Why do brows turn red?

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"Why do brows from certain treatments develop a reddish tint over time? The answer lies in the biochemistry of iron oxide and its interactions with ferritin, a protein produced by our bodies. These interactions can change the iron's oxidation state, leading to the undesirable reddish color. However, there's a silver lining – this issue can be effectively addressed at the molecular level. By intelligently modifying the iron oxide molecules in our pigments, we can prevent these unwanted color changes and maintain the intended brow shade."

1. Background

The issue of pigments, especially in eyebrows, developing a red tint is a common concern among PMU artists. Understanding the reasons behind this and identifying prevention methods might seem challenging, but clarity is possible with in-depth knowledge. This article compiles insights from discussions with 46 experienced PMU artists and incorporates research from the Powderbrows.com Research Center from 2019 to 2023, including ongoing studies. Contributions from 32 artists from the EU, nine from the UK, and five from the US enrich this analysis. It also includes insights from two chemists, a dermatologist, and a physics specialist in optometry to ensure a thorough understanding of the data.

While there's general agreement among artists on the statements' validity, it's important to note that even seasoned professionals may misunderstand how pigments behave in the skin. This article aims to clarify the causes of reddish hues in semi-permanent brow pigments and provide actionable advice for practitioners.

2. "Blue" and "Red" Problems

"Blue" - Often a Problem of Quantity

Understanding why eyebrows might turn reddish is crucial, but it's equally important to distinguish this from the issue of eyebrows turning blue. The latter is primarily a matter of molecular quantity. A high concentration of carbon molecules in the dermis can change how light is absorbed and reflected, causing brows to appear blue. Essentially, it's about the volume of molecules present.

"Red" - Often a Problem of Quality

Conversely, when eyebrows start to look "red," the issue is fundamentally different. This change is due to a molecular-level transformation in the iron oxides used as pigments. The transformation results from interaction with ferritin, a protein the body produces when introducing pigment. This interaction changes the oxidation state of the iron oxides, leading to the color shift observed.

3. From Bottle to Red in Brows

To fully comprehend the transition from applying pigment to the development of a reddish hue in brows, we'll examine the following stages:

Introduction of Iron Oxide Pigment Particles into the Skin

We will explore how the semi-permanent makeup procedure initially introduces iron oxide pigment particles into the skin layers. Immune System Response to Pigment Particles

This will be broken down into three sub-points to discuss the immune system's reaction to the introduced pigments. Macrophage Involvement: We will discuss how some pigment particles are engulfed by macrophages, a type of white blood cell, through phagocytosis.

Fibroblast Encapsulation: We will describe how fibroblasts within the skin encapsulate another portion of pigment particles.
Extracellular Matrix Entrapment: We will explain how some pigment particles become trapped in the skin's extracellular matrix.

Ferritin and Iron Oxide Interactions

We will explore the interaction between ferritin, a protein that stores and releases iron, and the iron oxide molecules in the pigment. We'll highlight how this interaction alters the oxidation state of the iron oxide, leading to the reflection of reddish or "rusted" light, causing the brows to appear reddish.

4. Iron Oxides

Introduction of Iron Oxide Pigment Particles into the Skin

Iron oxide pigments are inorganic, often termed mineral or hybrid pigments. It's vital to distinguish these from organic pigments, which are carbon-based and exhibit different properties and reactions in the skin.

Composition of the Pigment

The final pigment product contains a liquid carrier or cosmetic base stabilizing the colorant. This carrier is a complex mix of solubles, binders, additives, and stabilizers, where the colorant provides the pigment's color, being either organic or inorganic. For inorganic (mineral or hybrid) pigments, common iron oxides include.

CI 77499 - Black Iron Oxides (Ferrous Black) or Iron (II) oxide
CI 77491 - Red Iron Oxides (Ferrous Red)
CI 77492 - Yellow Iron Oxides (Ferrous Yellow)

Specific Iron Oxides: Fe2O3 and Fe3O4

Focusing on iron oxides that contribute to a reddish hue, we consider Fe2O3 (Hematite) and Fe3O4 (Magnetite)

Fe2O3 (Hematite): Often linked to red and brown colors, this iron oxide has a strong potential to cause a reddish hue in semi-permanent makeup.
Fe3O4 (Magnetite): Typically black or brownish-black, it may not directly contribute to a reddish hue but can darken the pigment's overall color, potentially affecting the shade over time.

5. Immune System Response

Macrophages and Phagocytosis

The body's innate defense mechanisms emerge when semi-permanent makeup pigment is introduced, treating it as a foreign entity. Non-specific immune cells rush to the site, including macrophages, histiocytes, and neutrophils. Macrophages, capable of consuming particles up to 10 micrometers, engulf common pigment particles about 500 nm in diameter through phagocytosis. Some macrophages die and become permanent pigment holders within the dermal layer.

Specialized Immunity

As the immune response evolves, specific immunity with T-lymphocytes and B-lymphocytes plays a role. T-lymphocytes target and destroy cells with foreign antigens, while B-lymphocytes might produce antibodies to neutralize the pigment, although this is less common in semi-permanent makeup.

Pigment in the Lymphatic System

Some pigment particles end up in the lymph nodes, where they typically remain indefinitely, as lymph nodes can't expel or break down these materials. This is why ink particles are sometimes found during autopsies.

Note on Macrophage Lifespan

Macrophages have varying lifespans, from days to months, influenced by the tissue environment and activation state. However, they are continually regenerated from bone marrow precursors, maintaining a dynamic but persistent role in pigment retention.

Transfer to the Lymphatic System

Some believe that iron oxide particles are transferred to lymph vessels, especially when one macrophage dies and releases the particle, and another isn't immediately ready to engulf it. This removal process contributes to the persistence of pigment in the skin, which depends on its chemical composition and the immune system's intricate workings.

Pigment Encapsulated in Fibroblasts

After application, pigment molecules cluster and are gradually surrounded by fibroblasts, which transform into myofibroblasts during the skin's healing response. These cells move toward the pigment, secreting structural proteins like collagen to form a fibrotic capsule, isolating and protecting the pigment. However, this encapsulation can remodel over time, affecting the pigment's appearance.

Pigment Stabilization in the Extracellular Matrix (ECM)

Pigment particles also settle into the skin's ECM, a complex structure supporting and sometimes ensnaring the pigment through physical adsorption, mechanical interlocking, and biochemical anchoring. After pigmentation, the ECM might increase its matrix around the pigment, enhancing stability and resistance to the immune response. These processes contribute to the pigment's longevity and stability in the skin.

6. Ferritin and Iron Oxide Interactions

Iron oxides, particularly Fe2O3 and Fe3O4, are known for their stability as colorants in semi-permanent pigments. However, they can turn rusty, causing eyebrows to adopt a reddish hue. Ferritin, a protein that binds to iron and other metals, plays a significant role in this color change.

What Happens to Iron Oxide Particles in the Skin

When iron oxide pigments are introduced into the skin, they undergo various biochemical and physicochemical reactions, potentially leading to color changes over time. Under certain conditions, even stable iron oxides like Fe2O3 (hematite) and Fe3O4 (magnetite) can experience oxidation or other reactions, altering the pigment's color stability.

Understanding Ferritin

Ferritin acts like a biological magnet for iron ions, catalyzing reactions that can degrade iron oxide pigments, leading to a reddish or rusty appearance. The longer the pigment stays in the skin, the more it's exposed to ferritin's activity, increasing the likelihood of this transformation.

Iron Storage and Degradation

Ferritin stores iron in a non-toxic form and safely deposits it. However, when it aggregates, it transforms into hemosiderin, a toxic form of iron. Ferritin's structure is a complex nanocage composed of 24 protein subunits, capable of storing about 4500 iron (Fe3+) ions. Iron ions form crystallites with phosphate and hydroxide ions, creating a compound similar to ferrihydrite.

Factors Contributing to Oxidation

The skin is a dynamic environment rich in biological molecules, enzymes, and cells. Ferritin's interaction with iron ions can catalyze oxidation reactions. External factors like UV exposure and internal factors such as the skin's pH and enzymatic activity can influence this oxidation process, contributing to the pigment's color change over time.

7. Solutions to Red Brows

Silica and Stabilizing Iron Oxide Pigments

Chemists have explored modifying iron oxide molecules to mitigate the interaction of iron oxide molecules with ferritin and similar agents that cause oxidation changes. Combining mineral iron oxide with organic polymetal silica creates a protective "coating" that functions as a barrier.

Initial Solution

Initially developed for industrial coatings to protect metals from environmental degradation, semi-permanent makeup experts adopted this coating technique. The silica coating acts as a shield, preventing the iron oxide from reacting with ferritin, thereby reducing the risk of the pigment turning red after application.

Creation of "Protective Coating"

This protective coating is formed by fusing mineral iron oxide molecules with organic polymetal silica. In industrial applications, coatings using tetraethoxysilane (TEOS) and mercaptopropyltrimethoxysilane (MPTMS) were used to modify the surface of iron oxide magnetic nanoparticles. These silica-based coatings were extensively characterized, providing stability against environmental factors and high temperatures. Adapted for semi-permanent makeup, this silica coating acts as a barrier, preventing the iron oxide from reacting with ferritin and neutralizing the risk of pigments turning red post-application.

8. Silanization

Overview of Silanization

Silanization is a surface modification technique in materials science used to enhance iron oxide's chemical stability and functional properties by fusing it with organic polymetal silica.

Preparation of Silane Coupling Agents

Silane coupling agents, like Tetraethoxysilane (TEOS) and mercaptopropyltrimethoxysilane (MPTMS), are prepared in a solvent, often alcohol-based, with sometimes added water and a catalyst. These agents are crucial for bonding silica to iron oxide surfaces.

Surface Activation

Before silanization, iron oxide particles are cleaned and activated, typically with an acid or a base, to enhance their reactivity and ensure adequate bonding with the silane coupling agents.

Silanization Process

Activated iron oxide particles are mixed with the silane coupling agent solution. Controlled reaction conditions facilitate the bonding of silica groups to the iron oxide surface, creating a covalent bond between them.

Chemical Reactions

The reaction formula varies with the silane agent used. For TEOS, the simplified reaction might be:

Fe2O3+(EtO)4Si→Fe2O3−Si(OEt)3

Here, EtO refers to the ethoxy group.

For MPTMS, the formula might look something like:

Fe2O3+(CH3O)3Si−CH2−CH2−CH2−SH→Fe2O3−Si(OCH3)2−CH2−CH2−CH2−SH

Here, "Si(OCH3)2" denotes the coupling agent bonded to iron oxide, while "SH" is a functional group for further modifications.

Chemist's Notes

The provided chemical formulas represent a simplified reaction scheme. The process may involve complex stages, including hydrolysis and condensation, where ethoxy or methoxy groups from silanes are replaced by hydroxyl groups, forming covalent bonds with iron oxide.

Importance in Semi-Permanent Makeup

While silica coating generally protects iron oxide particles from reactions with proteins like ferritin, the pigment's longevity and appearance in semi-permanent makeup depend on other factors, including pigment formulation, application technique, and individual skin properties. The silanization process offers a protective barrier, enhancing the stability and performance of pigments used in these applications.

9. Conclusions

The occurrence of "red" brows in semi-permanent makeup is a complex issue rooted more in biochemistry than in mere physical or optical phenomena, unlike the "blue" coloration often associated with carbon particles. It's primarily due to the biochemical transformation of iron oxides within the skin over time.

The reddish hue potential is linked explicitly to Fe2O3 (Hematite - Red Iron Oxide - CI 77491) and Fe3O4 (Magnetite - Black Iron Oxide - CI 77499), favored for their larger particle size and photostability. Of these, Black Iron Oxide tends to persist longest in the skin.

Post-implantation during Powder Brows, Hairstrokes, or Microblading procedures, iron oxide pigments typically face one of four destinies: lymphatic removal, macrophage phagocytosis, fibroblast encapsulation, or extracellular matrix entrapment.

The interaction between iron oxide particles and ferritin, a naturally occurring protein, can alter the iron's oxidation state, leading to a reddish, pinkish, or rusty color shift due to altered light diffraction.

The molecular modification of iron oxide particles is crucial to mitigate these interactions and prevent the reddish hue. This can be achieved by silanization, which combines mineral iron oxide with organic polymetal silica, creating a protective barrier. Stabilizing all pigment components, predominantly yellow and red iron oxides, ensures uniform particle size and photostability, contributing to consistent fading.

While termed "hybrid" in the semi-permanent makeup industry, this terminology is not standardized, and descriptions may vary based on the pigment's functional properties. Ultimately, understanding and controlling the biochemistry of iron oxide particles is critical to resolving the issue of "red" brows.