Protecting hair fibre and colour from solar radiation

Solar radiation by itself can trigger a series of undesirable results, such as loss of colour, both natural and artificial, and changes in the superficial layer of hair, which affect the appearance and manageability of hair. In fact, it is considered that ultraviolet radiation is one of the most damaging environmental factors. Solar exposure is the main area responsible for the degradation of amino acids in the hair cuticle. These amino acids play a key role in the stability of hair proteins. The aggression of this radiation causes reactions of photooxidation of disulfide bonds, which participate in maintaining the overall integrity of hair keratin. Ultraviolet radiation:

•  Degrades cysteine to cysteic acid by excision of the S-S and C-S bonds.1
•  Degrades the lipids present in the cuticle, particularly in the epicuticle, which play a key role in the properties of the hair surface.

Nogueira and Joekes (2004)2 evaluated the effects of ultraviolet radiation and visible light on different types of hair (brown, blonde, red). This study found that both UVB and UVA radiation are the main areas responsible for the loss of hair proteins and changes in coloration. A cosmetic active ingredient (Kerarice) has been specifically designed to protect hair fibres from the oxidative damage generated by sun radiation. It has been obtained from the grain of Oryza sativa L. and its chemical composition is characterised by the presence of biofunctional peptides and amino acids, polysaccharides and phytic acid. The amino acid composition of the peptides present in the active ingredient is characterised by a high concentration of glutamic acid (up to 17%) and important amounts of aspartic acid, arginine, leucine, phenylalanine, serine, valine and tyrosine (up to 10%). As seen in Figure 1, up to 80% of these peptides are in the range of molecular weights between 500 and 3000 Da. The molecular weight of peptides is directly related to its function at a hair level, either at the cuticle due to its restorative and/or conditioning effect or also due to its ability to penetrate and exert a beneficial effect at the cortex level, which would result in an improvement of mechanical properties. According to Stern and Johnsen (1977)3 and Teglia et al. (1993)4 peptides with a molecular weight that is: w Low (<1000): can penetrate and perform a repairing action of the hair fibres from the inside; in Kerarice, this fraction represents more than 45%. w Medium (1000-3000): form ionic bonds or hydrogen bonds with the hair and, therefore, they have a repairing role of the cuticle; in Kerarice, this fraction represents around 42%. The main polysaccharide present in the active ingredient is amylopectin (Fig. 2). This is a water-soluble branched polymer composed of glucose units connected linearly by bonds ?(1?4). Proposed structural models assume that amylopectin forms double helices arranged in parallel, forming bonds ?(1?6) at the branching points. This type of branching gives it a molecular form similar to a tree. Each molecule of amylopectin can contain between 100,000-200,000 glucose units, and each branch is formed by 20-30 glucose units in length. This type of three-dimensional structure prevents an excessive accumulation of the active ingredient and hair matting, compared with normally used linear polymers. Another key component of the active ingredient, phytic acid, (Fig. 3) acts as an antioxidant agent by inactivating free radicals generated by radiation. It is described that it is capable of chelating metals, especially divalent metals, and of inhibiting lipid peroxidation, generated or not by these metals.5,6