Brazilian keratin treatments do work to make curly hair straighter, more manageable, and shinier—but here's the catch: many salon products contain formaldehyde or formaldehyde-releasing compounds, despite being marketed as safe. The review found virtually no reported side effects, but that doesn't mean the formaldehyde exposure isn't a concern worth paying attention to.

This was a review article, meaning the authors gathered and analyzed existing research on Brazilian keratin treatments rather than conducting their own experiment.

Funding not disclosed in abstract