Article by: Perry Romanowski

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.


  1. Avatar
    Courtney R

    What would cause a clients red hair to turn dark brown when lightener/bleach was placed on it? (After several minutes it began to lighten)

    1. Avatar
      Perry Romanowski

      I don’t really know but I suspect that it was a combination of the hair getting wet (this tends to make the hair look darker, and maybe the lightener bleached out the lighter shades of melanin before it affected the darker shades.

  2. Avatar

    Are all of these reactions permanent?

    1. Avatar
      Perry Romanowski

      No reaction is permanent but yes, they are all impractically difficult to reverse.

  3. Avatar
    karush gia

    what is the structural equation for depilatories?

    1. Avatar
      Perry Romanowski

      I don’t know what you mean by “structural equation”

      1. Avatar
        karush gia

        i was just wondering if you were to draw the equation written in the depilatories section, what would it look like?

        1. Avatar
          Perry Romanowski

          It would be something like this…

          2 HSCH2CO2H (thioglycolic acid) + R-S-S-R (cystine) → HO2CCH2-S-S-CH2CO2H (dithiodiglycolic acid) + 2 RSH (cysteine)

  4. Avatar

    Is there a major difference in boxed dyes vs the expensive professional stuff? If so, what is it? Would you say box dyes will ruin hair in comparison to professional stuff?

    1. Avatar
      Perry Romanowski

      There isn’t really a difference chemically. But you get better results when a professional colors your hair. This is one cosmetic where skill does make a different.

  5. Avatar

    Can amino acids relax hair?

    1. Avatar
      Perry Romanowski


  6. Avatar

    Can i know the acids or other components which break down hair bonds in safe hair keratin products
    I know formaline,glyoxylic, NaOH and the one you refer to it

    1. Avatar
      Perry Romanowski

      Hair keratin products do not break down hair bonds. They form hair bonds.

  7. Avatar

    can ammonia thioglycolate be used to make soap?

    1. Avatar
      Perry Romanowski

      Probably not a soap anyone would want to use.

  8. Avatar
    Maria S.

    I want to bleach my hair, but someone close to me has multiple chemical sensitivity, so I am wondering, for how long will the chemicals affect him? Will it be for as long as my hair is bleached, or will it just affect him in the beginning? Thank you so much for your help 🙂

    1. Avatar
      Perry Romanowski

      If the bleaching is done properly there should not be any residual chemicals that will affect the person close to you.

  9. Avatar
    Maya Smith

    Do you know if there is a chemical equation that could express how hair denatures or burns when exposed to heat? Or how to chemically explain the relationship between hair and heat like straighteners

  10. Avatar

    Can u describe the chemical reaction which creates tinting effect

    1. Avatar
      Perry Romanowski

      What type of tinting effect do you mean?

  11. Avatar
    Nahar Singh

    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.

    1. Avatar
      Perry Romanowski

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

  12. Avatar
    Lynda Scott

    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!!!

    1. Avatar
      Perry Romanowski

      Sorry, only a doctor can answer that.

  13. Avatar

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

    1. Avatar
      Perry Romanowski

      No, I don’t have that information.

  14. Avatar

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

  15. Avatar

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

  16. Avatar

    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.

    1. Avatar

      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.

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  18. Avatar

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

    1. Avatar
      Perry Romanowski

      The reactions are in the post above.

  19. Avatar

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

    1. Avatar
      Perry Romanowski

      Maybe in a future post.

  20. Avatar

    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?

  21. Avatar

    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 ?

    1. Avatar
      Perry Romanowski

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

  22. Avatar

    Never using bleach again…..

  23. Avatar

    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

    1. Avatar
      Perry Romanowski

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

  24. Avatar

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

    1. Avatar
      Perry Romanowski

      Great point!

  25. Avatar

    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?


    1. Avatar
      Perry Romanowski

      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.

      1. Avatar

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

  26. Avatar

    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?

    1. Avatar
      Perry Romanowski

      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.

  27. Avatar

    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.

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  29. Avatar
    Kerrie cook

    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?

    1. Avatar
      Perry Romanowski

      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.

  30. Avatar

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

    1. Avatar
      Perry Romanowski

      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.

  31. Avatar
    Junoh Kim

    Good summary!

  32. Avatar


  33. Avatar
    devil zapperz,.!

    its great stuff

  34. Avatar

    very helpful

  35. Avatar
    sars simp

    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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