## 1 Introduction  
Hair has an important psychosocial role throughout life, by influencing individual self-perception and helping in the creation of bonds between individuals. Despite being a physical feature, we can easily change its length, color and shape with a plethora of different hair cosmetic products available on market [1, 2]. Structurally, hair has a mesh-like organization composed mainly by keratin, for which the \(\alpha\)-helices are coiled by ionic forces, hydrogen bonds, van der Waals forces and disulfide bonds [3]. The weaker bonds can be easily broken and reformed by simply styling wet hair; however, this new shape is only temporary [2]. To permanently change the hair shape such that it persists through several washes with shampoo, it is necessary to reconfigure the disulfide bonds via the reduction and reformation of new disulfide bonds using perming and relaxing solutions [3, 4]. The permanent waaving is generally a two-step process based on the action of reducing agents, thioglyculates or bisulfite, followed by an oxidative agent, normally hydrogen peroxide [1]. The first step consists in the application of an alkaline reductive solution on the hair to disrupt the disulfide bonds. This alkaline solution, with a pH of around 9, promotes lifting of the hair cuticles and penetration of the solution onto the hair cortex. The perming solution is then washed from the hair, and a neutralizing solution containing an oxidative agent is applied over the hair to promote the formation of new bonds according to the new desired hair shape [2, 5]. Despite being a common procedure in hair styling, hair becomes extremely damaged after repeated chemical perming. This process promotes the removal of the hydrophobic top-layer of the cuticle; the appearance of cracks; the lifting of hair cuticles; the appearance of split ends; and changes in hair texture, hydration and gloss [3]. Besides the negative impact on the quality of the hair fibers, many of the products used during perming contain toxic chemicals, with a negative impact on human life and environment [6; 7; 8; 9; 10]. These chemicals may include alkaline agents, thioglycolates, guanidine and even formaldehyde [3]. The increasing consciousness about health and the environment worldwide has promoted the development of green formulations to replace the toxicity of the current perming methods. The development of innovative green hair cosmetic products is foreseen as the best alternative to the products available on the market, which is commonly composed of chemicals. There are already some nontoxic formulations for hair priming that were developed to substitute the current perming formulations. The alternative proposed by [PERSON] et al., 2017, is based on the use of keratin decapeptide sequences derived from the human keratin genome. These peptides replace the harsh alkaline reductive solutions, minimizing or even avoiding the damage caused to the hair fibers by chemical products [3]. In the work of [PERSON] et al., 2016, the capacities of cysteine and polycarboxylic acids to substitute the thioglycolates and the hydrogen peroxide were demonstrated, respectively. Cysteine, an amino acid with a thiol group and a strong reducibility, reduces the disulfide bonds, while the polycarboxylic acids, known to have the ability to crosslink diverse protein materials, promotes the formation of new disulfide bonds [5]. In this study, we explored the potential of bovine serum albumin (BSA), silk fibroin (SF), keratin and two recombinant fusion proteins (KP-UM and KP-Cryst) to be used on the development of alternative eco-friendly formulations to curl straight, Asian hair. The selected proteins present different structures and properties (Table 1) that might influence the protein's ability to model the hair. Serum albumin is the most abundant protein in mammal plasma and has several important functions. Particularly, BSA is a multifunctional protein with a remarkable ligand binding capacity, with the capacity to transport a variety of metabolites [16; 17].