Effects of chemical straighteners on the hair shaft and scalp()

BACKGROUND: The effects of chemical straighteners on the scalp and hair shaft are not fully known, although such substances are widely used. Hair straightening became popular in Brazil with the use of formaldehyde and its derivatives, despite the prohibition by the current legislation. OBJECTIVE: To identify changes in hair shaft and scalp caused by the use of chemical straighteners. METHODS: A search was performed using keywords in three databases from 03/16/2020 to 05/20/2020, with publications between the years 2000 to 2020. After applying the inclusion and exclusion criteria, 33 articles were selected for review. RESULTS: In some studies, hair relaxers were associated with eczema, desquamation, pain, burns, and inflammation in the scalp. Hair loss, damage to the shaft, alteration in the color of the hairs and in the composition of their amino acids were observed. Findings are variable across the studies. STUDY LIMITATIONS: The search was restricted to three databases, in two languages, different study designs were accepted. CONCLUSIONS: Straightening techniques can have side effects, including scalp inflammation, damage to the shaft, and hair loss. Its long-term effects remain unknown and further studies are necessary.