Classification of High Curl Pattern Hair: A Systematic Review and Clinical Perspective

BACKGROUND: Hair type classification is crucial for developing personalized hair care, maximizing hair health, and selecting appropriate treatment for scalp disorders, yet it remains underutilized in clinical practice. AIMS: This review aimed to address three main questions: (1) How can hair types be defined according to specific shape criteria, without referring to race/ethnicity? (2) Why does certain hair exhibit a curly pattern, and how does curly hair behave uniquely? (3) How is the classification of curly hair clinically relevant to the development of seborrheic dermatitis? METHODS: PubMed and Google Scholar were the primary and secondary platforms used for the literature search, respectively. The scope of the search included English-language human studies published between 2000 and 2025 that investigated classification systems defining hair types based on specific shape criteria. RESULTS: The literature review revealed four mainstream hair classification systems: the André Walker Hair Typing System, the LOIS Hair Typing System, the FIA Hair Typing System, and the L'Oréal Curl Classification System. There are shared characteristics across the systems, as each was built on previous ones to incorporate nuances of different hair types and curl patterns. The L'Oréal Curl Classification System acknowledges the broader continuum of hair types by categorizing straight, wavy, curly, and coiled hair using four morphological parameters. CONCLUSIONS: There are several existing hair classification systems that dermatologists and other health care professionals can use to optimize communication with patients. Dermatologists' use of these classification systems and increased awareness of practices for high-curl-pattern hair could ultimately improve treatment outcomes. Curl pattern classification may also have predictive value in the treatment of scalp diseases (e.g., seborrheic dermatitis), but further validation is required.