Hair waving or straightening

Ingredients with the function of curling or straightening hair change the shape of the hair by affecting its internal bonds, primarily the disulfide bonds of keratin. Thanks to this, straight hair can be made more wavy, and curly hair can be made smoother and smoother. Such substances work specifically with the hair shaft, and do not take care of the skin, so their main task is to persistently change the shape, facilitate styling and consolidate the desired result for a long time. The official materials of the FDA note that hair smoothing and straightening products are used to straighten hair or smooth curls, and the procedure itself often combines chemical composition and heating; however, such products require careful use, as they can irritate the skin, eyes and damage hair if used improperly. (fda.gov)

Reducing agents or strong alkaline agents are most often used in this role. A typical example is Thioglycolic Acid and its salts, which are used in permanent perm formulations and some straightening systems.: they help to temporarily "rebuild" the hair structure in order to then fix the new shape. Another common example is sodium—Sodium Hydroxide or related hydroxides in relaxers; such substances loosen and change the structure of strongly curly hair, making it straighter. The SCCS Scientific Committee separately considered thioglycolic acid and its salts as cosmetic ingredients and emphasized the importance of strict conditions of use and warnings on the packaging. (health.ec.europa.eu)

For the product formula itself, these components determine not so much the texture as the chemical activity of the composition: the strength of the effect, the holding time and the final effect depend on them. Since changing the shape of the hair is associated with aggressive interference in the protein structure, products in this category can increase the dryness, fragility and sensitivity of the scalp. The FDA also warns that some smoothing systems can release formaldehyde when heated, so the safety of the procedure depends not only on the composition, but also on strict compliance with the instructions and conditions of use. (fda.gov)