Updated: Oct 5
The pH effect on the bleached hair was presented by Dr. Ernesta Malinauskyte during the Hair S’19 Conference, organized by DWI in September of 2019. We have received many requests to share our findings by attendees of the conference, as well as those who attended our seminar held at TRI at the end of 2019. Unfortunately, we were not able to share the unpublished information...until now!
We would like to introduce a joint publication by Lonza and TRI titled “Effect of equilibrium pH on the structure and properties of bleach-damaged human hair fibers” (https://library.triprinceton.org/1erqg3t/ ). This published research paves a foundation for soaking experiments of bleached hair. A lot of scientists seem to struggle to explain certain effects of treatments because there is more than one variable involved. We have begun dissecting this issue by experimenting with clean 3x 9% liquid bleached hair (Figure 1B), which is a model substrate in damage repair studies. Although such levels of bleaching sound terrifying to some people, it really is not. If you look at image B, this is considered to be half-way stage between medium brown European virgin hair (Figure 1A) and hair that is bleached to the level of “platinum” (Figure 1C). Thus, damage levels are reasonable and can represent “real life”.
During this study, we exposed hair to different pH solutions that were composed only of water, sodium hydroxide and hydrochloric acid for 24 h. Minimal composition together with only low molecular sizes of molecules ensured a decent penetration profile and moreover, the possibility to attribute the observed effects to hydrogen or hydroxide ion concentration, or in other words, pH.
The main findings suggest that:
pH does not affect tensile breakage within the region of 3-10.
Under highly acidic conditions (equilibrium pH~3), the glutamic & aspartic acid side chains of the hair proteins protonate, making the hair less hydrophilic and more compact.
In turn, this makes “bad hair days” on humid days less of an issue because hair absorbs less water, is more flexible in dry conditions and less “mushy” in wet conditions. Unfortunately, it also reduces the diameter of the hair fiber and possibly the penetration levels of hydrophilic nutrients including those that are claimed to enrich hair.
Slightly acidic conditions (equilibrium pH~5) allow the formation of the best structural integrity and makes hair the stiffest in dry conditions.
Under alkaline conditions (equilibrium pH ~10), the hair swells, opening themselves for water and possibly other actives to penetrate, but otherwise not practical for bleached hair owners.
The choice of pH conditions can simply depend on your research and/or marketing goal, or what you want to achieve at home!
For more information about hair and skin science visit us at www.triprinceton.org
Read the full paper at https://library.triprinceton.org/1erqg3t/