A cosmetic senna, Cassia obovata: 'neutral henna'.

Summary The powder made with leaflets of a senna, Cassia obovata Coll., is a cosmetic mis-called 'neutral henna' The traditional use of C. obovata is as a laxative. The principal active components of this laxative drug are sennosides A and B. In the Middle Ages the blend of henna (Lawsonia inermis) and senna was called 'the two hennas'. The traditional dermatological uses of C. obovata concern the henna component. The antibacterial activity of C. obovata (Table III) may explain these uses. Thin layer chromatographs showed that several C. obovata components are fixed to keratin (Table IV). The fixation hypothesis is given in Fig. 8. Bleached hair and, to a lesser extent, light (and white) hairs, turned golden light-brown or brown differing with the time of treatment. The hair absorbs the C. obovata components. In the initial stages uptake was linear with the square root of time, indicative of a diffusion process. In bleached hair diffusion is fast (7.5% uptake in 9 h), but there was no diffusion in dark hair. The sorption by hair pre-treated by hydrogen peroxide was greater than virgin hair, suggesting that the C. obovata components were chemically bound to the cysteic function of keratin. The initial 'uptake jump' suggests that the diffusion process was biphasic and/or several components diffused. The henna (Lawsonia inermis) seemed to enhance the penetration of C. obovata components. The hair treated by C. obovara became less hydrophilic: the water sorption of bleached hair decreased by 25%. The stress-strain curves and torsion-breaking of individual hairs, after drastic C. obovata treatment, showcd the mechanical properties of the treated hair were not very changed, but the hair was more heterogeneous. Microphotography showed that, after the drastic treatment, the hair seemed unaltered, but the cuticle scales were little opened. The C. obovata treatment crimps the hair. As a sunscreen, which is bound to keratin, C. obovata components provide ultraviolet protection.