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Expanding the Frontiers of nail product evaluation: novel application of differential scanning calorimetry (DSC) for assessing crosslinking density and predicting nail brittleness and flexibility.
Authors
E. Malinauskyte, K. Mateo, V. Castro-Haly, L. London, N. Parikh, X. Tu (Int. J. Cos. Sci., 2024, 00: 1 – 16, the original paper, and TRI Library entry.
Nail treatments and enhancement have fast become a mainstay of the beauty industry, with rapid industrial growth seen over the past decade. Many consumers now attend professional salons for manicures or pedicures, with numerous products including acrylic extensions, UV-cured varnish and nail builders designed to address common consumer complaints, such as weak or brittle nails. While claim substantiation is well-established for many personal care and beauty products, for nail-based products it is much less developed, leaving consumers have no choice but to rely on largely unproven product claims.
TRI Princeton teamed-up with OPI to investigate whether differential scanning calorimetry (DSC) could be used as a tool to assess crosslink density within nail keratin, as well as predict nail brittleness and flexibility. This work largely confirmed that nail-hardening treatments increased the amount of cross-linking within the keratin structure (characterized by an increase in denaturation temperature), and nail softening treatments led to a reduction in cross-linking of keratin in the nails (characterized by a decrease in denaturation temperature). An increase in cross-linking caused nails to become harder and reduced flexibility, whereas a decrease in cross-linking increased nail flexibility and reduced the incidence of nail bending fatigue. Incidentally, nail clippings from panelists who admitted to using nail salon services tended to have a higher denaturation temperature, which may be because certain nail polishes, basecoats, undercoats, artificial nails, and related products contain formaldehyde, a nail hardening treatment, that alters nail crosslinking density and nail flexibility significantly.
In addition, the impact of humidity and hydration, as well as commonly encountered cleaning agents, upon keratin cross-linking and flexibility were also investigated. Nail flexibility was significantly impacted by humidity, with 80% RH leading to 10-fold higher resistance to breakage when compared with 40% RH. Exposing nails to Clorox, hydrogen peroxide or ammonia solution, commonly found in household cleaning items (albeit it much lower concentrations), led to changes in keratin cross-linking and flexibility. Both Clorox and hydrogen peroxide were suspected to chemically change the nail permanently, possibly through oxidation of disulfide bridges to cysteic acid residues, leading to a change in behaviors, but ammonia was temporary and simple treatment with water reversed the effects.
To summarize:
Nail hydration is key – more hydrated nails resist breakage more readily.
Nails with more cross-linked keratin, have reduced plasticity and flex which can cause them to break more easily.
Nail hardening treatments increased the amount of cross-linking present, whereas with nail softening treatments the opposite was true.
Household items such as bleach (Clorox) and hydrogen peroxide can chemically change the nail, leading to weakness, but with ammonia-based items any changes were reversible.
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