Formaldehyde is a chemical compound used as a precursor in various industrial processes and hair straightening products. It is classified as carcinogenic in humans. Considering the importance of the topic, this review aims to identify and characterize the health risks that formaldehyde chronic exposure involves and to describe the existing evidence of its main toxic effects as well as the risk factors during the application of this compound in the hair straightening process. For this purpose, a literature review was carried out by using the PubMed database, limiting it to studies conducted between 2010 and 2020. A total of 126 publications were found, for which a relevance analysis was performed, and those that studied the effects after chronic inhalation of formaldehyde in humans were selected. Finally, this search resulted in 75 publications. Among the harmful effects of formaldehyde a...