Formaldehyde, a chemical found in many hair straightening products, poses "an unreasonable risk to human health," according to a new warning issued by U.S. health authorities. In a long-awaited review of the safety of this substance, which is used in many industries from textiles to construction, officials warned that formaldehyde, which "is nearly everywhere," increases the risk of cancer.

There have long been concerns about the presence of this substance in chemical hair straightening treatments. Under names like formaldehyde, formalin, or methylene glycol, these substances are used to relax hair curls by interacting with keratin, the protein that helps make up hair.

However, when the treatment is applied using heat - whether through blow-drying or straightening - formaldehyde gas is released into the air, which is a colorless gas. When inhaled, it can cause irritation to the eyes and respiratory system at best, and at worst, may increase the risk of head and neck cancer in the long term.

These risks are particularly heightened in poorly ventilated areas such as salons, bathrooms, or bedrooms, increasing the need for caution and awareness regarding the use of these products that contain formaldehyde.