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The Treatment of Hyperpigmentation and Facial Dark Spots:
Why Ingredients Such as Hydroquinone, Azelaic Acid, Vitamin C, Kojic Acid, Licorice Extract, Niacinamide, Soy, and Tretinoin May Be Helpful
If you’ve ever developed a dark spot on your skin after an acne breakout, then you know all about post-inflammatory hyperpigmentation (PIH). That’s the medical term for the dark discoloration on your skin that appears after that annoying pimple finally goes away. PIH can also appear after a mosquito bite, a rash, or really any type of skin inflammation.
Why does it occur? Because of melanocytes.
The Science of Hyperpigmentation: The Biochemistry of Melanocytes and the Skin Pigment Melanin
Why do some of us develop dark spots after inflammation or injury to the skin?
These dark spots result from the activity of a particular cell that lives in our skin called a melanocyte.
Melanocytes produce melanin, and too much melanin in one area of the skin can result in dark spots, solar lentigos, post-inflammatory hyperpigmentation, and melasma.
Melanocytes are the cells in your body that help produce melanin, and they're found throughout your skin. Melanin is the pigment in your skin that helps determine your skin tone, and it’s usually distributed pretty evenly over the surface of your skin.
The key factors in determining how much skin pigment you have in your skin are:
The activity of your melanocytes
The type of melanin in your skin
Where that melanin is distributed in your skin
Too much melanin concentrated in one area can produce solar lentigos, also known as sun-induced freckles or dark spots. It can also produce post-inflammatory hyperpigmentation (PIH) after an injury or an insult to the skin in one area. Too much melanin can also produce dark patches over certain areas of the face due to hormone fluctuations, known as melasma.
The Science of Melanocytes, Melanosomes, and Melanin
Melanocytes are the cells that produce melanin. Keratinocytes are the cells that make up the layers of our skin. It's the connection between these two that help determine skin color and skin tone.
Melanocytes make melanin, your skin pigment. (One of the key enzymes in that process is called tyrosinase; you'll hear more about that enzyme in a minute, because it's a key player in the development of effective treatments.)
All of us, no matter our skin tone, have melanocytes scattered throughout our skin. A single melanocyte has long “arms“ called dendrites, and a single melanocyte is able to connect with approximately 36 different keratinocytes via these arms.
That connection matters, because that's how melanocytes transfer melanin to your skin cells.
That melanin is found in small bundles inside the cell called melanosomes. I like to picture melanosomes as tiny little footballs inside the cell. Your melanocyte transfers those tiny little footballs to many different keratinocytes, and that's why you see skin coloration. It might be nice and even (your skin tone) or it might be irregular, resulting in dark spots or patches.
In some situations, your melanocytes start to "activate" and produce more melanin than usual. For example, after exposure to UV radiation, melanocytes start to amp up their melanin production. We call that tanning.
Other signals can trigger more melanin production, such as a rash or a pimple. That can result in PIH: post-inflammatory hyperpigmentation, which are the dark spots or patches that are left on your skin after the inflammation subsides.
Another signal, for some women and fewer men, is a condition called melasma. In this condition, a rise in hormone levels, such as during pregnancy or with oral contraceptives, can trigger dark patches on certain areas of the face such as the forehead, cheeks, and above the lips.
How The Science of Melanin Production Has Led To The Treatment of Hyperpigmentation: The Role of Hydroquinone, Azelaic Acid, Vitamin C, Kojic Acid, Licorice Extract, Niacinamide, and Soy
Learning about the biochemistry behind the process of hyperpigmentation has led us to different treatments that can be effective for some types of pigmentation, in some people.
Hydroquinone: A Tyrosinase Inhibitor
Hydroquinone is a tyrosinase inhibitor. Tyrosinase is the enzyme that converts tyrosine to melanin. One way to block the production of melanin is to block the activity of this enzyme. That's why hydroquinone (HQ) is so effective at treating hyperpigmentation.
Hydroquinone is a small molecule that's able to penetrate the skin effectively.
It is often found in prescription products used to treat hyperpigmentation.
In some places, it's also available OTC.
It's banned in the European Union as a cosmetic additive, so cannot be sold there OTC.
It is available in the United States at an OTC concentration of 2%.
In both countries, it's available as a prescription product, usually at a 4% concentration.
While HQ can be very effective at treating hyperpigmentation, dermatologists are very careful when prescribing it. That's because if it's used at high concentrations, or even if used at low concentrations for long periods of time, it can actually cause darkening of the skin. When I'm prescribing hydroquinone, I always put a time limit on its use.
Other Ingredients That Help Block the Production of Melanin Include Azelaic Acid, Vitamin C, Kojic Acid, and Licorice Extract
Azelaic acid is a prescription product that has also been shown to inhibit the production of melanin. It's often used as a prescription treatment for acne, because it reduces the production of acne lesions while also helping reduce the hyperpigmentation that can result from acne.
Vitamin C is an antioxidant, which helps protect the skin from the damage induced by free radicals. Vitamin C also helps reduce the activity of tyrosinase, thus helping reduce the production of melanin. In clinical studies, it's shown benefit in reducing the development of facial dark spots. For more on the science behind vitamin C in skin care, please see this post.
Kojic acid is available in some OTC products. It's derived from natural sources, and also helps block the production of melanin. While not as effective as the prescription ingredients, it is helpful for some.
Licorice extract is derived from the root of the plant Glycyrria Glabra Linnem. It has several benefits, including the ability to reduce the production of free radicals and anti-inflammatory abilities. It also improves hyperpigmentation by reducing the production of melanin. Again, it has milder effects than prescription products.
Ingredients That Help Improve Hyperpigmentation By Blocking The Transfer of Melanosomes: Niacinamide and Soy
Niacinamide, also known as nicotinamide, is vitamin B3. Topical OTC products containing niacinamide have been helpful in treating the visible signs of skin aging as well as some types of hyperpigmentation. It does this by several methods, one of which is that it interferes with the transfer of melanosomes (the little "football" bundles of melanin) from melanocytes to keratinocytes.
Niacinamide has been studied in multiple clinical trials, which is why it's often used in anti-aging skin care products, typically in conjunction with other ingredients. In one clinical trial, for example, use of a 2% niacinamide gel reduced hyperpigmentation after 4 weeks of use.
Soy extracts also seem to inhibit melanosome transfer. These are, again, often used with other ingredients, but may be helpful in evening out skin tone. In one study, volunteers used a moisturizer with soy extracts for 12 weeks and compared it to just the moisturizer base alone. After 12 weeks, the moisturizer with soy extracts was better at evening out skin tone and blotchiness, along with improving dullness and skin texture.
Ingredients That Help Improve Cell Turnover: The Role of Retinoids
Retinoids, such as prescription tretinoin (brand name Retin-A) have also shown to be helpful in the treatment of hyperpigmentation. That’s one of the reasons why, when I treat a patient with acne who's prone to developing dark spots afterwards, I make sure that tretinoin is one of my treatments. Tretinoin helps reduce hyperpigmentation because it increases cell turnover, and also helps reduce transfer of melanosomes to keratinocytes.