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Chemical Reactions in Cosmetic Science

In college, most chemistry classes were focused on creating chemical reactions. We were constantly challenged to figure out what reaction would happen when you mix chemicals together.

Cosmetic science is not usually reactive

So, you might find it surprising that cosmetic scientists usually do the opposite. We mix chemicals together and hope that nothing happens. In a cosmetic formula, chemical reactions are bad. They are a sign of instability and we do everything we can to prevent them.

This drive to make nonreactive systems might lead you to wonder whether all those chemical reactions you memorized in Organic Chemistry were a waste of time. And if you work as a cosmetic formulator, you might wonder, “Are there any chemical reactions in cosmetic science?”

Yes, there is!

Reactive cosmetic products

While most of the chemical reactions in our industry occur at the raw material suppliers labs, there are some cosmetic products specifically designed to chemically react.  Here’s a list of the most common.

Permanent Waves

These products are designed to permanently change the shape of hair. People with straight hair often use permanent waves to get a little curl in their hair. A permanent wave formula has a reducing agent like thioglycolic acid that reacts with the di-sulfur bonds in the cystine amino acids breaking down the hair structure. Hair is first shaped into curlers, then the product is put on hair. It begins reducing hair and is rinsed with water to stop the reaction. A neutralizing chemical like hydrogen peroxide, is added which reforms the di-sulfur bonds into the new configuration.

Hair Relaxers

These products do the opposite of permanent waves. They make curly hair permanently straight. The method is similar you chemically break down hair, reshape it, then reform the protein bonds in the new configuration. Sometimes ammonium thioglycolate is used but most often it is sodium hydroxide or lithium hydroxide. The compounds break down the di-sulfur bonds in hair and the neutralizing step stops the reaction.

This is the most damaging chemical treatment for hair.

Hair Bleach

Hair bleaching is a process used to turn brunettes into blonds. You didn’t really think that there were that many blonds in the world did you? Hair bleach is a chemical reaction between melanin (the material in hair that gives it color) and hydrogen peroxide.

Hair Colors

Hair coloring is a slightly more complicated version of hair bleach. It uses hydrogen peroxide to break down hair’s natural color, then the peroxide also oxidizes a polymeric reaction with dye monomers. When the dye polymerizes inside the hair, it creates a color molecule that is too big to easily come back out.

Skin Darkening

These products are designed to give fair-skinned people a tanned look. They work by using an ingredient called dihydroxyacetone or DHA. It reacts with the proteins in the stratum corneum via the Maillard reaction to produce the brown (although sometimes orange) color. All the steps haven’t been worked out, but basically when DHA is exposed to skin protein, it is converted to pyruvaldehyde, which then reacts with arginine, lysine, and histidine amino acids in skin to form brown/yellow pigments called melanoidins.

Be sure to see Kelly’s article about DHA in Cosmetics & Toiletries magazine.


These are products designed to help people to remove unwanted hair. The primary active in these types of cosmetics is some version of thioglycolic acid. The acid reacts with the cystine amino acids in hair and breaks down the S-S linkages. The hair is reduced to a jelly like mass that can then be wiped away. Note this is the same reaction as in permanent waves.

2SH-CH2-COOH(thioglycolic acid) +R-S-S-R(cystine)—–> 2R-SH + COOH CH2 SS CH2 COOH (dithiodiglycolic acid)

Chemical reactions are not the primary focus of most cosmetics, but there are a few reactions so don’t fret. Memorizing those reactions in Organic Chemistry wasn’t a complete waste of time.

{ 45 comments… add one }
  • kadeine 02/06/2016, 4:59 pm

    Can u describe the chemical reaction which creates tinting effect

    • Perry Romanowski 02/08/2016, 8:33 pm

      What type of tinting effect do you mean?

  • Nahar Singh 02/04/2016, 11:18 am

    When we use silver nitrate on skin it get removed by acetone and other solvents within two three minutes. How we can fix color of silver nitrate on human skin immediately or how it will reappear with few minutes.

    • Perry Romanowski 02/04/2016, 3:59 pm

      I do not know. That doesn’t sound like a cosmetic product.

  • Lynda Scott 11/06/2015, 8:46 am

    Thanks for all the information!! I am in a dilemma right now I am a chemical reaction to something that was applied to my hair last night. I think it was the rinse since the same thing happened to me about a year ago and I had to go to the doctor. I thought it was getting better. I am sure what is causing this reaction.
    Any idea HEEELLPP!!!

    • Perry Romanowski 11/11/2015, 8:04 am

      Sorry, only a doctor can answer that.

  • Jennifer 10/27/2015, 1:09 am

    Do you know the associated hazards (WHMIS and MSDS regulations), including hazards associated with the handling and disposal of chemicals?

    • Perry Romanowski 10/27/2015, 2:44 pm

      No, I don’t have that information.

  • Dani 10/10/2015, 11:22 am

    Do you know what chemical will neutralize, eliminate or wash away sulfer?

  • freen 10/04/2015, 6:17 am

    What’s the chemical equation for the reaction between hair and ammonia? like what happens the detailed steps?

  • Jessica 08/29/2015, 9:55 am

    Hi! I wanted to know what would cause someone’s hair to make popping noises when putting lighter on it. I’ve been doing hair for 8 years and have never heard this before till just recently. I was trying to just break with base up with lightener then put a level 6v on it. Even when I put the color on it turned foamy.

    • Perry Romanowski 08/31/2015, 3:16 pm

      I don’t know and there isn’t enough information for me to even guess. I’d suggest you put this question in our forum. http://chemistscorner.com/cosmeticsciencetalk

    • Justine 12/04/2015, 7:49 am

      From my experience this is probably because the person has used metallic salt dyes on their hair. Most of the brands that claim to “gradually” color the hair contain metallic salts such as copper, silver or lead. The “boiling, popping and foul smell” results from the chemical reaction between copper, ammonia and peroxide- though I can’t tell you exactly what that reaction is, it can be very damaging to the hair from what I have seen. Unfortunately, there is no way to remove metallic dyes from the hair- they simply have to be grown out and cut off.

  • Aakash 06/15/2015, 2:30 am

    i want examples of chemical reactions taking place in industries……plz…i could not find anywhere on the net!

    • Perry Romanowski 06/17/2015, 10:06 pm

      The reactions are in the post above.

  • jane 12/27/2014, 10:13 am

    Do ou mind showing the chemical reaction for depilatories not just the molecular formulas. Who attacks what ???

    • Perry Romanowski 12/31/2014, 9:15 am

      Maybe in a future post.

  • Hanna 12/06/2014, 10:04 pm

    I would like to make my own professional hair color line but I don’t know how to start it. Where to go. I was looking for a lab but I can not find any which can help me with it. Should I ask a chemist to help me with that? Do you maybe have some advice?

  • Tyler 12/03/2014, 7:53 am

    I’m experiencing scalp sensitivity from chemicals in a dye that I applied about 3 weeks ago. My doctor says the chemicals are still in my hair. Is it possible that the chemicals could be still causing my scalp irritation? If so, what could I do to neutralize ?

    • Perry Romanowski 12/07/2014, 10:41 am

      If you’ve washed your hair I doubt that the chemicals are still in your hair.

  • Emmalee 10/14/2014, 12:45 pm

    Never using bleach again…..

  • Heather 09/25/2014, 3:37 pm

    I have done hair for 10 years and have done many of colors. Just recently I have moved salons and snide being in the salon have had more trouble with my bleach getting soooo hot you can’t even touch the foils (without the dryer in a matter of mins) I have never had this problem before so I am wondering if it could be something in the water maybe piping? At this shop that could be causing it. If so they are not shampooed first so would the color brushes be able to be the factor (since we wash them in the water) that is causing the reaction

    • Perry Romanowski 09/29/2014, 7:20 pm

      It sounds like there is something in the water. Try using different water and see if you get the same result.

  • Bob 08/25/2014, 8:58 pm

    There’s another chemical reaction, saponification, which always used to make soap based facial or body cleanser.

    • Perry Romanowski 08/26/2014, 7:57 am

      Great point!

  • Stacy 07/24/2014, 9:57 am

    Why would hair bleach cause hair to literally almost burn to the touch?!

    I’ve never had this reaction while using bleach on a client in 15 years, but today a client’s hair was so hot it nearly burned my hands. Is there a chemical explanation for this?


    • Perry Romanowski 07/30/2014, 1:34 pm

      I do not know but the reduction of hair protein using bleach is an exothermic reaction so there must have been a lot of bond breaking going on.

      • Sarah 09/10/2014, 10:33 pm

        Most likely the client had box dye on the hair, which has metallic dyes in it which are nearly impossible to remove.

  • Flo 06/10/2014, 1:41 pm

    Could you please explain what happens when we overprocess the hair. Let’s say we use a persulphate based bleach with 12% peroxyde on pre-bleached hair. That hair becomes like a gel. What is that, and what happens to the proteins in the hair?

    • Perry Romanowski 06/11/2014, 5:04 pm

      Great question. What happens is you reduce the S-S bonds that give the hair protein its structure so much that the protein strands become fluid and gel like. Imagine that hair is like a cargo net. The bleach is like scissors that cut the links between each strand of the net. If you cut too many strands you’ll end up with a bunch of hanging strands that don’t work as a single unit.

  • Kristin 02/14/2014, 11:23 pm

    Kerrie does the client have hard water at home? I’m not positive but I think the sulfur or copper deposits from hard water can react with the bleach and can cause excessive heat and uneven results.

  • Kerrie cook 10/21/2013, 12:30 am

    I would like to know why is there a chemical reaction.
    a client that has prolonged use of a shampoo and conditioner with a silicone base ( silicone build up)
    has foils with a powder bleach and 20 vol peroxide
    chemical reaction
    consistency of the powderlightner changes expands the foils and increases in heat. Starts to breakdown the hair shaft
    What is the chemical reaction called?
    What is the silicone name?
    is it only with non dissolvable silicones?

    • Perry Romanowski 10/22/2013, 12:11 pm

      The silicones are unlikely involved. 20 vol peroxide will break down hair whether there is silicone present or not. You just can’t leave it on as long as usual.

  • AJL 03/18/2013, 2:46 am

    Can you name any chemicals in cosmetics that are examples of the cocktail or combination effect?

    • Perry Romanowski 03/18/2013, 12:21 pm

      This is a very complicated question and there is not currently any evidence that ingredients used in cosmetics have any sort of cocktail or combination effect.

  • Junoh Kim 02/25/2013, 5:44 pm

    Good summary!

  • HazelBrown-Eyes 08/12/2011, 6:33 am


  • devil zapperz,.! 04/25/2011, 3:57 am

    its great stuff

  • pinky 01/15/2011, 2:35 am

    very helpful

  • sars simp 11/15/2010, 9:56 am

    this is awsome!! you guys helped me so much with this paper i am writing for chemistry of cosmetics. i searched evrywhere and couldnt find anything until i got to your site. Thanks again :)

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