Unit II: The Role of Acids and Bases and Chemical Reactions in Hair Dyes

If you have ever dyed your hair, you know that it is important to carefully read the labels and instructions properly in order to complete the hair dying task properly. However, if you have read the ingredients label, it is certain that you have come across some acids and bases. Some might believe that it seems odd for hair products to contain such corrosive substances. In reality, the acids and bases are the substances that get the job done!

In order to understand how the acids and bases carry out the dyeing process, it’s important to comprehend the structure of hair. The cuticle is the outer layer of the hair. Although it cannot be seen by the naked human eye, it resembles scales on a snake or shingles on a roof when examined under a microscope. Its purpose is to protect the inner component of hair and allow chemicals to pass through, which will be explained thoroughly later on. Inside the cuticle is the cortex, which acts as a control center for the hair. When dyeing hair, the chemical must enter the cortex in order for the process to be effective.

The Role of Acids and Bases

Hair dye usually requires several different substances. One of the substances in primarily composed of a base. The properties of a base allow it to be able to open the cuticle, allowing bleach to enter the cortex. The dye reacts with the cortex (found inside the cuticle) in order to remove the original colour of the hair. For example, ammonia (NH3) is often used for this reaction. Its pH of 11.6 makes it a basic substance, which is explains its efficiency to be able to open the hair cuticle and allow the colour to absorb. Afterwards, it is crucial that the cuticle closes, to prevent any damage from occurring. This is usually the last step of the hair dyeing process, once the dye comes in contact with the cortex. The properties of acids allow it to have the ability to close the cuticles of hair. Its job when closing the cuticle, is to leave hair healthy, shiny and full of strength. A common acid used in this case is hydrochloric acid. Since it is not pure hydrochloric acid that is being applied to the hair, it is not as corrosive as it seems. The application of an acid is crucial in the hair dyeing process because if not done properly, the cuticle of the hair would be left open.This can cause hair to become brittle and untangled, irritated and can lead to hair loss. Keep in mind, that the pH levels of hair should remain between 3.5 and 9.5. Going beyond or below these numbers can cause severe damage, which explains why applying hair dye to hair is not ideal to preserve the health and strength of hair. The common acids and bases used in the hair dyeing process have a pH level that is either below or above 3.5 and 9.5. The most effective way to eliminate some of the dangers of dyeing hair is to use shampoo. If at any point the pH level of hair is too high or too low, some shampoos would be able to neutralize it. Most shampoos have a pH of 4.5 to 5.5, which is why it can neutralize the hair to ensure to that its pH is in between 3.5 and 9.5.

Mineral Dyes

A common chemical found in mineral dyes are lead acetate. As of today, there are strict regulations on the use of lead in hair as it is toxic. Either they are banned in some countries or are used in small concentrations. When it comes in contact with the hair, a complex chemical reaction occurs with lead acetate and keratin, as the molecular formula of keratin is C28H48N2O32S4. One of the products is lead sulfide, which turns out to be insoluble (forms a precipitate). That product then gets absorbed into the scalp, which does no damage because the lead has low concentrations. Another chemical reaction that occurs with hair and mineral dyes is with silver nitrate and keratin. The silver nitrate is crucial, as it changes the colour of the hair. When it comes in contact with keratin, an insoluble silver sulfide compound is produced (formation of a precipitate). Instead of being absorbed back into the scalp, it remains in the cortex of the hair. This is using metals in hair dyes is long lasting. As new hair grows, hair dye has to be applied once more as there would be no silver nitrate in the new grown hair.

It is common knowledge that several applications of hair dye can do permanent damage. Based off of reading this post, what is the reason that hair dyes do so much damage? What changes could be made to the chemical composition of hair dye to prevent this damage?

Bibliography

Helmenstine, A. M., & H. (n.d.). The Science of How Hair Color Works. Retrieved November 06, 2018, from https://www.thoughtco.com/salon-hair-color-chemistry-602183

Landsdown, A. B. (n.d.). Hair Dyes and Hair Treatments. Hair Dyes and Hair Treatments. Retrieved November 06, 2018, from http://www.chemistryexplained.com/Ge-Hy/Hair-Dyes-and-Hair-Treatments.html

PH for Hair Color. (2011, May 07). Retrieved November 06, 2018, from https://www.simplyorganicbeauty.com/ammonia-free/online-salon-educatio/ph-for-hair-color/

Price, R. (2016, August 19). Hair Cuticle 101 – The Most Important Part of Your Hair. Retrieved November 05, 2018, from https://www.howtomakeyourhairgrowfastertips.com/hair-cuticle-101-the-most-important-part-of-your-hair/