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:
Lipids in the hair can be damaged and stripped away;
Chemical changes to the structures within the hair shaft
These two changes will be discussed in further detail below.
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.
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.
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.
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.
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.
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.