Galliano et al.,2828 Galliano A, Saint Olive Baque C, Marty G, Nedelec B, Gauchet L, Littaye P, et al. Resistance of human hair cuticle after a shaking process in wet conditions: Comparison between Chinese and Caucasian hair. Int J Cosmet Sci. 2010;32:356-68. 2010. |
Clinical trial |
n = 12 (6 Chinese hair samples and 6 Caucasian hair samples) |
Thiol straightener |
Increased inter-scale distance, scale inclination and edge irregularity. |
Average size of particles extracted from hair after stirring in water for 30 minutes: different between ethnicities and proportionally greater increase in Chinese hair. |
Kaliyadan et al.,2929 Kaliyadan F, Gosai BB, Al Melhim WN, Feroze K, Qureshi HA, Ibrahim S, et al. Scanning electron microscopy study of hair shaft damage secondary to cosmetic treatments of the hair. Int J Trichology. 2016;8:94-8. 2016. |
Cross-sectional |
n = 25 (F:25) (19 subjects and 6 controls) |
Chemical relaxers |
In straightening only (n = 2): curly hair had grade 2 damage (severe cuticle lift, fissures or gaps with exposed cortex) and wavy hair had grade 0 (intact cuticle). |
In straightening associated with hair dye (n = 7): damage degrees from 1 (irregular cuticle without fissures or gaps) to 2. |
In the association of straightening, discoloration and hair dye (n = 1): grade 3 damage (partially exposed cortex). |
In the control group (wavy or straight hair): damage degree from 0 to 1. |
Bloch et al.,3030 Bloch LD, Goshiyama AM, Dario MF, Escudeiro CC, Sarruf FD, Velasco MVR, et al. Chemical and physical treatments damage Caucasian and Afro-ethnic hair fibre: analytical and image assays. J Eur Acad Dermatology Venereol. 2019;33:2158-67. 2019. |
Clinical trial |
Samples of Caucasian hair (straight dark brown; straight blond; wavy dark brown; and curly dark brown) and Afro hair. |
Ammonia thioglycolate |
71% reduction in Work (in Joules) for the combing of Afro hair. |
Greater color variation in dark brown and Afro-ethnic hair. |
Decreased tensile strength in all hair types. |
No additional loss of protein or tryptophan (except in Afro hair). |
Afro, curly and wavy dark brown hair: discreet opening of the scales, fissures and breakage. |
Lee et al.,3131 Lee Y, Kim YD, Pi LQ, Lee SY, Hong H, Lee WS. Comparison of hair shaft damage after chemical treatment in Asian, White European, and African hair. Int J Dermatol. 2014;53:1103-10. 2014. |
Clinical trial |
Asian, Caucasian, European and African American hair samples. |
Ammonia thioglycolate |
In straightening: Asian hair cuticles were the most resistant. The damage to the cortex was similar in the three groups. |
In straightening combined with commercial dye: the African American cuticle and cortex were the most resistant. |
The three groups showed similar patterns of cell membrane damage after straightening or straightening combined with dye. |
França-Stefoni et al.,1111 França-Stefoni SA, Dario MF, Sá-Dias TC, Bedin V, de Almeida AJ, Baby AR, et al. Protein loss in human hair from combination straightening and coloring treatments. J Cosmet Dermatol. 2015;14:204-8. 2015. |
Clinical trial |
Dark brown curly Caucasian hair. |
Ammonia thioglycolate, guanidine hydroxide, sodium hydroxide |
Additional protein loss in washing: dye (48%), ammonia thioglycolate (159%); guanidine hydroxide (188%); sodium hydroxide (276%). |
When combined with dye, ammonia thioglycolate and guanidine hydroxide did not cause a significant additional increase in protein loss. Sodium hydroxide did. |
Dyer et al.,3333 Dyer JM, Bell F, Koehn H, Vernon JA, Cornellison CD, Clerens S, et al. Redox proteomic evaluation of bleaching and alkali damage in human hair. Int J Cosmet Sci. 2013;35:555-61. 2013. |
Clinical trial |
European straight hair samples |
Sodium hydroxide |
Increased oxidative alterations, alkali-associated damage, increased dehydroalanine formation and side chain dehydration, and cysteine damage. |
McMullen et al.,3434 McMullen RL, Chen S, Moore DJ. Spectrofluorescent characterization of changes in hair chemistry induced by environmental stresses. J Cosmet Sci. 2011;62:191-02. 2011. |
Clinical trial |
Samples of dark brown European hair and Piedmont hair |
Sodium hydroxide |
Degradation of tryptophan and its metabolites. |
Dos Santos et al.,3535 dos Santos JD, Edwards HGM, de Oliveira LFC. Raman spectroscopy and electronic microscopy structural studies of Caucasian and Afro human hair. Heliyon. 2019;5:e01582. 2019. |
Clinical trial |
Afro and Caucasian white hair samples |
Ammonia thioglycolate |
Fiber lesions, with irregularities and cuticle detachment, and small undulations along its extension. |
Association of straightening with discoloration and straightening iron: irregular-contour hairs, cuticle detachment and deformation, and possible cortical damage. |
Mamabolo et al.,3636 Mamabolo T, Agyei NM, Summers B. Cosmetic and amino acid analysis of the efects of lye and no-lye relaxer treatment on adult black female South African hair. J Cosmet Sci. 2013;64:287-96. 2013. |
Clinical trial |
N: 5 (F:5, M:0) |
Sodium hydroxide and guanidine hydroxide |
Guanidine hydroxide: greater softness, smooth appearance, shine, and less dry appearance. |
The two products were similar regarding damage. |
The no-lye straightener showed fewer split ends. |
Cystine content is reduced with lye straightener and more intensely with no-lye straightener. |
Lysine decreased in relation to virgin hair for the two straighteners; however, with no statistical difference between them. |
Khumalo et al.,3737 Khumalo NP, Stone J, Gumedze F, McGrath E, Ngwanya MR, de Berker D. “Relaxers” damage hair: Evidence from amino acid analysis. J Am Acad Dermatol. 2010;62:402-8. 2010. |
Historical cohort |
n = 30 |
Chemical relaxers |
Cystine, citrulline (not always with statistical significance) and arginine decreased and glutamine increased in straightened hair. Cystine levels were lower in treated hair than in virgin hair, with levels similar to those found in trichothiodystrophy. |
Beach et al.,3838 Beach RA, Wilkinson KA, Gumedze F, Khumalo NP. Baseline sebum IL-1α is higher than expected in afro-textured hair: A risk factor for hair loss?. J Cosmet Dermatol. 2012;11:9-16. 2012. |
Clinical trial |
n = 36 (F:30, M:0) |
Guanidine hydroxide, sodium hydroxide, ammonium thioglycolate |
IL-1α and IL-1ra were detected on the scalp. |
After the straightening, the levels of IL-1α and IL-1ra on the crown and vertex were lower, but with no difference compared to the group that did not straighten the hair. |
It was not possible to demonstrate changes in specific inflammatory cytokines after use of straighteners. |
Tackey et al.,3939 Tackey RN, Bryant H, Parks FM. Cytokine expression correlates with differential sensory perception between lye and no-lye relaxers. J Cosmet Sci. 2013;64:111-7. 2013. |
Clinical trial |
Three-dimensional epidermis model |
Sodium hydroxide, guanidine hydroxide |
IL-1α: at 4h of application there was no significant difference between the groups of straighteners, and at 24h and 48h the no-lye straightener reached higher levels. |
IL-1ra: always higher with no-lye. |
Both types had similar IL-1ra/IL-1α ratios in the early phases(suggestive of lack of relationship with immediate discomfort after application) and late phases; however the no-lye straightener had a higher ratio at 24h. |
PGE2 levels were higher than in controls at all phases. |