It helped us to identify where a theory about the observed phenomenon would belong within the myriad of curvature aspects, and, from that point, enabled the development of new theoretical constructs to explain the observed phenomenon. The model offers researchers a tool to obtain an overview of the available relevant research focus areas it also assists with comparative studies on curly hair and highlights areas in which more research is required. This model is presented in the final part of this paper. The ‘what’ question requires an answer for both growing and keratinized portions.Īnswering these questions through the literature review has led to the development of a curvature fibre model that formalizes successive but distinctive tiers of elements in curly hair research.

Curly fibre behaviour (the ‘how’ question) pertains mostly to the keratinized portion. Since hair curliness is generated in the growing portion, the ‘why’ question of the literature review is addressed at the follicular level. The terms more commonly used for the keratinized part are ‘hair shaft’, ‘hair fibre’ or simply ‘fibre’. Below the scalp, the growing portion is generated in the follicle above the scalp, the keratinized portion exists as a dead biological structure. Each hair fibre comprises two distinct portions: namely, the growing and the keratinized portions. This review aims to address three main questions which have shaped the field: what does curly hair look like (structurally), why does some hair curl and how does curly hair behave? To answer any of these questions, it is necessary to distinguish between the different macroscopic parts of a fibre, irrespective of its shape. The main purpose of this paper is to present a literature review that explores the different aspects of curly human scalp hair. This is especially true for curly hair fibres, where phenotype is usually described in race-dependent hair subjective terms. This lack of interconnectedness is not unusual for an interdisciplinary field, but nonetheless produces inappropriate associations or combinations of non-parallel concepts. It also became evident that, in many of the reports, there was a gap in the comprehensive understanding of how certain aspects under investigation relate to one another or to other important aspects relating to the hair fibre. Exploring the observed phenomenon in light of available theories and experimental findings on curly hair, a literature review revealed a diversity of intentions and investigation perspectives when studying hair in general (all scalp hair forms). The work presented in this paper arose from an interesting phenomenon observed during tensile studies of hair fibres of different degrees of curliness, in which curly fibres lost a significant degree of curl during the preparation process. The phenotypical nature of the curly fibre is explored by some, but, compared with the bulk of the investigations, the curly fibre is mostly an addendum in the field of hair research. The purpose of this paper is twofold: namely to present (i) a literature review that explores the different aspects of curly human scalp hair and (ii) the curvature fibre model as a systemized approach to investigating curly hair.Ī quick review of current and most recurrent topics addressed in hair research includes hair growth, loss, corrective practices/surgery, mechanical, physical and chemical properties, follicle morphology and activities, genetic controls, forensic investigations and clinical pathology. These categories were subsequently formalized into a curvature fibre model that is composed of successive but distinctive tiers comprising the elements in curly hair research. During the literature investigation, we systematically categorized elements of curly hair research into three basic topics: essentially asking why fibres curl, what the curly fibre looks like and how the curly fibre behaves. From our review, it appeared that the complexity of hair biology, combined with the variety of research subtopics, often results in uncertainty when relating different aspects of investigation. Besides the large amount of information on the topic, there was also great variability in research focus. A brief literature search produced thousands of research items. The phenotypical nature of curly fibres is only accurately understood within the larger scope of hair fibres, which are highly complex biological structures.

An attempt to understand and explain a peculiarity that was observed for curly fibres during experimentation revealed disparate literature reporting on several key issues.

Curl patterns