIVE: Formaldehyde is an effective and popular semiperma- nent hair straightener, but the severe consequences for human health due to its toxicity have prompted the search for safer alternatives. Different carbonyl compounds, including glyoxylic acid, have recently been proposed as promising candidates. Despite the interest in this topic, there is a lack of information about the interactions between hair keratin and straightener agents. This study addresses this issue to gain new insights useful in the devel- opment of new products for safe, semipermanent hair deformation. METHODS: The possible reactions occurring between carbonyl groups and nucleophilic sites on amino acid residues belonging to the keratin were investigated using as model compounds some aldehydes and amino acid derivatives. Raman and IR analyses on yak hair subjected to the straightening treatment with glyoxylic acid in different conditions were carried out. Scanning electron microscope (SEM) analyses were carried out on yak and curly human hair after each step of the straightening procedure. RESULTS: The reactions between aldehydes and N-a-acetyl-L- lysine revealed the importance of the carbonyl electrophilicity and temperature to form imines. Raman and IR analyses on yak hair subjected to the straightening treatment evidenced rearrangements in the secondary structure distribution, conformational changes to the disulphide bridges, a decrease of the serine residues and forma- tion of imines. It was also indicated that straightening produced major conformational rearrangements within the hair fibre rather than on the cuticle. CONCLUSION: This investigation revealed the role played by the electrophilicity of the carbonyl on the straightener agent and of the temperature, closely related to the dehydration process. Raman and IR studies indicated the involvement of imine bonds and the occur- rence of a sequence of conformational modifications during the straightening procedure. SEM analyses showed the effectiveness of the treatment at the cuticular level. R esum e OBJECTIF: Le formald ehyde est un agent d efrisant semi-permanent pour cheveux efficace et populaire, d efriser mais les graves con- s equences de son utilisation sur la sant e de l’homme dues  a sa toxi- cit e ont stimul e la recherche pour de plus s^ ures alternatives. Diff erent compos es carbonyl es, y compris l’acide glyoxylique, ont  et e r ecemment propos e comme candidats prometteurs. Malgr e l’int er^ et pour ce sujet, il y a un manque d’information sur les inter- actions entre la k eratine des cheveux et les agents defrisant. Cette  etude aborde cette question dans le but d’acqu erir de nouvelles connaissances utiles  a l’ elaboration de produits plus s^ urs qui seront utilis ees pour obtenir la d eformation semi-permanente des cheveux. M  ETHODES: Les possible r eactions entre les groupes carbonyles et les sites nucl eophiles des r esidus d’acides amin es appartenant  a la k eratine ont  et e  etudi ees en utilisant pour mod eles des ald ehydes et des d eriv es d’acides amin es. Des analyses Raman et IR sur des poils de yack soumis au traitement de d efrisage avec l’acide glyoxylique dans diff erentes conditions ont  et e r ealis ees. Des analyses par microscope  electronique  a balayage (SEM) ont  et e effectu ees sur des poils de yak et des cheveux boucl  es humains apr es chaque  etape de la proc edure de d efrisage. R  ESULTATS: Les r eactions entre des ald ehydes et des N-a-ac etyl- lysine ont r ev el e l’importance de l’ electrophilicit e du carbonyl et de la temp erature pour former des imines. Les analyses Raman et IR sur les poils de yak soumis  a un traitement de d efrisage ont mis en evidence des r earrangements dans la distribution de la structure secondaire, des changements conformationnels de ponts disulfures, une diminution des r esidus de serine et la formation d’imines. Il a  egalement  et e indiqu e que le d efrisage produit des r earrangements conformationnels majeurs au sein de la fibre capillaire plut^ ot que sur la cuticule. CONCLUSION: Cette  etude a r ev el e le r^ ole jou e par l’ electrophilic- it e du groupe carbonyle sur l’agent d efrisant et par la temp erature,  etroitement li e au processus de d eshydratation.  Etudes Raman et IR ont indiqu e l’implication des liaisons imines et la presence d’une s equence de les modifications conformationelles au cours de la proc edure de d efrisage. Les analyses SEM ont montr e l’efficacit e du traitement au niveau de la cuticule. Introduction Since the first decade of the last century, the permanent deformation of human hair has been achieved with the use of chemical agents. In fact, due to the elastic properties of hair [1], when both waving and straightening are obtained by thermal treatment, only a tempo- rary deformation that lasts only until the next wash is obtained [2], Correspondence: Carla Boga, Department of Industrial Chemistry “Toso Montanari”, Alma Mater Studiorum- University of Bologna, Viale del Risorgimento 4, 40136 Bologna, Italy. Tel.: +39-51-209-3616; fax: +39-51-2093654; e-mail: carla.boga@unibo.it © 2014 Society of Cosmetic Scientists and the Soci et e Franc ßaise de Cosm etologie 1 International Journal of Cosmetic Science, 2014, 1–12 doi: 10.1111/ics.12148