Beschreibung:
<jats:title>Summary</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>Hair chemical treatments, such as dyeing and straightening products, are known to cause damage that can be assessed by protein loss.</jats:p></jats:sec><jats:sec><jats:title>Objectives</jats:title><jats:p>The aim of this study was to evaluate the hair protein loss caused by combined chemical treatments (dye and relaxer) using the validated bicinchoninic acid (<jats:styled-content style="fixed-case">BCA</jats:styled-content>) method. Three kinds of straighteners, based on ammonium thioglycolate, guanidine hydroxide and sodium hydroxide, were evaluated and the least harmful combination indicated.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>Caucasian virgin dark brown hair tresses were treated with developed natural brown color oxidative hair dyeing and/or straightening commercial products based on ammonium thioglycolate, sodium hydroxide, or guanidine hydroxide. Protein loss quantification was assessed by the validated <jats:styled-content style="fixed-case">BCA</jats:styled-content> method which has several advantages for quantifying protein loss in chemically treated hair.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>When both treatments (straightening and dyeing) were combined, a higher negative effect was observed, particularly for dyed hair treated with sodium hydroxide. In this case, a 356% increase in protein loss relative to virgin hair was observed and 208% in relation to only dyed hair. The combination of dying and relaxers based on ammonium thioglycolate or guanidine hydroxide caused a small increase in protein loss, suggesting that these straightening products could be the best alternatives for individuals wishing to combine both treatments.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>These results indicated that when application of both types of products is desired, ammonium thioglycolate or guanidine hydroxide should be chosen for the straightening process.</jats:p></jats:sec>