Hair UV Protection Claim Support 101
- TRI Princeton
- 5 minutes ago
- 8 min read
Dr Paul Cornwell, Director at TRI
Dr Philippa Cranwell, Technical Content Creator at TRI
When it comes to hair care products, customers are often looking for items that protect hair from damage. This short article will outline what UV light is, how it causes hair damage, technologies available for mitigating this damage, and the tests that TRI can offer for claims substantiation. This article is part of a series of bite-sized educational articles available in the TRI Academy, including a companion article on heat protection claims support.
Introduction
A recent survey of US-based customers by Procter and Gamble presented at the International Conference of Applied Hair Science in 2021 showed that, when it comes to customer-perceived causes of hair damage, hair coloring and the use of hot implements for styling were a large factor, but spending too much time in the sun was also noted as causing damage. This is reflected in the requests that TRI receives from clients, and while we’re often asked to assess the protection offered by various items during styling and coloring, we’re increasingly being asked about UV protection claims for cosmetic items designed to protect hair from the sun’s rays.
Useful historical reviews on the effects of UV light on hair include: Hoting 1997, Signori 2004, Giancola 2019, and Malinauskyte 2019.
What exactly is UV light?
The sun emits a broad spectrum of electromagnetic radiation, ranging from high energy (such as gamma rays) to low energy (radio waves). Of this emitted energy, only a small part is observable by the human eye: visible light. Visible light ranges in wavelength from 380 to 750 nanometers, with the shorter wavelength corresponding to the UV end of the spectrum, and the longer wavelength the infrared end if the spectrum.
When considering the light that can cause harm to either skin or hair, we’re talking about the high energy UV component, which is known to accelerate the signs of skin aging, cause chemical changes to cells and can lead to skin cancer. This high energy UV light can be sub-divided into three categories: UVA, UVB and UVC. UVC light is stopped by the ozone layer and poses no risk to human health, but both UVA and UVB light can cause changes to biological material with adverse outcomes, such as accelerated ageing, cancers from changes to DNA, and burning.
While hair is not susceptible to cancer, when it comes to hair health there are other aspects that can be affected by exposure to UV radiation.
Hair lipids can be oxidized, weakening adhesion between cuticle layers and the cortex.
Melanins, the color compounds within the hair fiber, can be bleached.
Proteins can be altered, which can lead to holes in cuticle layers, leading to cuticle lifting.
Reactive oxygen species (ROS) from lipid oxidation can affect the peptide backbone, causing cleavage of peptide chains.
We’ll consider the science behind each of these effects in further detail, look at mitigation of the impact of UV, and claims testing that can be used for UV-protection products.
Oxidation of hair lipids
Lipids, comprising of both saturated and unsaturated fatty acids, are an essential part of the hair structure, providing a protective coating against the environment and keeping hair healthy. Of the fatty acids present on the surface of the hair, between 30 and 40% contain 18-methyl-eicosanoic acid (18-MEA), which binds to thiol residues in the amino acid cysteine that are present on the outer layers of the cuticle , Figure 2a. When this fatty acid is bound to the protein, it provides a hydrophobic barrier, protecting the hair fiber from water ingress, as well as lubrication to reduce friction between hair fibers.
However, 18-MEA, as well as other fatty acids present, are vulnerable to chemical changes through hair treatments, such as coloring, bleaching and perms, as well as exposure to UVA and UVB radiation. These changes mean that the fatty acids are lost from the hair surface, which leads to hair become dry and brittle, as well as losing springiness and luster.
In order to probe the mechanism of lipid oxidation under UV, researchers at Tokyo University of Technology investigated how wet hair was affected by exposure to UV light. They propose that exposure to UV causes formation of hydroxy radicals from linoleic acid, Figure 2b and c, which is present between cuticle layers. The peroxidized lipid is then a source of hydroxyl radicals that attack other lipids present, forming holes in the cuticle of the hair and damaging the hair fibers. It is conceivable that a similar mechanism would be followed for dry hair, although damage would be less exaggerated due to lower water content.
Bleaching of melanins
Melanins are important pigments that give the hair its color but can also exhibit photoprotective properties, likely through scavenging of molecular oxygen as well as through formation of reactive oxygen species such as superoxide and hydrogen peroxide. There are five types of melanin: eumelanin, pheomelanin, neuromelanin, allomelanin and pyomelanin. Humans can have eumelanin (which is black) and pheomelanin (which is reddish-brown) present in hair fibers, although some people only have one or the other.
Melanins are usually present in the hair’s cortex where, if the cuticle is intact, UVB light cannot reach. However, if the cuticle is compromised, for example through formation of cuticle holes, there is a risk that UV radiation could reach the melanin molecules and lead to degradation effects. Interestingly, eumelanin alone degrades very little under UV and visible light radiation. However, a mixture of eumelanin and pheomelanin, the pigmentation in light brown hair, shows degradation by both UVA and visible light with destruction of the quinone system occurring, which is the structural feature vital for the photoprotective properties.
Alteration of proteins
The proteins present in the hair cuticle and cortex can be affected by UV light, although the degree to which they are impacted depends upon the presence or absence of UV-sensitive amino acids such as tryptophan and tyrosine, which are especially sensitive to UVB. While cysteine is not noted to have large UVB absorption capabilities, the quantity present in hair may mean that there is a cumulative effect, especially after long UV exposure.
Tests that can probe UV-mediated hair damage
At TRI Princeton there are several test methods that we can use to probe the effects of UV on hair, or the protective properties that a product can provide. Our solar simulator can be used to mimic subjecting hair to high levels of artificial sunlight to induce hair damage, with subsequent analytical techniques used to quantify any changes. Commonly used techniques for analysis of hair damage include tensile testing, differential scanning calorimetry (DSC), repeated grooming, and dry combing testing techniques, all of which interrogate the physical properties of a tress.
DSC is the most popular technique used for heat protection claims. This technique looks at the structural integrity of hair keratins. Higher keratin denaturation temperatures reflect higher levels of protein cross-linking (i.e. less damage). It only needs a small amount of hair for testing (<50 mg), is fast to perform and is very sensitive to changes in protein structure and cross-linking. However, a major drawback is that it can only tell whether there is a UV protection effect or not, and it can’t be used for supporting quantitative claims. Figure 3 shows the results from a typical UV protection study using DSC. The data show how UV exposure damages protein cross-linking and reduces the denaturation temperature of hair keratins. It also shows how the application of the leave-on UV protectant product reduced the damage inflicted.
There are a couple of important things to consider when performing UV protection studies. Firstly, the level of irradiance, and the exposure time. At TRI the Q-Sun Xenon Test Chamber is set to simulate peak mid-summer sunlight close to the equator (irradiance = 0.67 Wm2nm1). The exposure time is then set to simulate a certain number of days of sun exposure.
Validation studies performed at TRI show that 1 hour of exposure in our Q-Sun creates equivalent hair damage to 4.5 hours in the sun in Nevada. We therefore place hair in the Q-Sun for 2-hour cycles, to simulate 9-hour real-life exposure (a long summer’s day). Product is usually reapplied before each cycle, if a longitudinal experiment is required, to reflect the fact that product will be reapplied each day and to avoid the effects of product degradation under the UV light. DSC experiments are also affected by absorption of treatments into the hair and interactions of ingredients with hair proteins. Therefore, at TRI, hair is often dialyzed in demineralized water for 48 h so that these artifacts are removed and only the UV protection effects are recorded.
It’s also possible to see how color of hair may have changed, for example if looking at the impact of UV light upon hair dyes through color fade, imaging the cuticle to see if UV-induced cuticle degradation is an issue and analyzing lipids present on the hair surface.
Ingredients for UV protection
While in this article we have discussed the damage caused by UV to hair through lipid-based oxidation, bleaching of melanins and oxidation of proteins and amino acids, it should be noted that these reaction pathways are complex with several competing mechanisms at play. However, in most cases it’s the generation and reaction of reactive oxygen species (ROS) and the subsequent oxidation-based pathways that cause the damage. And, with multiple mechanisms for oxidation, there are multiple options for oxidation prevention.
UV sunscreens: In some cases, it’s possible to add a UV-absorbing ingredient to a product, akin to a sunscreen in a skincare product. While this is a viable approach, there can be challenges in formulation and application, for example ensuring that the active deposits on the hair effectively, does not cause negative customer experience in relation to feel and greasiness, and does not degrade too quickly.
Chelating agents: Within degradation pathways, metals, specifically copper and iron, are known to aid the formation of ROS and can have a big impact on the radical chemistry that degrades the hair. Adding chelating agents, for example histidine can be one way of addressing this.
Antioxidants: Inclusion of antioxidants such as vitamin E, argan oil or tea extracts can be seen by customers as addressing both the trend towards naturally derived ingredients, as well as being milder and more environmentally friendly than the alternatives.
Sacrificial shields: In a way, organic sunscreens are sacrificial shields, and are designed to breakdown, protecting the tissue underneath. However, it is also possible to use applied proteins and oils as sacrificial molecules in hair products. This is a relatively unexplored area and warrants further study.
For further information about claims substantiation in relation to UV protection, please contact us today.