Effects for Hair?
While it is well-established that antioxidants are highly efficacious both when taken internally and applied to the skin via cosmetic preparations, it is natural to speculate whether or not they have equal value when applied topically to the hair, which is not a living cellular structure. Fortunately, the evidence indicates that there is plenty of benefit to be derived from the inclusion of antioxidants as components in formulations for rinse-off products, leave-in conditioners, and styling agents.
Vitamins and vitamin precursors such as Vitamin E, Vitamin C, and beta carotene have been found to have protective effects against environmental free radical assaults on hair. In a manner similar to sunscreens, these materials form a sort of interactive molecular shield against the elements, at least temporarily. By preventing the destruction of melanin and synthetic dye molecules in residence in the cortex of the hair strand, free radical scavengers can be quite useful in improving color retention and maintaining the health and integrity of hair. Experiments have also generated data that demonstrates the efficacy of topically applied antioxidants in mitigation of damage from both coloring and heat processes.
Oil soluble vitamins such as α-tocopherols and beta-carotene and vitamin A and lipophilic plant extracts are the more common antioxidants found in hair care preparations. The reason for this is that due to exposure to air many reactive oxygen species are generated in the aqueous phase in the bottle of product, where water soluble vitamins such as ascorbic acid (Vitamin C) would be present. The ascorbic acid is then rapidly depleted via oxidation reactions with the free radicals, and is thus comparatively short-lived in its availability to perform its preferred function on the hair.
One method chemists have used to circumvent this problem has been esterification of the ascorbic acid, which converts it to a lipophilic substance and increases its duration of efficacy. However, this additive is more expensive and diminishes its potential to scavenge radicals in the aqueous phase when hair is wet, which is when it is needed.
Furthermore, it is the assertion of research chemists at Mibelle Biochemistry in Switzerland that the inclusion of both water soluble and oil soluble antioxidants provides the best range of protection. For this reason they have been developing methods to include more stable water soluble antioxidants and blends (such as grape seed extracts + α-tocopherols) that provide highly effective protection of the cuticle and cortex, even in rinse-off products. Another research team has taken the approach of encapsulating ascorbic acid in micelles comprised of a nonionic surfactant (Polysorbate 80) and mixed tocopherols. This nanoemulsion is supplied as a gel-like aqueous solution that is easily mixed into a formula. The Vitamin C remains protected and active for a greater duration due to being in the interior of the micelle.
ConclusionOur hair is being constantly bombarded by reactive species of molecules that slowly tear apart the very complicated biopolymeric structure of each strand. Without adequate protection, especially for longer hair, the damage grows continually worse until it becomes very evident. Color fades quickly. The surface becomes rough and porous. Tangles, breakage, and frizz become the norm. Curly hair, which has a rougher surface than straight hair is even more susceptible to this type of degradation. Fortunately, it has been found that some botanical oils, vitamin E, vitamin C, and beta carotene do indeed provide some protection against these environmental sources of free radicals. They also provide emollient properties and other benefits to the hair, and thus seem to be good additions to products for curly hair. They are not substitutes for wearing a hat and treating your hair kindly though, so protect those tresses!
 F. Zülli, E. Belser, M. Neuenschwander & R. Muggli, Antioxidants from Grape Seeds Protect Hair Against Reactive Oxygen Species, Mibelle AG, Switzerland, http://www.mibellebiochemistry.com/publications/gsp-tantioxidants.php  Behnam, Dariush (Rossdorf, DE), Aqueous solution of ascorbic acid and method for producing same, United States Patent 6774247, 2004, AquaNova German Solubilisate Technology (AGT) GmbH (Darmstadt, DE) http://www.freepatentsonline.com/6774247.html