Rajendrani Mukhopadhyay/Washington DC, US

For the first time, researchers have used a quick, non-destructive microscopy technique to find out what happens to human hair when it's washed with shampoo products.

Eric Potma and colleagues at the University of California Irvine, US, collaborated with consumer goods giant Procter and Gamble (P&G) to analyse the mechanisms by which molecules in hair care products penetrate strands of hair, presenting their work at the recent American Chemical Society Fall meeting in Washington DC.

Autoradiography, scanning electron microscopy, and Fourier transform-based spectroscopic techniques are typically used to track the movement of molecules on hair fibres. But the methods are slow, explains Potma, and worse, they require that the hair be cut into small pieces. 'It is really not advantageous because you lose the nice structural component [of the strand],' he says. 

So for the first time, P&G and Potma's group are applying coherent anti-Stokes Raman scattering (CARS)  microscopy to chemically map hair. With CARS microscopy, there is hardly any sample preparation: 'You just take the entire hair strand, put it on a slide, and you're ready to image,' says Potma. 

The teams work with white hair because the melanin in dark hair disrupts the analysis, and the CARS method is fast enough to give information about the dynamics of the interactions between the hair care agents and the hair. Because of the speed, the researchers aim to quantify how small uncharged molecules used in hair care products - like glycerol, glycine, and water - affect the characteristics of individual hairs. 

Julia Lyubovitsky at the University of California Riverside, US, researches non-destructive optical techniques to investigate biological systems and says the approach taken by Potma and colleagues makes sense. 'The non-destructive CARS method yields a 3D high-contrast view of hair and potentially allows the investigators to track penetration of chemicals into the different areas of the hair,' she says. 'The unique source of this contrast is complementary to other non-destructive non-linear optical imaging methods so it could possibly provide additional information that wasn't previously available about hairs and their response to chemicals.' 

From their analyses so far, Potma and colleagues have found that small uncharged molecules, such the active compound panthenol in some P&G shampoos, glycine, and glycerol, penetrate the hair strands homogeneously and cause the hair to swell and become looser.  

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