This study uses various microscopy techniques to monitor the effects and extent of damage caused by UV radiation on the microstructure and physical nature of hair fibers. Field emission scanning electron microscopy (FESEM) is used to monitor the effects of UV irradiation on the physical nature of hair fibers.
Long-term UV irradiation/humidification cycling caues thinning and fusion of the surface cuticle cells, as well as fusion of the cuticular sheath into a solid, rigid and brittle unit.
Scale thinning and fusion observed during irradiation/humidification cycling are greatly reduced with UV exposure at low humidities without humidification cycling. However, upon post-treatment with water, fibers irradiated at constant low RH (without humidification cycling) show scale thinning and fusion of the surface cuticle cell similar to that of fibers exposed to irradiation/humidification cycling.
This indicates that photodegradation occurs at low humidities as well.
While chemical oxidation results in partial dissolution (1 h H2O2) and then complete solubilization (4 h H2O2) of the melanin granules, photochemical oxidation does not appear to significantly alter the physical nature of the melanin granules, even after long-term UV irradiation/humidification (95% RH) cycling. However, the severity of photodegradation of the protein (cuticle and melanin granules) during UV irradiation/humidification cycling becomes apparent upon contact of these fibers with alkaline hydrogen peroxide.
Such contact results in instantaneous degradation of the already photochemically degraded components within the surface cuticle cells and highly accelerated solubilization of the melanin granules. Microfluorometry. Diffusion rates of fluorescent dyes can be used to characterize and quantify hair damage from different oxidative processes, such as chemical and photochemical oxidation. This method is well-suited to determine the diffusion coefficients as a function of radial distance from the center of a fiber cross-section and is useful in delineating the radial distribution of photo-oxidative damage.
Ultraviolet (UV) microspectrophotometry. This technique is used to monitor the formation of photodegradation products in unprotected hair fibers caused by UV radiation. The technique has been extended to study the effectiveness of UV stabilizers in protecting hair fibers against such photo-oxidative degradation of hair proteins. It has been shown by this method that restriction of a UV stabilizer to surface deposition or even peripheral penetration, does not appear to be successful in preventing photo-oxidative degradation. However, uniform distribution throughout the hair fiber during the humidification cycle and high uptake levels of the stabilizer appears to provide photo-stabilization. The success of a UV stabilizer in preventing photodegradation seems to be dependent on its ability to diffuse into the hair fiber as a result of its solubility and affinity towards the fiber.
Sunlight and Bleaching:
The physical chemistry of both chemical bleaching and sunlight effects on human hair are described. Recently we have become more aware of the critical involvement of free radical chemistry on both chemical and sunlight oxidative processes for human hair, therefore these effects are included. The beta layers of the cortical lipids with their high density of double bonds with allylic hydrogen atoms are very sensitive to free radical propagation reactions which can degrade the lipids themselves and also lead to protein degradation. Over the past decade, our understanding of the biosynthesis and the structures of the melanin pigments has improved greatly; the most current biosynthetic pathway has been added to this Chapter. Initial oxidation reactions remove 18-MEA (this is the protectant waterproofing the hair has) and free lipids from the surface and between cuticle cells.
When metals like iron or copper are present free radical chemistry is increased leading to degradation of lipids and enhanced protein degradation not only at disulfide bonds but even at peptide bonds.
Oxidative cleavage of disulfide bonds inside cuticle cells also occurs. Degradation of disulfide bonds inside cortical cells occurs next as well as degradation of hair pigments. Other amino acid functional groups are attacked and oxidatively degraded. The is why Olaplex #1 & #2 in the form of a Stand-Alone Treatment is important for people that don't color their hair. With Olaplex the damage can be repaired.
I recommend all clients use the Olaplex #7 Oil on their hair when going outside as it has UV protection!
Thank you,Mags Kavanaugh!
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