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What's up with hair dyes?

What's up with hair dyes?

Our hair play an important part of our daily lives. Not only does it keep us warm and protect us from the sun, it also serves as a reflection of our mood, a symbol of our heritage, and even a fashion statement. Our article today will focus on hair color and hair dyes, but in order to understand this topic, we will begin with a brief discussion of basic hair biology.

Hair anatomy

The hair has 2 major components, the bulb and the shaft. From out to in, the 3 layers of the shaft are the cuticle, the cortex, and the medulla.

The cuticle is a protective shell that surrounds the inner components of the hair. It is shaped like overlapping scales, like shingles on a roof or the scales on a fish. The cortex consists primarily of keratin, which is the structural protein found in your skin, hair, and nails, and melanin, which is the pigment that gives hair color. The medulla is the innermost layer of the hair.


Growth cycle

While it seems like hair constantly grows without stopping, the hair’s life cycle actually has 3 phases:

  • Anagen phase - This is the growth phase. During this period, hair grows at a rate of 1 cm per month. This phase typically lasts 3-4 years.

  • Catagen phase - This is the transition phase. During this period, hair growth slows down in preparation for the final phase. Typically, this lasts 2-3 weeks.

  • Telogen - This is the rest phase where the hair completely stops growing. This phase lasts about 3 months.

**Today’s discussion will only include a brief summary of the growth cycle. We will discuss this in more detail at a later article where we talk about hair loss.

Hair color

People around the world have all sorts of natural hair colors, including red, blonde, brown, and black. These colors result from a natural blend of 4 ingredients: pheomelanin (red), brown eumelanin, black eumelanin, and keratin (white-yellow). Your hair color essentially depends on the concentration of each component.

Hair dyes

Phew, we covered a lot of hair biology already. Now that we have a general understanding, let’s talk about how hair dyes work. To start, it’s important to understand that there are 5 major types of hair coloring: bleaching, permanent, demi-permanent, semi-permanent, and transient.



This is exactly as it sounds, you add bleach to the hair. Sodium hypochlorite, the main ingredient in bleach, does the same thing to your hair as it does to your clothes, it removes color. By penetrating the cuticle and going directly into the cortex, it can oxidize the melanin in your hair, leaving you with a color that reflects the natural color of keratin, which is a whitish yellow.

Permanent hair coloring:

While bleaching is a straightforward chemical process, it is both damaging and difficult to control. As consumers typically demand specific colors using minimally damaging dyes from their hair stylists, chemists are constantly challenged to produce safer and more effective dyes. In general, these dyes work using a 4-step process.

Step 1 - Opening the cuticle

While bleach easily penetrates the cuticle, most dyes are unable to do so. Hence, the first step in the process is to open the cuticle. This can be done by creating an alkaline environment, typically using ammonia, which opens the scales creating a porous surface (think about it like a closed vs open pine cone).

Step 2 - Remove the innate color

In order to achieve certain colors, especially unnatural ones like pink or neon green, it is essential to remove the innate color. Just like in the case of bleach, this can be done by using an oxidizing agent such as hydrogen peroxide. It reacts with melanin and lightens the natural hair color. These ingredients are called developers and their strengths are measured in volumes ranging from 10 to 40. A volume of 10 means that 1 mL of your developer will release 10 mL of oxygen molecules. These molecules are important for both oxidizing melanin and for activating your hair dye. For reference, bleach is a 40 volume developer. The higher this number, the more effective it is at removing color but the more damaging it is to your hair.

Step 3 - Apply the desired color

After the first 2 steps, the desired hair color can finally be applied. In addition to the aforementioned functions, both the alkaline and the oxidizing agents have an additional effect in that they create an environment where the hair dye will undergo chemical conversion to its colored form. This is why when you look at hair dye before it is applied, the color can sometimes look nothing like what it is supposed to. After penetrating the opened cuticle, the hair dye binds to proteins in the cortex.

Step 4 - Close the cuticle

Now that the color has been successfully applied, the cuticle can be closed to preserve the quality of the hair and to trap the dye within using creams, shampoos, conditioners, or other products.

Demi-permanent and semi-permanent hair coloring

The primary difference between these and permanent hair coloring is that these processes do not use ammonia. While demi-permanent uses a lower volume developer, semi-permanent does not use developers at all. As expected neither one of these colors are long lasting and will mostly fade with sufficient washes.


Transient hair coloring

These are special hair dyes that are meant for one time use and will fade with 1 or 2 washes. You can pretty much think of these as adding surface color to your hair as the dye just sticks onto the cuticle until you wash it out.

Does hair dye cause lasting damage?

Many consumers are concerned that putting chemicals such as hair dyes on their scalp may cause permanent hair damage or hair loss. It’s a reasonable concern if you think about it because hair dyes are strong enough that they pretty much alter your natural anatomy. However, rest assured. In general and for most people, while there is no question that hair dyes cause at least some degree of immediate hair damage, there isn’t much scientific evidence that supports permanent hair damage or hair loss with use of conventional hair dyes. The exception is for individuals with allergies to common ingredients in hair dyes, such as PPDs (paraphenylendiamines). In these cases, consumers may experience a skin reaction called allergic contact dermatitis where they can have a rash and occasionally hair loss after their scalp comes into contact with the allergen. While these reactions can have medical and cosmetic significance, they are not very common.


Let’s sum it up!

Hair is a fascinating topic where art and science often go hand-in-hand. While our hair offers a forgiving canvas for us to show the world our personalities and our styles, it is also important to keep it healthy to prevent hair loss, but that will be a topic for another day.

That's all for today folks!


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