Effects of new cysteamine treatment on hair fibre properties and composition using thermal analysis and infrared-spectroscopy

Straight and smooth hair styles remain a key consumer trend across the world. Semi-permanent chemical straightening treatments can significantly reduce daily hair styling times and the need for straightening irons. A new chemical straightening system has been developed that uses cysteamine as the reducing agent in the treatment product, a low level of hydrogen peroxide in the neutralising conditioner to control malodours and heat treatment to set the style in place. The experiments reported here investigate the effects of the treatment on hair fibre properties and composition using MDSC (Modulated Differential Scanning Calorimetry) and FTIR (Fourier Transform Infrared) spectroscopy. The effects of the cysteamine treatment are compared with the effects of a standard thioglycolate-based straightening treatment (or ‘anti-perm’). They are also compared with the daily use of straightening irons. To investigate the effects of chemical treatments, virgin Caucasian hair was treated once and then washed every day for 74 days. Hair samples were taken at 2, 28, 56 and 74 days for analysis by MDSC in water, Attenuated Total Reflectance (ATR) and Transmission FTIR. To investigate the effects of straightening irons, hair samples were washed and straightened repeatedly using a standardised protocol. MDSC measurements showed that chemical and thermal straightening treatments all reduced the keratin denaturation enthalpy (ΔHD) irreversibly and to a similar extent over 28-40 days. However, after 74 days the effects of the thermal straightening were greater than the effects of both chemical treatments. Interestingly, the cysteamine treatment had a significantly greater effect on the denaturation temperature (TD) than the thioglycolate-based treatment. We speculate that this might be associated with greater plasticity of the matrix proteins, helping the straightening effects. FTIR measurements showed that the cysteamine treatment produced less cysteic acid in the outer cuticle layers than the thioglycolate-based treatment. These measurements confirm that all the straightening techniques tested here, chemical and thermal, have an effect on the structural integrity of the intermediate filaments in the cortex. However, they also show that the new cysteamine treatment (with lower levels of hydrogen peroxide in the neutralising conditioner) produces less oxidative damage in the cuticle than a standard perm treatment.