Aqua-Mane-ia: The Science and Art of Water on Your Hair

Part 4. The Impact of Copper

Philippa Cranwell

Technical Content Creator

Summer: the sun, the sea, the pool, the daquiris….and the green hair….an affliction that usually affects blondes and often occurs from swimming in a pool. The technical term for green hair is chlorotrichosis, and, contrary to urban legend, it is the interaction between hair and copper salts that cause the green color rather than between hair and chlorine. However, copper can do more than just turn hair green. This article will consider copper and its interaction with hair, why chlorotrichosis occurs, if damaged hair is more at risk from turning green, and if there is anything that can be done to avoid it or treat it. As with the other topics discussed in this mini-series, the condition of the hair when it is exposed to the copper is key. Damaged hair (e.g. through bleaching) can lead to an increase in the likelihood of metal coordination.

http://news.bbc.co.uk/cbbcnews/hi/newsid_6190000/newsid_6197800/6197865.stm

Where does the copper come from?

Worldwide, copper is present in hair at levels of between 10 and 200 μg/g with minimal visible impact upon the hair fibers. However, copper can play a role in hair damage, especially when hair is exposed to UV light. The reason that most people notice hair turning green after swimming in a pool is that copper sulfate (CuSO4) is sometimes added to the water as an algaecide, which leads to raised copper levels in the water that leads to increased copper coordination to hair fibers and therefore a color-change. However, it’s not only in the pool that there is a risk. Coordination of copper salts to hair can also occur if a house has freshly installed copper pipes because freshly installed pipes do not have a layer of limescale build-up on the surface, which has a protective effect and inhibits leaching of copper(II) ions. In addition, water with a low pH (i.e. is acidic) can facilitate leaching of copper into the water supply that can subsequently coordinate to hair fibers.

Copper accelerates UV damage

In 2014, workers at Procter and Gamble found that there was an increase in levels of a protein degradation biomarker upon exposure of hair to both copper and UV light rather than just UV light, then in 2015 they further elaborated on this work. They suggested that under UV light reactive oxygen species (ROS) are formed, which can both damage the protein framework leading to degradation and oxidize any lipids present. The presence of copper, a redox-active metal, further enhanced this effect by promoting formation of highly reactive hydroxyl radicals that also oxidized proteins or lipids in the hair, and then rapidly degraded these oxidized species by further radical pathways (these pathways were not fully elucidated).

They postulated that the copper entered the hair from tap water and then displaced calcium ions, becoming chemically bonded to residues in the hair. The levels of copper were highest in the endo-cuticle, where the levels of sulfur-containing residues were lowest. Removing the copper residues was possible with shampoo containing a chelating agent, either N,N’-ethylenediamine disuccinic acid (EDDS) or histidine, where histidine was most effective.

Copper and chlorotrichosis

Recent work at TRI Princeton has also investigated how metal salts can ingress into the hair cuticle. To gain baseline data, tresses were washed in a copper sulfate solution and colorimetry was used to quantify the color changes, Figure 1.

Figure 1: Virgin blonde hair before (L) and after (R) treatment with a 0.5 ppm copper sulfate solution for one hour. The color-change is clearly observed.

Three methods where then compared to see if the greening of hair from copper could be avoided (by coating hair with a protective layer of oil) or remedied (by either washing affected hair with regular shampoo and conditioner, or an acidified shampoo with pH 3.4). Quantification of color change using colorimetry relies on two axes: the a axis, which is the red-green color-scale, and the b axis, which is the yellow-blue color scale.

Hair that was neither pre-treated with a protective agent nor washed after exposure (the control sample) had the smallest a value (derived from the CIELAB color space), with the lower a value indicating a comparatively greener hue, Figure 2. When exposed hair was washed five times either with 15% SLES solution, shampoo with pH 3.4, or was pre-treated with oil and then washed five times with 15% SLES solution, the a value was increased compared with control sample, showing a reduction in the green-ness. However, between the three modes of treatment there were minimal differences. The largest a value was observed when, after exposure to copper sulfate solution, hair was washed using a drug-store shampoo (a value: –8.25).

Figure 2: Plot showing change in α value for the tresses under investigation. The a value runs along the red-green color-scale, with a lower a value showing a comparatively more green hue.

Other metal salts in hair

To definitively prove which metal salts are coordinating with hair, ToF-SIMS, a type of mass spectrometry, is required. ToF-SIMS is a powerful technique that can identify the precise metal ions present in the hair fiber and their location. For example, metal species such as iron (Fe), aluminum (Al), calcium (Ca), magnesium (Mg), copper (Cu), zinc (Zn) and arsenic (As) can all be identified, Figure 3. This is useful when looking for ingress of metal salts into the hair. In addition, removal of these metal salts using different techniques can also be monitored.

Figure 3: Data generated using ToF-SIMS, demonstrating the distribution of specific elements in a hair cross section, after soaking in water containing varying metal salts.

The science part

In water, copper sulfate ionizes into two distinct ions: copper, present as Cu(II), and sulfate, Figure 4.

Figure 4: Possible hydration shell of copper(II) and sulfate ions upon dissolution in water. The copper(II) salt will likely adopt a octahedral structure, with six water molecules coordinating through the lone pair of electrons on the oxygen atom. Hydration of the sulfate ion is less well-defined, although is likely to be through a δ positive hydrogen atom on the water molecule. This image is to illustrate the overall effect rather than provide a definitive structure.

The copper(II) ions can bind (chelate) with any lone pairs of electrons (e.g. on nitrogen or sulfur atoms) or negative charges on the hair surface, Figure 5a. Hair that has been chemically altered, for example by bleaching or perming, contains more negative charges on the surface due to chemical changes to the structure. This means that these hair fibers are more able to chelate with metal salts, leading to an increased instance of bonding to these metal ions, and explains why chemically damaged hair is more susceptible to chlorotrichosis.

As noted earlier, copper ions can be removed using a chelating agent. Over-the-counter chelating agents include N,N’-ethylenediamine disuccinic acid (EDDS), ethylenediaminetetraacetic acid (EDTA) and histidine, all of which can be incorporated into a shampoo formulation. Penicillamine is a medical treatment for chlorotrichosis that also works through chelation, and contains both a sulfur atom and a nitrogen atom. When penicillamine comes into contact with a copper(II) species, two sulfur atoms bind strongly to one copper(II) atom bringing the nitrogen atoms into close-proximity, therefore the nitrogen atom is also able to chelate by using the lone pair of electrons leading to a stable complex that can dissolve in water and be washed away, Figure 5b. The same principle applies to EDDA, EDTA and histidine, although the exact atoms binding in each will differ.

Figure 5: (a) Chemical interaction of common amino acid residues with copper(II) salts; (b) Chelation of copper by penicillamine.

That’s nice, but what do I need to do to keep my hair blonde when swimming in a pool?

As with all of the topics discussed in this mini-series, if hair is in good condition then it is less likely to be affected by environmental factors e.g. hard water, salt, or chlorine. Ensuring that hair is healthy and has minimal damage (e.g. through chemical straightening, perming or bleaching) goes a long way towards ensuring that hair does not go green in a swimming pool, as there are fewer carboxylate and sulfonate groups (present as cysteic acid) that are formed by oxidative cleavage of peptide bonds and disulfide bridges, respectively, during bleaching or straightening treatments. In addition, protecting hair from UV light will help mitigate damage from copper due to radical reaction pathways, therefore wearing a swimming hat will help. Washing hair with a chelating agent in the shampoo, e.g. penicillamine, will help prevent chlorotrichosis as a medical intervention, but TRI has also shown that a store-bought shampoo and conditioner also goes a long way towards restoring red-tones in hair and removing a greenish tinge.

How can TRI Princeton help me?

TRI Princeton provide a suite of analytical services that can measure the impact of water or metal ions upon the physical properties of the hair. For example, ToF-SIMS can be used to show distribution of metal ions within the surface of a hair fiber, colorimetry can show how red-green and blue-yellow hues change under different conditions, SEM can be used to visualize degradation of hair fibers upon exposure to pollutants, infra-red/Raman spectroscopy and mass spectrometry can interrogate structural changes to hair fibers, and Differential Scanning Calorimetry (DSC) can probe the hair protein structure.

Ernesta Malinauskyte

Director – Hair Research

Thank you to Ernesta, and the TRI Princeton hair research team, for providing supporting data.

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For further information in relation to how we can help, or to chat with one of our experts, please get in touch.

Aqua-Mane-ia: The Science and Art of Water on Your Hair

Part 3. The Impact of Chlorine & Sunshine

Daniel Craig swimming in a roof-top pool in Shanghai is an excellent advert for the advantages of swimming to keep in shape, but did he consider the impact that swimming in chlorinated water might have on his hair? Those of us who swim regularly may not have the physique of James Bond, but we have likely noticed that our hair feels dry or damaged afterwards; this is particularly pronounced when swimming in the sun. The culprit for this is chlorine, which is often added to the water for hygiene purposes. This short blog-post outlines exactly how chlorine in a pool damages hair, how additional exposure to UV light exacerbates its impact, and how to mitigate against any lasting damage.

How does chlorine affect hair?

When hair is exposed to chlorinated water, there are two things that are likely to occur:

1. Lipids in the hair can be damaged and stripped away;

2. Chemical changes to the structures within the hair shaft

These two changes will be discussed in further detail below.

1. Lipids in the hair being damaged and stripped away

Although lipids in the hair only contribute only 2–6% of the hair’s overall weight, they play a vital role in keeping hair healthy and influencing shine, as well as contributing to perceptions in relation to hair manageability and feel. Lipids are found in both the cuticle and cortical cell membrane complex. They can be characterized as either exogeneous (deriving from sebaceous glands) or endogenous (deriving from hair matrix cells) and comprise of fatty acids, triglycerides, squalene, ceramide and cholesterol, although the exact structures present depend upon whether the lipid is exogeneous or endogenous, Figure 1. Losing these lipids will likely cause the hair itself to feel dry or unhealthy due to the loss of the natural barrier that lubricates the hair shaft and prevents both penetration of foreign matter and loss of internal moisture.

Within their chemical structures these lipids contain numerous single and double bonds, which can be attacked chemically upon exposure to certain environmental conditions, for example chlorinated swimming pool water or UV light. Any chemical changes to the lipids will affect their behavior, for example by increasing their hydrophilicity so they become more soluble in water and wash out of the hair more easily.

Figure 1: Structure of some lipids present on the hair fibers. Note the lack of functionality (i.e. OH, NH, COOH etc) which means they have a high degree of lipophilicity (greasiness).

Changes to lipid content on the surface of the hair can be measured using FT-IR spectroscopy, which detects the presence of chemical structures, or more specifically certain chemical bonds, upon the surface of the hair fibers. Comparing lipid content before and after an external stimulus or treatment can give valuable insight into lipid behavior. Work completed at TRI has used FT-IR spectroscopy to monitor removal of lipids from hair fibers, which can also be used for claim substantiation, Figure 2.

Figure 2: FT-IR spectroscopy can be used to visualize lipids on the surface of the hair. (a) lipid content legend; (b) lipid content of virgin hair; (c) delipidated hair.

2. Chemical changes to the structures within the hair shaft

Chemical structures present within the hair shaft include melanin and keratin. Melanins are important for the hair’s color, and keratin for the structure and function. Let’s start by discussing melanins and how they are affected by chlorinated water.

Melanins – hair color:

The melanins are a group of compounds that create color in natural organisms. There are five types of melanin: eumelanin, pheomelanin, neuromelanin, allomelanin and pyomelanin. Eumelanin is the most common and is present in both skin and hair. A recent study investigated the impact of hypochlorous acid (HOCl) and sodium hypochlorite (NaOCl) on the color of hair, both chemicals likely to be present in a swimming pool. When hair was subjected to chlorinated water there was an impact upon hair color, even in the absence of UV light, and longer exposure of hair to chlorinated water led to a more substantial color-change. The greatest impact upon hair color was when hair was in chlorinated water and exposed to UV light, leading to significant color changes in both virgin brown and bleached hair.

The fact that changes occur in both the presence and absence of UV light suggests that there are two chemical reaction pathways that can be followed during hair-color degradation, and it is likely that the color-change is cause by chemical reactions with melanin(s): one pathway is likely dominated by a radical reaction pathway (in the presence of UV light; note that ionic reactions can still occur) and one is likely solely an ionic reaction pathway (in the absence of UV light). From the study it can also be concluded that when radicals are present more damage occurs, i.e. under UV light, evidenced by a more significant color-change.

In terms of the specific chemical changes occurring, it is likely that protonation, oxidation and/or chlorination will all feature, although whether oxidation and chlorination follow a radical or ionic pathway is unclear and would warrant further investigation; protonation is likely to be ionic. Nevertheless, all of these reaction pathways will change the chemical (and hence electronic) structure of the melanins, which will manifest as a visible change in hair color. In chemical terms, this is due to a decrease in electron delocalization along the aromatic back-bone of the melanin structure, which causes a shift in the wavelength of light absorbed by the melanin molecule, Figure 3.

Figure 3: Possible structure of eumelanin, a type of melanin.

Keratin – hair structure:

Keratin is the protein that plays a key role in the structure and function of the hair shaft. It comprises of many amino acids that are bonded together to form a protein. These amino acids contain ionic bonds, hydrogen bonds and disulfide bridges, all of which can undergo chemical reaction with chlorinated species in swimming pool water or under UV light. For example, the oxidation of sulfur in disulfide bridges generates sulfoxides or sulfonic acids, amino acid residues can be chlorinated, and aromatic rings can be hydroxylated, Figure 4. All of these chemical changes will affect proteins present in hair, leading to structural changes that can then lead to weakness or total destruction of the hair fiber.

Figure 4: Specific oxidation products with HOCl. (a) methionine and cysteine oxidation to a sulfoxide or cysteic acid, respectively; (b) oxidation of tryptophan; (c) oxidation of lysine or an α-amine; (d) oxidation/chlorination of tyrosine; (e) oxidation/chlorination of histidine. Villamena, F. (2017), Reactive Species Detection in Biology, From Fluorescence to Electron Paramagnetic Resonance Spectroscopy, Pages 13-64.

Chemical changes to keratin within the hair fiber, and therefore changes to the hair fiber’s strength, can be measured using Differential Scanning Calorimetry (DSC). DSC measures the temperature at which the hair proteins start to denature. A decrease in this temperature signifies that the proteins have been denatured, or chemically changed, during a treatment, therefore the hair fibers have been compromised.

TRI has undertaken work where denaturation of protein structure when exposed to UV light was quantified, Figure 5. These data show that longer exposure to UV light leads to more chemical changes of the hair proteins, shown by the decrease in temperature required for denaturation (ΔT). In addition it can be seen that chemically-damaged, bleached hair is significantly impacted by UV light, whereas unbleached and brown virgin hair are both affected by UV light, but to a lesser extent. These changes are likely due to formation of radical species due to exposure to the high-energy UV light, which then degrades the hair’s chemical structure.

Figure 5: DSC data showing changes in denaturation temperature for unpigmented virgin hair, medium brown virgin hair and bleached hair. Taken from Malinauskyte, E. (2019). Effects of Solar Radiation on Hair: Will Your Products Protect Against it? EURO COSMETICS, Vol. 27 (4) 22-25.

That’s nice, but what do I need to do to keep my hair healthy if I swim in a chlorinated pool outside?

The key things that can occur when swimming in chlorinated water are loss of lipids from the surface of the hair and chemical changes to the chemical structures within the hair, of which the changes to the melanins and therefore hair color are the most noticeable.

Loss of lipids can be remedied by using a shampoo that is gentle and replaces any lipids lost during general wear-and-tear, or by use of a leave-in hair treatment. Although UV light and chlorinated species present in a swimming pool both cause changes to hair color, the key to minimizing these changes is to avoid the combination of UV light with the chlorinated species. Avoiding the swimming pool entirely is one option, but simply shielding hair from UV light by wearing a swimming hat, or using a shampoo containing a UV filter, will protect hair to some extent.

Coming back to Daniel Craig, his hair would probably have been affected by the chlorinated water, but any major damage was likely avoided as he was swimming inside at night.

Our final blog article in this series will look at how copper can impact upon hair, leading to the dreaded green locks, stay tuned!

How can TRI Princeton help me?

TRI Princeton provide a suite of analytical services that can measure the physical changes of a particular set of conditions upon the physical properties of the hair. For example, SEM can be used to visualize degradation of hair fibers, infra-red/Raman spectroscopy and mass spectrometry can interrogate structural changes to hair fibers, and Differential Scanning Calorimetry (DSC) can probe the hair protein structure.

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For further information in relation to how we can help, or to chat with one of our experts, please get in touch

Beyond the Tube II: Exploration of Lip Hydration and the Impact of Lipsticks on Moisture Retention

Dr. Xuzi Kang, TRI Princeton

Postdoctoral Fellow

Last time, we talked about various testing methods for lipsticks, you can find them here. Now let’s talk about our lips!

Lips, those soft bits on our faces, do a lot more than help us chat or smile. They're different from the rest of our skin, which means they need a little extra love and care. If you're someone who loves lipstick, it's even more important to know more about the uniqueness of our lip skin.

The Distinctive Nature of Lip Skin

While we often consider our skin as a uniform organ, it varies significantly across different body parts. The skin on our lips, for instance, is incredibly distinctive:

• Thin but mighty: Unlike the rest of our body which has between 15 to 16 cell layers, the lip skin is wafer-thin, boasting only 3 to 5 layers [1]. This minimal layering makes lips susceptible to external factors and potential irritants.

• Missing moisture mechanisms: One reason your lips might feel dry more often is because they lack sebaceous and sweat glands. These glands are responsible for naturally moisturizing the skin. Plus, lips experience a heightened rate of water loss compared to other skin areas, making them prone to dryness.

Figure 1. Anatomy of lip skin [1].

Given these characteristics, it’s easy to see why lips demand special attention and regular hydration.

A Closer Look at Lip Hydration

At TRI Princeton, Dr. Xuzi Kang employed a corneometer to gain a deeper understanding of lip hydration. This device is both easy to use and non-invasive, making it optimal for accurately measuring the hydration levels in the superficial layers of the lip skin (the stratum corneum) [2]. This feasibility study engages 18 participants (9 male and 9 female) who are systematically chosen from a broad age range of 24 to 68 years old. Five testing points on the lips are chosen to test their upper and lower lip hydration. Participants are selected based on specific inclusion criteria which require them to be devoid of lip pathologies, skin lesions, or evident signs of lip dryness, thereby ensuring the integrity of the data pertaining to lip hydration. The objective was to determine differences in hydration levels between the upper and lower lips.

Figure 2. A: The 5 sampling locations on the lips; B: lower lip is 29% less hydrated than upper lip;

C: most panelists exhibit higher hydration in their upper lips (a), while only a few shows the opposite (b).

The Impact of Lipsticks on Hydration

Hydration is a significant concern for consumers, with some noting that while matte lipsticks do not transfer easily, they can be drying. To provide a deeper understanding of this phenomenon, the corneometer is used to evaluate lip hydration after a 2-hour application of the lipstick. Through a comparative feasibility study of the different types of lipsticks both on the arms and on the lips, distinct characteristics are identified and evaluated.

By analyzing the products' impacts both on the arm and lip skin, significant differences are found in hydration behavior based on the application site, a phenomenon illustrated in Figure 3. Interestingly, lip skin consistently shows a higher hydration level than arm skin, suggesting that lip skin is more susceptible to water evaporation, highlighting the fundamental differences between the two skin types in terms of composition and function.

It is found that all lipsticks tested, regardless of brand or type (including Vaseline - the positive control), enhance arm skin hydration to different extents, ranging from 16% to 67%; while lip skin. It is worth noting that the lip skin, which naturally holds more water, undergoes noticeable changes when in contact with different lipsticks (-13% to 57% hydration increase). This stresses the effect of lipstick formulations on hydration levels, and these data align with panelists' perceptions. Another interesting finding from this study is the hydration level in the upper lips compared to the lower ones, suggesting a possible difference in the anatomical and physiological attributes of the upper and lower lips. It’s worth noting that ATR-FTIR is available at TRI too to reliably measure hydration levels of our skin.

Figure 3. A: Arm and lip hydration levels are different;

B: arm and lip skin hydration change behaviors are different after 2h lipstick application.

Figure 4. There is a relatively strong correlation between hydration test results and panelists’ perception. Panelists rate their perception on a scale of 1 to 10, with 1 indicating very drying and 10 signifying highly moisturizing for the lips.

Wrapping It Up

In conclusion, the lip skin, inherently thinner and lacking sebaceous and sweat glands, is predisposed to quicker drying. Using a corneometer, this study offers a comprehensive examination of hydration levels on the lips and compares them to arm skin after lipstick application. Notably, because of their thin structure, lip skin has a higher hydration level than arm skin, and is more sensitive to different formulations of lipsticks. The application of various lipsticks showcases an impact on lip hydration levels, which correlates with the perceptions of panelists. Furthermore, the study shows a difference between the upper and lower lips in terms of hydration, shedding light on potential variations in their anatomical and physiological makeup. These insights not only deepen our understanding of lip skin hydration dynamics but also emphasize the influence of cosmetic formulations on the skin.

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For a deeper dive into this topic, Dr. Xuzi Kang will be presenting at the SCC annual meeting later this year. If you're keen to learn more, we highly recommend attending her session.

Reference

1. https://cocofloss.com/blogs/oral-health-guide/soften-your-lips

2. López Jornet, María Pía, Fabio Camacho Alonso, and Ana Belén Rodríguez Espin. "Study of lip hydration with application of photoprotective lipstick: influence of skin phototype, size of lips, age, sex and smoking habits." (2010).

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Looking to launch a new lipstick line or enhance your current line? For more information about lipstick testing methods, contact us.